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Although molecular characterization of soil organic carbon is crucial for understanding its dynamics, studies on reclaimed coal mine soil are comparatively limited. Therefore, the primary objective of this study was to ascertain the influence of tree species on the soil organic carbon content and molecular characteristics of soil organic carbon in a chronosequence of reclaimed coal mine soil. To investigate the effects of reclamation time on soil organic carbon characteristics, a chronosequence of three coal mine soil was used, each exhibiting different ages of reclamation: 8, 14, and 25 years. Along a re-vegetation age gradient of 8 to 25 years, the total soil organic carbon content increased. Within the 25 years of restored soil, the FTIR absorption intensities were lowest within the range of 2,920 and 2,850 cm−1, while they were highest within the range of 1,685, 1,425, and 1,285 cm−1which indicates presence of aromatic C=C. This shows that aromatic compounds contributed more significantly to the composition of soil organic carbon compared to aliphatic structures. Based on molecular characteristics, it is suggested that the soil organic carbon in 25-year old revegetated coal mine soil consists of aromatic and recalcitrant carbon. Among three tree species Dalbergia sissoo can be used for reclamation as quality and quantity of carbon found was higher under this tree species. In conclusion, the results indicated that the molecular properties of soil organic carbon were extremely important for understanding the dynamics of soil organic carbon in a restored coal mine soil chronosequence. [ABSTRACT FROM AUTHOR]

Starting in the mid 1970's, researchers, industry leaders, and residents collaborated on one of the world's largest regreening programs in the industrial region of Sudbury, Canada. The Sudbury Regreening Recipe included the application of crushed dolomitic limestone, nitrogen–phosphorus–potassium fertilizers, grass–legume seed mixtures across 8200 ha, and subsequent tree planting across 25 000 ha of acidic metal-contaminated land. The current study evaluated shifts in understory vegetation diversity and soil geochemistry on a chronosequence of sites treated the same way between 1982 and 2012. Fifty-six plant species were identified across the 24 sites, only four of which were planted in the initial remediation effort. Key factors influencing plant community composition and diversity were related to shifts in soil properties over time: bulk density, LFH layer depth, and mineral soil horizon pH. Plant communities differed with stand age and rocky sites had significantly different plant communities and lower canopy cover than less rocky sites. Mineral soil horizon pH increased with age, reflecting the movement of applied dolomite in soil. Despite high concentrations of total copper and nickel in soil, plant succession patterns were generally similar to those in naturally recovering forests demonstrating the overall success of the restoration program. [ABSTRACT FROM AUTHOR]

The objective of this study was to evaluate carbon and (C) and nitrogen (N) of the light organic matter in labile and humic fractions of the soil in a chronosequence of clonal Eucalyptus urophylla. The study was carried out on six different sites in the South-Central region of Maranhão state, northeastern Brazil, inserted in the Cerrado biome. Soil was sampled in five clonal Eucalyptus urophylla S.T. Blake stands of different ages and one in the area with old-growth forest (OG), which represents the native vegetation area. Soil samples were collected in the 0–20, 20–40, and 40–60 cm layers to determine textural class, bulk density, C, and N in the light organic matter of labile and humic fractions. Eucalyptus plantations can have great capacity to increase stocks of soil C and N, humic, and labile fractions over the years, presenting results equal or higher than a native Cerrado forest. Thus, Eucalyptus plantations come as an effective lad use to sink C and increase soil nutrient levels. [ABSTRACT FROM AUTHOR]

Paulownia fortunei, one of the world's fastest growing timber tree species, is universally applied with fertilizer as a management approach to meet the nutrient requirements for efficient cultivation. The substantial effects of fertilizer on soil microorganisms in Paulownia plantations have been empirically tested; however, the successive chronosequence of soil microbial carbon and nitrogen functional genes under different fertilizer application durations remains limited. The objective of this study was to explore the characteristics of soil microorganisms involved in carbon and nitrogen cycling and greenhouse gas (GHG) production under different fertilizer application durations. Different fertilizer treatments, i.e., the short-term group (SG) versus the long-term group (LG), and durations were applied to subtropical plantations in southern China and compared with zonal evergreen broad-leaved forests. Results showed that fertilizer treatment significantly increased the relative abundance of Acidobacteriota and the expression of nirK and nosZ. The functional groups that dominated metabolism in SG and LG treatments belonged to Actinobacteria and Acidobacteriota, respectively, suggesting that the nutrient preference of microorganisms in forest soil may change from copiotrophs to oligotrophs with increasing fertilizer application duration. Correlation network analysis showed that the communities that dominated the carbon and nitrogen cycles belonged to Actinobacteria and Acidobacteriota, respectively, and were closely related to ammonium nitrogen and available iron. Actinobacteria and Acidobacteriota were likely the major taxa that affected soil GHG production under different fertilizer application durations. We concluded that long-term fertilizer use changed the preference of microbial nutrient uptake into recalcitrant nutrients, and the sensitivity of the microbial community to nutrients gradually decreased with increasing fertilizer application time. The dominant Actinobacteria affected soil carbon and nitrogen cycles largely by stimulating denitrification to increase the release of nitrous oxide, which might lead to the loss of nitrogen components and the intensification of the GHG effect with increasing fertilizer application time. [ABSTRACT FROM AUTHOR]

Multiple pathways and outcomes are common in evolutionary sequences for biological and other environmental systems due to nonlinear complexity, historical contingency, and disturbances. From any starting point, multiple evolutionary pathways are possible. From an endpoint or observed state, multiple possibilities exist for the sequence of events that created it. However, for any observed historical sequence—e.g., ecological or soil chronosequences, stratigraphic records, or lineages—only one historical sequence actually occurred. Here, a measure of the embedded complexity of historical sequences based on algebraic graph theory is introduced. Sequences are represented as system states S(t), such that S(t − 1) ≠ S(t) ≠ S(t + 1). Each sequence of N states contains nested subgraph sequences of length 2, 3, ..., N − 1. The embedded complexity index (which can also be interpreted in terms of embedded information) compares the complexity (based on the spectral radius λ1) of the entire sequence to the cumulative complexity of the constituent subsequences. The spectral radius is closely linked to graph entropy, so the index also reflects information in the sequence. The analysis is also applied to ecological state-and-transition models (STM), which represent observed transitions, along with information on their causes or triggers. As historical sequences are lengthened (by the passage of time and additional transitions or by improved resolutions or new observations of historical changes), the overall complexity asymptotically approaches λ1 = 2, while the embedded complexity increases as N2.6. Four case studies are presented, representing coastal benthic community shifts determined from biostratigraphy, ecological succession on glacial forelands, vegetation community changes in longleaf pine woodlands, and habitat changes in a delta. [ABSTRACT FROM AUTHOR]

Purpose: The turnover of organic phosphorus (Po) may be an important way to maintain P supply for plant growth under the phosphorus (P) deficiency in highly weathered tropical soils. However, there is limited information on Po change pattern and how abiotic and biotic factors influence Po transformation in tropical region. Thus, this study was aimed to the characteristics and controls of Po transformation towards the advanced stage of tropical soil evolution. Methods: A well-establish tropical soil chronosequence (0.09, 0.146, 0.64, 1.12, 1.81, and 2.30 million years) derived from basalt in northern Hainan Island, China, was selected and the Po compounds in all soils determined by solution 31P nuclear magnetic resonance spectroscopy. Results: Phosphate monoester showed a rapid increase in the earlier stage of pedogenesis (< 0.15 million year), thereafter declined to the minimum in the 1.12-million-year site and fluctuated in older soils. Meanwhile, the proportion of labile Po (including phosphate diester and its degradation products) increased continuously across the chronosequence, suggesting that long-term tropical soil evolution promoted labile Po accumulation that was vital to maintain P supply in highly weathered and P-deficient soil. Redundancy analysis revealed that Po transformation was jointly affected by soil total nitrogen, total organic carbon, phytase, and amorphous iron, accounting for 37.5% (p < 0.01), 29.5% (p < 0.01), 20.7% (p < 0.05), and 14.8% (p < 0.05) of explanation in the variations of Po compounds, respectively. Conclusion: Our study has supplemented the blank of Po transformation during tropical soil evolution over a 2.30-million-year time scale and emphasizes the important role of soil C, N in regulating Po changes. [ABSTRACT FROM AUTHOR]

The Golan Heights plateau in northern Israel is underlaid by volcanic rocks ranging in age from ~5.5 to 0.1 Ma. Throughout the Golan Heights, these rocks are covered by shallow soils that rarely exceed 0.5 m in depth. The soils are generally assumed to form a chronosequence, in which their ages correspond to those of the basalts they cover. Such age correspondence would imply that the soils have been slowly accumulating over hundreds of thousands to a few million years, suggesting a generally stable system. The ages of these soils and their temporal correlation to the basalts, however, have never been determined or tested. Here, we present age constraints for the soils of the Golan Heights. Soils were surveyed and sampled with their corresponding basalt bedrock. Mass balance calculations based on conservative immobile elements, coupled with 36Cl-based basalt denudation rates, suggest that the soil ages are decoupled from the ages of the underlying basalts, and represent up to a few thousand years of soil production, at most. This time frame is orders of magnitude shorter than the basalt age, challenging the prevalent assumption that the soils form a chronosequence. Our findings strongly suggest that erosion is a significant factor controlling soil formation and accumulation on the plateau, despite the generally flat morphology of the Golan Heights. The erosion is associated with tectonic activity along the Dead Sea transform, with the development of the Kinarot and Hula valleys, and with the consequential development of drainage systems of various sizes on the plateau. Throughout the Golan Heights, the timing of volcanic activity in relation to the development of the valleys and drainage systems also appears to strongly affect soil development and accumulation. [ABSTRACT FROM AUTHOR]

Aim: Theory suggests that the diversity of molecules in soil organic matter (SOM functional diversity) provides key insights on multiple ecosystem services. We aimed to investigate how and why SOM functional diversity and composition change as topsoils develop, and its implications for key soil functions (e.g., from nutrient pool to water regulation). Location: We reported data on 16 soil chronosequences globally distributed in nine countries from six continents. Time Period: 2016–2017. Major Taxa Studied: Soil microbes (bacteria and fungi) and vascular plants. Methods: SOM functional diversity and composition without mineral interference were measured using diffuse reflectance mid‐infrared Fourier transform spectroscopy (DRIFT). We aimed to characterize the main environmental factors related to SOM functional diversity and composition. Also, we calculated the links among SOM functional diversity and key soil functions. Results: We found that SOM functional diversity declines after millions of years of soil formation (pedogenesis). We further showed that increases in plant cover and productivity led to a higher ratio of reduced (e.g., alkanes) over oxidized carbon forms (i.e., C: O‐functional groups ratio), which was positively correlated to SOM functional diversity as soils age. Our findings indicated that the plant footprint (i.e., the accumulation of plant‐derived material promoting the C: O‐functional group ratio) would explain the reduction of SOM functional diversity as ecosystems develop. Moreover, the dissimilarity in SOM composition consistently increased with soil age, with the soil development stage emerging as the main predictor of SOM dissimilarity across contrasting biomes. Main Conclusions: Our global survey contextualized the natural history of SOM functional diversity and composition during long‐term soil development. Together, we showed how plant footprint drives the losses of SOM functional diversity with increasing age, which might provide a novel mechanism to explain typically reported losses in ecosystem functions during ecosystem retrogression. [ABSTRACT FROM AUTHOR]

In high-altitude environments, most of the debris-free glacier forelands are increasingly widening and the bare surfaces left by retreating glaciers offer the opportunity to investigate the evolution of soil through time. The main aim of this study is to discuss the applicability of a chronosequence approach in a deglaciated area, by considering the role of different soil forming factors. A study case has been selected (Alpe Veglia, Lepontine Alps), where field and laboratory characterizations were performed along a transect of 12 soil profiles from the proglacial area of the Aurona Glacier to the Alpe Veglia hollow, crossing different age glacial deposits. The results of soil physical and chemical analyses underline a time-trend of soil properties. On the other hand, even if the soil properties variability along the transect can be mainly explained according to the soil chronosequence approach, the data seem to highlight how the various soil forming factors (e.g. parent material, relief, vegetation) influence soil features, partly masking the effect of the time factor inducing a divergence from a traditional chronosequence. In particular, the morphology of the surrounding reliefs, depending on bedrock lithologies and structures, and the geomorphic dynamics seem to affect soil formation and evolution. [ABSTRACT FROM AUTHOR]

Glaciers retreating due to global warming create important new habitats, particularly suitable for studying ecosystem development where nitrogen is a limiting factor. Nitrogen availability mainly results from microbial decomposition and transformation processes, including nitrification. AOA and AOB perform the first and rate-limiting step of nitrification. Investigating the abundance and diversity of AOA and AOB is essential for understanding early ecosystem development. The dynamics of AOA and AOB community structure along a soil chronosequence in Tianshan No. 1 Glacier foreland were analyzed using qPCR and clone library methods. The results consistently showed low quantities of both AOA and AOB throughout the chronosequence. Initially, the copy numbers of AOB were higher than those of AOA, but they decreased in later stages. The AOB community was dominated by "Nitrosospira cluster ME", while the AOA community was dominated by "the soil and sediment 1". Both communities were potentially connected to supra- and subglacial microbial communities during early stages. Correlation analysis revealed a significant positive correlation between the ratios of AOA and AOB with soil ammonium and total nitrogen levels. These results suggest that variations in abundance and diversity of AOA and AOB along the chronosequences were influenced by ammonium availability during glacier retreat. [ABSTRACT FROM AUTHOR]

The chronosequence of soils buried under constructions of different ages at the large (3.5 m in height and 74 m in diameter) Shumny Kurgan in the Krasnodar region has been studied. The kurgan was built sequentially by the people of Catacomb (28th–22nd centuries BC) and Srubnaya (15th–10th centuries BC) cultures and includes five constructions made of the material of local soils and anthropogenic admixtures. Each of the subsequent constructions overlapped the previous one and went beyond it, covering some additional space. This allows us to study a consecutive series of soils buried under the constructions. During the kurgan building (28th–10th centuries BC), the morphological and physicochemical properties of the soils changed: the content of organic matter and magnetic susceptibility increased, whereas the mixing up of the upper horizons by burrowing animals, the content of carbonates, and the exchangeable sodium percentage decreased. The direction of these changes in the properties of the materials of kurgan constructions over time agree with changes in the properties of corresponding buried soils. For the uneven-aged constructions of the kurgan, local soils were used, which had different properties at the stages of the construction. These soils occupied a significantly larger area than the kurgan, which increases the reliability of the study. Evolutionary changes in the properties of buried soils and earth materials of kurgan structures are indicative of the climatic trend during the long-term kurgan construction—an increase in atmospheric moistening and a decrease in the mean annual temperature from the Early Catacomb to Srubnaya cultures. An independent palynological analysis of buried paleosols confirms this conclusion about the tendency of climate changes. According to micromorphological data, the Early Catacomb time can be additionally characterized as an arid epoch, which manifested itself in soil cracking and accumulation of carbonates in the upper part of soil profiles. Based on the structure and properties of the kurgan, it is possible to identify technologies of the construction, which included tamping down of earthy material in dry and wet states; its mixing; and adding of river silt, charcoal, and bones. [ABSTRACT FROM AUTHOR]

Rubber tree plantations (Hevea brasiliensis) are expanding into the tropical regions of southwest China to ensure production to meet the growing demand for latex. The effects of long-term plantations on soil carbon processes are still unclear. Also, the effects of the plant's rhizosphere on the decomposition of soil organic matter (SOM) play a crucial role in predicting soil carbon dynamics. The rhizosphere and soils corresponding to a chronosequence of ages (4, 15 and 30 years) of rubber plantations were collected and incubated to determine the effect of the rhizosphere (RE) on SOM decomposition. We also examined the soil physicochemical properties; bacterial community structure; and root morphological, chemical, and physiological traits to further explore the underlying mechanisms of the RE on SOM decomposition. The REs on SOM decomposition varied significantly in the different age classes of the rubber plantations, and the higher the REs on SOM decomposition in an older plantation might limit the accumulation of organic carbon in the soil. Root traits, including the specific root length, root nitrogen content, and root carbon/nitrogen ratio, varied significantly in response to the plantation age and explained more of the variance in the RE on SOM decomposition than the soil and microbial properties. Due to the changing root morphological and chemical traits along the age chronosequence, the rhizosphere bacterial community composition tended to shift the carbon utilisation strategy and the bulk soil nitrogen content decreased. These variations also affected the RE on SOM decomposition. Our results indicate that the development of rubber plantations would prevent soil carbon accumulation, especially in the rhizosphere, by increasing the RE on SOM decomposition, which would be predicated by root morphological and chemical traits. [ABSTRACT FROM AUTHOR]

Anthropogenic changes to soil properties and development can dominate soil systems, particularly in coal mining-impacted landscapes of the Appalachian region of the United States. Historical mining operations deposited spoils which are developing into mine soils in chronosequences, allowing for a correlation between emplacement age and rates of change in soil properties. The study site was in the Huff Run Watershed (Mineral City, OH, USA) with a series of eleven spoil piles that were deposited over a 30-year time period. Surface soils were analyzed for bulk density, loss on ignition (LOI) as a proxy for organic matter, particle size, and bulk mineralogical (by X-ray diffraction) and elemental (by X-ray fluorescence) compositions. The following linear trends were observed across the transect from older to younger mine soils: bulk density increased from 1.0 cm−3 to 1.5 g cm−3; LOI decreased from ~20% to 5%; the content of sand-sized particles and quartz decreased from ~50% to 30% and 50% to 25%, respectively, with a corresponding increase in the contribution of clay mineral from ~25% to 60%; and Fe and other trace metals (Cu, Ni, Pb, Sb, Sn, and Te) decreased in concentration, while Al, Mg, and K increased in concentration. These trends are likely the result of: (1) organic matter accumulation as vegetation becomes more abundant over time; (2) transport of clays out of more recently emplaced waste; and (3) oxidative dissolution of primary sulfides releasing Fe and other trace metals followed by re-precipitation of secondary Fe-phases and trace metal sequestration. The findings presented here provide insight into the future behavior of these materials and can potentially be used to assess the inferred age of previously unexamined mine soils across a wider geographic area. These results can also inform decisions related to reclamation activities and ecosystem restoration. [ABSTRACT FROM AUTHOR]

Primary minerals that enter soils through bedrock weathering and atmospheric deposition can generate poorly crystalline minerals (PCM) that preferentially associate with soil organic carbon (SOC). These associations hinder microbial decomposition and the release of CO2 from soils to the atmosphere, making them a critical geochemical control on terrestrial carbon abundance and persistence. Studies that explore these relationships are typically derived from soil chronosequences that experience negligible erosion and thus do not readily translate to eroding landscapes. Here, we propose a theoretical framework to estimate steady-state PCM density and stocks for hilly and mountainous settings by coupling geochemical and geomorphic mass balance equations that account for soil production from bedrock and dust, soil erosion, PCM formation from weathering, and the transformation of PCMs into crystalline phases. We calculate an optimal erosion rate for maximum PCM abundance that arises because PCMs are limited by insufficient weathering at faster erosion rates and loss via "ripening" into more crystalline forms at slower erosion rates. The optimal erosion rate for modeled hilltop soil is modulated by reaction rate constants that govern the efficiency of primary mineral weathering and PCM ripening. By comparing our analysis with global compilations of erosion and soil production rates derived from cosmogenic nuclides, we show that landscapes with slow-to-moderate erosion rates may be optimal for harboring abundant PCM stocks that can facilitate SOC sequestration and limit turnover. Given the growing array of erosion-topography metrics and the widespread availability of high-resolution topographic data, our framework demonstrates how weathering and critical zone processes can be coupled to inform landscape prioritization for persistent SOC storage potential across a broad range of spatial and temporal scales. [ABSTRACT FROM AUTHOR]

The adsorption characteristics, availability, and a loss risk of phosphorus (P) in paddy soil chronosequences had not been well established. In the present study, P adsorption characteristics of paddy soil chronosequence with 0, 7, 22, or 80 years of paddy cultivation history (PS0, PS7, PS22, and PS80, respectively) were identified by P adsorption isotherm, envelope, and stirred‐flow chamber (SFC) kinetics, along with the assessment of P availability and loss risks. Results indicated that P adsorption and desorption followed the same order of PS0 > PS7 > PS22 > PS80. Pearson's correlation analysis revealed P adsorption capacity was significantly and positively correlated with the concentrations of both free iron (Fe) and aluminum (Al) (hydro)oxides (Fed and Ald, respectively), suggesting that the major P sorbents were Fed and Ald. Findings from SFC adsorption kinetics suggested that the kinetics of both P adsorption and desorption were biphasic, being fast in the first 100 min (75.11%–87.57% of P adsorbed and 79.00%–88.65% of P released), followed by a slow phase for the remaining 180 min. Bray‐P increased with the duration of rice cultivation and reached a maximum of 77.90 mg kg−1 at PS80, along with the highest P saturation degree and equilibrium phosphorus concentrations of 7.56% and 2.33 mg L−1, respectively. Hence, with an increasing duration of paddy cultivation, there was a less pronounced P sink function and a lower P availability, but a higher P loss risk, indicating that P availability in the younger and loss risk in the older Ultisol‐derived paddy soils deserve greater attention. Core Ideas: P adsorption, desorption kinetics by SFC were linked closer to practical P behavior.P retention on Ultisol‐derived paddy soils is due mainly to complexation and precipitation.Higher available P, greater P loss risk occurred as paddy cultivation duration increased. [ABSTRACT FROM AUTHOR]

Soil chronosequences derived from landslides with certain time series are the great avenue to elevate our understanding on the processes of pedogenesis, nutrient dynamics, and ecosystem evolution. However, the construction of reliable soil chronosequence from historical landslides remains intricate. Here, we presented a 22,000-year soil chronosequence from multiple landslides on the upper reach of Minjiang River, western China. The variation in a variety of pedogenesis indices and soil nutrients verified the reliability of the chronosequence. The silica-alumina ratio and silica sesquioxide ratio decreased significantly with soil age. This reflected the enrichment of Al/Fe/Ti oxides but the depletion of Si oxides with the soil development. Meanwhile, the values of the Chemical Index of Weathering and the Chemical Index of Alteration increased significantly with soil age, especially from 5 to 89 years. These variations were attributed to the soil weathering, which led to the destruction of soil minerals with the rapid loss of most of cations (e.g., K, Na, Ca, and Mg) during the soil development. The concentrations of carbon and nitrogen in topsoil increased with soil age, and the carbon accumulation rate slowed significantly from 5,500 to 22,000 years. The total phosphorus concentrations decreased with soil age, suggesting the gradual loss of soil phosphorus with soil development. The results indicate that the landslide chronosequence established on the upper reach of Minjiang River is reliable and delineates a long-term soil development process, which will provide a great platform for further improvement of biogeochemical theories and understanding sustainable vegetation restoration. [ABSTRACT FROM AUTHOR]

Purpose: To test the interconnections between pedogenetic drivers featured by climate, parent material, weathering intensity, soil properties, and their influence on inorganic and organic P compounds (31P NMR) in temperate ecosystems, and validation of the theoretical concept of P pools. Methods: Data from the literature on the chronosequences of temperate soils under native vegetation were used to build a structural model. Results: The structural model was satisfactorily fitted and pointed out that the soil property pool, which is featured by measurable variables such as total P, clay, and organic carbon, had a direct and positive relationship with the inorganic P (β = 0.85) (Pi—composed of pyrophosphate, orthophosphate, and polyphosphate variables) and organic P (β = 0.95) (Po—composed of variables DNA, IHPs, and phosphonates) pools, regulating soil P availability. The climate pool, featured by measurable temperature and precipitation variables, had indirect and negative relationships (via soil properties pool) with Pi and Po compounds; this suggests a reduction in soil P availability over time in temperate humid environments. The weathering and parent material pools had positive indirect relationships (via soil properties pool) with the Po and Pi pools. The model explained 97% and 91% variances (R2) in the Pi and Po pools, respectively. Conclusions: Our study shows that the Pi and Po compounds are closely dependent on soil development processes featured by climate, parent material, weathering, and soil properties in temperate ecosystems. There was low direct dependence of the Pi pool on the Po pool. [ABSTRACT FROM AUTHOR]

Mining activities modify both aboveground and belowground ecological communities, presenting substantial challenges for restoration. The soil microbiome is one of these impacted communities and performs important ecosystem functions but receives limited focus in restoration. Sequencing soil DNA enables accurate and cost‐effective assessment of soil microbiota, allowing for comparisons across land use, environmental, and temporal gradients. We used amplicon sequencing of the bacterial 16s rRNA gene extracted from soil samples across a 28‐year post‐mining rehabilitation chronosequence to assess soil bacterial composition and diversity following rehabilitation at a bauxite mine in Western Australia's jarrah forest. We show that while bacterial alpha diversity did not differ between reference and rehabilitated sites, bacterial community composition changed dramatically across the chronosequence, suggesting strong impacts by mining and rehabilitation activities. Bacterial communities generally became increasingly similar to unmined reference sites with time since rehabilitation. Soil from sites rehabilitated as recently as 14 years ago did not have significantly different communities to reference sites. Overall, our study provides evidence indicating the recovery of soil bacterial communities toward reference states following rehabilitation. Including several ecological reference sites revealed substantial natural variability in bacterial communities from within a single mine site. We urge future restoration chronosequence studies to sample reference sites that geographically span the restored sites and/or are spatially paired with restored sites to ensure this variability is captured and to improve any inferences on recovery. [ABSTRACT FROM AUTHOR]

Pedogenetic features of the soils could be a proxy for revealing the landform surface processes. Our work first analyzed the particle size distributions and lithological discontinuities (LDs) of the soils in the midstream of the Zoushui River, central Taiwan. The results showed that the parental materials of the soils derive from mixed sediments of the Zoushui River and its tributaries, and the LDs of some soils suggested multi-depositional events with homogeneous lithology. Then, we proposed a soil chronosequence of Inceptisols, Ultisols, and Oxisols, over the Pleistocene timescale. There was a very well-defined semilogarithmic relationship between weighted profile development index (WPDI) values and soil age with correlation coefficients (r) greater than 0.9. The age of the soils did not certainly agree with the interglacials of the main marine isotope stage (MIS). However, the soils started to develop only after being aggraded by relatively warm and humid periods or by extreme rain events in cool and dry periods. Irrespective of whether the soils had started to develop, tectonic downcutting, providing clear altitudinal separation of the terrace treads, could inevitably happen later (or almost synchronologically) to ensure stabilities of the tread surfaces. [ABSTRACT FROM AUTHOR]

Simple Summary: We characterized the fungal organisms present in soils at James Ross Island, north-east Antarctic Peninsula, using DNA metabarcoding. Taxa detected included members of the widespread phyla Ascomycota, Basidiomycota and Mortierellomycota. Additionally, the uncommon phyla Chytridiomycota, Rozellomycota, Monoblepharomycota, Zoopagomycota and Basidiobolomycota were detected. Unknown fungi and taxa identified at generic and specific levels dominated the assemblages. The fungal sequence assemblages displayed high diversity and richness, and moderate dominance, and included taxa known to play saprophytic, pathogenic and symbiotic functions. Soils of Clearwater Mesa contain a complex fungal community, including fungal groups considered rare in Antarctica, dominated by cold-adapted cosmopolitan, endemic, saprotrophic and phytopathogenic taxa. We studied the fungal diversity present in soils sampled along a deglaciated chronosequence from para- to periglacial conditions on James Ross Island, north-east Antarctic Peninsula, using DNA metabarcoding. A total of 88 amplicon sequence variants (ASVs) were detected, dominated by the phyla Ascomycota, Basidiomycota and Mortierellomycota. The uncommon phyla Chytridiomycota, Rozellomycota, Monoblepharomycota, Zoopagomycota and Basidiobolomycota were detected. Unknown fungi identified at higher hierarchical taxonomic levels (Fungal sp. 1, Fungal sp. 2, Spizellomycetales sp. and Rozellomycotina sp.) and taxa identified at generic and specific levels (Mortierella sp., Pseudogymnoascus sp., Mortierella alpina, M. turficola, Neoascochyta paspali, Penicillium sp. and Betamyces sp.) dominated the assemblages. In general, the assemblages displayed high diversity and richness, and moderate dominance. Only 12 of the fungal ASVs were detected in all chronosequence soils sampled. Sequences representing saprophytic, pathogenic and symbiotic fungi were detected. Based on the sequence diversity obtained, Clearwater Mesa soils contain a complex fungal community, including the presence of fungal groups generally considered rare in Antarctica, with dominant taxa recognized as cold-adapted cosmopolitan, endemic, saprotrophic and phytopathogenic fungi. Clearwater Mesa ecosystems are impacted by the effects of regional climatic changes, and may provide a natural observatory to understand climate change effects over time. [ABSTRACT FROM AUTHOR]

An accurate assessment of the effect of long-term rice cultivation on K-supplying capacity and adsorption characteristics of paddy soils has theoretical and practical significance for rational application of K fertilizers. We measured changes in basic soil properties and K adsorption isotherms in a representative subtropical paddy soil chronosequence in Southern China. Results showed that mean water dissolvable K and non-exchangeable K contents of paddy soils (27.0 and 184.8 mg kg−1) were higher than those of original soils (15.5 and 169.5 mg kg−1), but the mean exchangeable K contents showed the opposite trend (paddy soils, 37.1 mg kg−1; original soils, 52.5 mg kg−1). Long-term paddy cultivation caused reduced K-supplying capacity and K+ adsorption capacity of paddy soils in the red soil regions, which was attributed to the rapid loss of sorbents (e.g. Fed and clay) by leaching and the competitive occupation of sorption sites by the accumulated soil organic matter. The promotion of sustainable and balanced K fertilizer inputs and appropriate increase in short-term applications of K fertilizer (K fertilizer input > K output from harvest) during application of N and P fertilizers to paddy soils were necessary to maintain the K-supplying capacity of soils and the crop yield. [ABSTRACT FROM AUTHOR]

Belowground organisms play critical roles in maintaining multiple ecosystem processes, including plant productivity, decomposition, and nutrient cycling. Despite their importance, however, we have a limited understanding of how and why belowground biodiversity (bacteria, fungi, protists, and invertebrates) may change as soils develop over centuries to millennia (pedogenesis). Moreover, it is unclear whether belowground biodiversity changes during pedogenesis are similar to the patterns observed for aboveground plant diversity. Here we evaluated the roles of resource availability, nutrient stoichiometry, and soil abiotic factors in driving belowground biodiversity across 16 soil chronosequences (from centuries to millennia) spanning a wide range of globally distributed ecosystem types. Changes in belowground biodiversity during pedogenesis followed two main patterns. In lower-productivity ecosystems (i.e., drier and colder), increases in belowground biodiversity tracked increases in plant cover. In more productive ecosystems (i.e., wetter and warmer), increased acidification during pedogenesis was associated with declines in belowground biodiversity. Changes in the diversity of bacteria, fungi, protists, and invertebrates with pedogenesis were strongly and positively correlated worldwide, highlighting that belowground biodiversity shares similar ecological drivers as soils and ecosystems develop. In general, temporal changes in aboveground plant diversity and belowground biodiversity were not correlated, challenging the common perception that belowground biodiversity should follow similar patterns to those of plant diversity during ecosystem development. Taken together, our findings provide evidence that ecological patterns in belowground biodiversity are predictable across major globally distributed ecosystem types and suggest that shifts in plant cover and soil acidification during ecosystem development are associated with changes in belowground biodiversity over centuries to millennia.

Belowground organisms play critical roles in maintaining multiple ecosystem processes, including plant productivity, decomposition, and nutrient cycling. Despite their importance, however, we have a limited understanding of how and why belowground biodiversity (bacteria, fungi, protists, and invertebrates) may change as soils develop over centuries to millennia (pedogenesis). Moreover, it is unclear whether belowground biodiversity changes during pedogenesis are similar to the patterns observed for aboveground plant diversity. Here we evaluated the roles of resource availability, nutrient stoichiometry, and soil abiotic factors in driving belowground biodiversity across 16 soil chronosequences (from centuries to millennia) spanning a wide range of globally distributed ecosystem types. Changes in belowground biodiversity during pedogenesis followed two main patterns. In lower-productivity ecosystems (i.e., drier and colder), increases in belowground biodiversity tracked increases in plant cover. In more productive ecosystems (i.e., wetter and warmer), increased acidification during pedogenesis was associated with declines in belowground biodiversity. Changes in the diversity of bacteria, fungi, protists, and invertebrates with pedogenesis were strongly and positively correlated worldwide, highlighting that belowground biodiversity shares similar ecological drivers as soils and ecosystems develop. In general, temporal changes in aboveground plant diversity and belowground biodiversity were not correlated, challenging the common perception that belowground biodiversity should follow similar patterns to those of plant diversity during ecosystem development. Taken together, our findings provide evidence that ecological patterns in belowground biodiversity are predictable across major globally distributed ecosystem types and suggest that shifts in plant cover and soil acidification during ecosystem development are associated with changes in belowground biodiversity over centuries to millennia.

Soil hydrologic processes play an important role in the hydro-pedo-geomorphological feedback cycle of landscape evolution. Soil properties and subsurface flow paths both change over time, but due to a lack of observations, subsurface water flow paths are often not properly represented in soil and landscape evolution models. We investigated the evolution of subsurface flow paths across a soil chronosequence in the calcareous glacier forefield at the Griessfirn glacier in the Swiss Alps. Young soils developed from calcareous parent material usually have a high pH value, which likely affects vegetation development and pedogenesis and thus the evolution of subsurface flow paths. We chose four glacial moraines of different ages (110, 160, 4 900, and 13 500 years) and conducted sprinkling experiments with the dye tracer Brilliant Blue on three plots at each moraine. Each plot was divided into three equal subplots, and dyed water was applied with three different irrigation intensities (20, 40, and 60 mm h -1) and an irrigation amount of 40 mm. Subsequent excavation of soil profiles enabled the tracing of subsurface flow paths. A change in flow types with increasing moraine age was observed from a rather homogeneous matrix flow at 110 and 160 years to heterogeneous matrix and finger-shaped flow at 4 900 and 13 500 years. However, the proportion of preferential flow paths is not necessarily directly related to the moraine age but rather to soil properties such as texture, soil layering, organic matter content, and vegetation characteristics such as root length density and biomass. Irrigation intensity had an effect on the number of finger-shaped flow paths at the two old moraines. We also found that flow paths in this calcareous material evolved differently compared to a previous study in siliceous material, which emphasizes the importance of parent material for flow path evolution. Our study provides a rare systematic dataset and observations on the evolution of vertical subsurface flow paths in calcareous soils, which is useful to improve their representation in the context of landscape evolution modeling. [ABSTRACT FROM AUTHOR]

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Microbial diversity plays an important role in the decomposition of soil organic matter. However, the pattern and drivers of the relationship between microbial diversity and decomposition remain unclear. In this study, we followed the decomposition of organic matter in soils where microbial diversity was experimentally manipulated. To produce a gradient of microbial diversity, we used soil samples at two sites of the same chronosequence after brown coal mining in Sokolov, Czech Republic. Soils were X-ray sterilized and inoculated by two densities of inoculum from both soils and planted with seeds of six local plant species. This created two soils each with four levels of microbial diversity characterized by next-generation sequencing. These eight soils were supplied, or not, by litter of the bushgrass Calamagrostisepigejos, and microbial respiration was measured to assess the rate of decomposition. A strong positive correlation was found between microbial diversity and decomposition of organic matter per gram of carbon in soil, which suggests that microbial diversity supports decomposition if the microbial community is limited by available carbon. In contrast, microbial respiration per gram of soil negatively correlated with bacterial diversity and positively with fungal biomass, suggesting that in the absence of a carbon limitation, decomposition rate is controlled by the amount of fungal biomass. Soils with the addition of grass litter showed a priming effect in the initial stage of decomposition compared to the samples without the addition of litter. Thus, the relationship between microbial diversity and the rate of decomposition may be complex and context dependent. [ABSTRACT FROM AUTHOR]

Coastal wetlands are significant sources of nitrous oxide (N 2 O), a potent greenhouse gas and ozone depleting agent. Land reclamation is known to change N 2 O emissions from coastal wetlands, but the long-term impacts on N 2 O sources and emissions are not well-understood. Here, we performed respiration inhibition and molecular techniques to dissect the long-term effects of coastal reclamation on bacterial, fungal and overall N 2 O emissions across a 53-year chronosequence of paddy soils reclaimed from coastal wetlands. Our findings showed that reclamation of coastal wetlands to paddy soils generally promoted N 2 O emissions in the chronosequences, despite a significant reduction in uncultivated paddy soils. The observed increase in N 2 O emissions was primarily attributed to an imbalance between N 2 O production and consumption driven by bacterial denitrifiers. Additionally, reclamation of coastal wetlands to paddy soils shifted N 2 O emissions from fungal to bacterial predominance in the chronosequences, with denitrification mediated by bacterial denitrifiers dominating bacterial N 2 O emissions. By integrating the analysis of N 2 O emission rates with soil physicochemical and microbiological properties, we demonstrated that the reduced salinity following coastal reclamation diminished the relative abundance of key fungal denitrifiers (e.g., Paraconiothyrium, Penicillium and Trichoderma), thus lowering the fungal contribution to N 2 O emissions. This study provides novel insights into the long-term influences of coastal reclamation on the sources and emissions of N 2 O, and enhance our knowledge of the underlying mechanisms driving these impacts, thereby contributing to improving future models of N 2 O emissions from coastal ecosystems under global change. [Display omitted] • Long-term impacts of coastal reclamation on N 2 O source and emission were explored. • Influences of coastal reclamation on N 2 O emission depend on reclamation types. • Coastal reclamation shifted N 2 O emission from fungal to bacterial dominance. • Bacterial denitrifiers mediated denitrification dominated bacterial N 2 O emission. • Reduction in the abundance of key fungal denitrifiers led to shift in N 2 O source. [ABSTRACT FROM AUTHOR]

Iron (Fe) is an important element for the terrestrial and marine ecosystems through its biogeochemical cycling on the Earth's surface. China has a long rice cultivation history, with extensive rice distribution across many types of paddy soils. Paddy soils are the largest anthropogenic wetlands on earth with critical roles in ecosystem functions. The periodic artificial submergence and drainage during paddy soil evolution result in significant changes in soil moisture regime and redox conditions from the natural soils, which facilitate the increase of Fe solubility and mobilization. However, there is a lack of systematic assessment on the magnitude of the migration and loss amount of Fe from paddy soils. In order to quantify the Fe loss and assess the dynamic evolution of Fe in the soils after rice cultivation, seven paddy soil chronosequences derived from different landscapes (bog, plain, terrace) and parent materials (acidic, neutral, calcareous) with cultivation history from 0 to 2,000 yr were studied. Results showed that the rates and trajectories of Fe evolution showed distinct patterns among the studied seven paddy soil chronosequences. However, net losses of Fe from 1 m soil depth occurred at all studied paddy soil chronosequences regardless of the original landscapes and parent materials. Fe in the paddy soils derived from the calcareous lacustrine sediments in the bog area showed a slight accumulation during the initial stage (50 yr) of paddy cultivation, with a loss rate of 0.026 kg m−2 yr−1 during the 50- to 500-yr time period. For the paddy soils developed on the calcareous marine sediments in the plain area, Fe evolution was dominated by the internal movement in soil profiles through coupled reducing-eluviation reactions in the surface horizons and oxidation-illuviation in the subsurface horizons within 1,000 yr of paddy cultivation, with an averaged net loss rate of 0.029 kg m−2 yr−1 during the 1,000- to 2,000-yr time period of rice cultivation. In contrast, Fe in the paddy soils derived from the acidic and neutral parent materials in the plain and terraced upland areas was rapidly lost during the initial stage of paddy cultivation, with a maximum loss rate of 1.106 kg m−2 yr−1, while the Fe loss rate decreased gradually with increasing paddy cultivation age. Soil pH, CaCO3, and organic matter contents of the original soils, the length of time of paddy cultivation, landscape types and positions, and changes in soil moisture regime and redox condition induced by artificial submergence and drainage were the main factors controlling the rates and trajectories of Fe loss during paddy soils evolution. The amount of Fe loss caused by rice cultivation at the national scale was estimated based on the data collected from this study and the literature. The Fe loss fluxes of paddy soils in China were about 46.4–195.7 Tg yr−1, and the amounts of Fe losses from paddy fields nationwide were about 5,121.5–9,412.2 Tg. Quantifying Fe loss from paddy fields is important to scientifically assess the impact of paddy cultivation on the Fe biogeochemical cycle. [ABSTRACT FROM AUTHOR]

Reclaimed Mine Soil (RMS) is the type of high compacted and nutrient exhausted soil, due to the mining and reclamation operations. The soil aggregate associated carbon (C), nitrogen (N), and isotope can be a platform to understand the pedogenic process of reclaimed mine soil. This study aims to monitor the soil aggregate recovery and Soil Organic Matter (SOM) formation. Different sorts of age chronosequence soil (0, 3, 12, 14, 17, 25, 28, and 32 a) were collected from the Robinia pseudoacacia L. forests in the Pingshuo opencast coal mine in China. Moreover, the soil was selected from adjacent and undisturbed Populus simonii forest as a reference (CK) as well. The wet-sieving method was used to separate the fractions of soil aggregate, and the aggregate-associated C, N, 13C, and 15N isotopes. The results showed that: 1) The proportion of >250-2 000 μm aggregate in the 32 a soil was 737.02% higher than that in the 0a soil, whereas, the proportion of 53-250 μm in the 32 a soil was 19.25% lower than that in the 0a soil, indicating that the reclamation operations destroyed the structure and stability of water-stable aggregate. Moreover, the mean weight diameter of soil aggregate in the 32 a soil was 133% higher than that the in 0a soil, indicating the excellent recovery of the structure and stability with the ages. 2) Soil aggregate associated C and N increased with the reclamation time. The >2 000 μm and >250-2 000 μm associated C and N were dominated in the total C and N. In addition, the aggregate-associated C, N, and C/N ratio increased with the time. Specifically, the large-size aggregate (>250 μm) associated C/N was significantly higher than that of the microaggregate (P<0.05). 3) The δ13C values were differed from -15.14‰--26.40‰, while the δ15N values were ranged from 1.13‰-10.87‰. More importantly, the δ13C values decreased with the time in the soil aggregate >2 000 μm, >250-2 000 μm, and lower than 53 μm, the δ15N values decreased in the >2 000 μm as well. The 13C isotopes were significantly enriched in the soil aggregate 53-250 μm and lower than 53 μm fractions, compared with the large-size aggregates (P<0.05). It infers that the soil C was incorporated into the RMS from the large-size to small-size aggregate fractions during the pedogenic process. 4) The proportion of the new C was accounted for over 80% of the total C in the soil aggregate >2 000 and >250-2 000 μm, without the significant temporal variation (P>0.05). However, the proportion of the new C increased significantly in the lower than 53 μm fraction over 17 years after reclamation, whereas the proportion remained stable after that, indicating the nearly saturated recalcitrance pool (<53 μm C) after 17-year reclamation. Overall, the reclamation operations significantly increased the proportions of small-size soil aggregates. However, the vegetation restoration can be expected to facilitate the recovery of aggregate structure, stability and aggregate associated C and N. [ABSTRACT FROM AUTHOR]

Summary: Photoautotrophic soil cyanobacteria play essential ecological roles and are known to exhibit large changes in their diversity and abundance throughout early succession. However, much less is known about how and why soil cyanobacterial communities change as soil develops over centuries and millennia, and the effects that vegetation have on such communities.We combined an extensive field survey, including 16 global soil chronosequences across contrasting ecosystems (from deserts to tropical forests), with molecular analyses to investigate how the diversity and abundance of photosynthetic and nonphotosynthetic soil cyanobacteria are affected by vegetation change during soil development, over time periods from hundreds to thousands of years.We show that, in most chronosequences, the abundance, species richness and community composition of soil cyanobacteria are relatively stable as soil develops (from centuries to millennia). Regardless of soil age, forest chronosequences were consistently dominated by nonphotosynthetic cyanobacteria (Vampirovibrionia), while grasslands and shrublands were dominated by photosynthetic cyanobacteria. Chronosequences undergoing drastic vegetation shifts (e.g. transitions from grasslands to forests) experienced significant changes in the composition of soil cyanobacterial communities.Our results advance our understanding of the ecology of cyanobacterial classes, and of the understudied nonphotosynthetic cyanobacteria in particular, and highlight the key role of vegetation as a major driver of their temporal dynamics as soil develops. [ABSTRACT FROM AUTHOR]

Space-for-time substitution, also known as pseudo chronosequence (PCS), is often used as a method to assess temporal changes in ecosystems without having to wait for the time span that the study is supposed to cover. However, the suitability of PCS studies is often questioned because convergent development of spatially separated plots over time is rarely guaranteed even under optimal conditions. To assess whether the PCS approach is justified and suitable, we studied the nematode soil food web development of free-living nematodes and biological and chemical soil components related to C and N mobilization (CO 2 and NO 3 -) and immobilization (microbial and soil organic carbon), in a PCS focusing on the critical early reclamation period of four years after open-cast lignite mining, and compared it with a real chronosequence (RCS) of a reclamation site monitored over four years. We hypothesized that: (I) nematode-derived indices indicate the same course of nematode soil food web development in the PCS and RCS, tolerating a range of variability in weather conditions, soil components, and management; (II) the development of nematode soil food web indicators can provide information on the status of C and N retention and cycling in the reclaimed soil. Our results show that the PCS and RCS approaches reach similar conclusions, indicating a rapidly developing nematode soil food web during the first four years after reclamation. They also suggest that the nematode faunal profile may indicate the status of C and N retention and cycling in reclaimed soil. Overall, it can be concluded that the PCS approach successfully predicts the temporal development of the nematode soil food web in loess-dominated reclaimed mining soils, even when there is a range of variability in soil components and management conditions. • Pseudo and real chronosequence showed similar food web developments in reclaimed soil. • Chronosequence conclusions were not confounded by natural and management variation. • Nematode faunal profile may indicate C and N retention and cycling status in reclaimed soil. [ABSTRACT FROM AUTHOR]

To address severe soil Pb and Cd contamination from anthropogenic activities, governments have implemented various environmental management measures. However, the extent to which these measures have constrained Pb and Cd accumulation in industrial and mining city soils remains unclear. Here, we investigated Pb and Cd accumulation patterns in soils of Panzhihua City, Southwest China, and determined their dominant anthropogenic drivers using Pb and Cd isotopes. Pb accumulation initially slowed and then increased, while Cd showed a continuous acceleration. Traffic and coal-burning power generation were the dominant anthropogenic forcings for Pb and Cd accumulation in the soils, respectively. Environmental protection measures, particularly the ban on leaded gasoline, significantly reduced Pb accumulation by decreasing traffic-related Pb contributions to soils from 1980 to 2008. However, environmental management measures could not practically mitigate Cd accumulation in the soils owing to the high Cd content in consumed coal, poor efficiency of air pollutant control measures, and steep rise in coal-burning power generation. This study thus indicates the criticality of controlling Cd emissions from thermal power generation. Additionally, the challenges faced by small industrial and mining cities during economic transformation and environmental policy implementation warrant more attention. [Display omitted] • Pb accumulation initially slowed and then increased. • Cd accumulation showed a continuous acceleration. • Traffic was the dominant source of Pb in the soils. • Power generation was the leading cause of the accelerated Cd accumulation. • Environmental protection measures mitigate Pb but not Cd accumulation. [ABSTRACT FROM AUTHOR]

Forest ecology has a significant impact on soil total organic carbon (TOC) pool because of alterations in substrate induced changes in soil enzymatic activity and microbial diversity. We investigated impacts of poplar (Populus deltoides) chronosequence on organic C pool and its metabolic potential to predict changes induced by altered microbial diversity in semiarid ecosystems of Indian lower Himalayas. The present study integrates metagenomics to quantitatively appraise the bacterial communities in response to enzymatic activities and build-up of organic C in soils under poplar chronosequence (6-years, cycle-1; 12-years, cycle-2 and 18-years, cycle-3) established in lower Himalayas. Chronosequence of poplar-based agroforestry significantly (p <0.05) increased the TOC pool by ∼27.2–43.3%, while C build-up was manifested by a significant increase in soil related glomalin protein (TG) by ∼17.2–44.4% after completion of cycle-3, compared with the shorter chronosequence. Amongst different soil enzymatic activity, CM Case activity varied between 37.5 and 47.5 µg glucose g−1 soil hr−1; Fpase activity between 7.11 and 9.55 µg glucose g−1 soil hr−1 and dehydrogenase (DHA) between 27.6 and 35.1 µg TPF g−1 soil hr−1 in soils under different poplar-based chronosequence. Amongst the different chronosequence, soil protein varied between 349.6 and 475.0 µg protein g−1 soil, while fungal biomass between 395.7 and 527.8 µg n-acetyl glucosamine g−1 soil in soils under different poplar-based chronosequence. Total organic C, fungal biomass and microbial protein exhibited a significant relationship with xylanase, exocellulase, and β-glucosidase activity in soils. Poplar chronosequence (cycle-2 and cycle-3) exhibited a consistent linear increase in α-diversity of microbial taxonomy and microbial diversity at phylum, genus and species level. The microbial taxonomical structure and composition revealed that Actinobacteria , Chloroflexi , Planctomycetes , Firmicutes and Proteobacteria were largely affected by poplar chronosequence due to increased eubacterial community diversity. These results significantly improved our understanding of soil C cycling in soils under poplar based agroforestry in semiarid ecosystems in context of climate change by focusing on soil microbial C metabolic potentials and biological properties. These results suggest that poplar chronosequence are the main regulatory factors of bacterial diversity and microbial C metabolism processes, and can potentially play a central role in mediating the stability of C pool. This study contributed to a better understanding of the response of soil microbial community and C metabolic potentials. Therefore, implementing policies for promotion and adoption of poplar-based agroforestry practices can contribute to climate change mitigation efforts by fostering soil C sequestration and resilience in agricultural landscapes. • Poplar chronosequence significantly impacts organic C pool, enzyme activity and microbial diversity. • Popular chronosequence altered the bacterial diversity composition. • TOC pool increased significantly (27.2–43.3%) with successive duration of poplar establishment. • TOC exhibited significant relationship with xylanase, exocellulase, and β-glucosidase. • A linear increase in α-diversity of microbial taxonomy and microbial diversity was observed after second cycle of poplar. [ABSTRACT FROM AUTHOR]

Coastal reclamation has been used widely to accommodate urbanization and support increasing food demand. However, the responses of soil properties and soil-related ecosystem services (SES) to reclamation remain unclear. There are no effective operational methods for calculating the SES provided by reclaimed cropland. Using field sampling data of soil properties, we proposed a framework to evaluate the influence of reclamation on the soil's ability to provide five SESs: plant growth support (SES1), carbon storage (SES2), nutrient cycling (SES3), erosion control (SES4), and habitat provision (SES5). A series of SES indices were constructed accordingly and tested using data from a reclaimed soil chronosequence over 700 years in Hangzhou Bay, China. The results showed that all the SES indices increased significantly along the reclamation chronosequence, with the highest impact for SES2 (273.7% of soil C storage growth) owing to long-term continuous cultivation and fertilization. Most of the indices have a different logarithmic relationship with reclamation time, with a faster growth rate in the first 50 years, while SES1 increases linearly with reclamation time. Using soil organic matter as a reference, the sensitivity of SESs to reclamation is SES4 > SES2 > SES5 > SES3 > SES1. The significant positive correlations between all SES indices suggest that the provision of the five SESs is interdependent, with strong synergy. Our methods and index system can be effectively used to monitor coastal cropland protection and promote sustainable management of reclaimed land. • A framework was proposed to assess the impact of coastal reclamation on soil-related ecosystem services (SES). • Soil properties and SES were analyzed in a chronosequence of coastal reclamation. • SES increased with reclamation time in Hangzhou Bay. • Significant positive correlations between SESs indicated they have strong synergies. [ABSTRACT FROM AUTHOR]

A central question in carbon research is how stabilization mechanisms in soil change over time with soil development and how this is reflected in qualitative changes in soil organic matter (SOM). To address this matter, we assessed the influence of soil geochemistry on bulk SOM composition along a soil chronosequence in California, USA, spanning 3 million years. This was done by combining data on soil mineralogy and texture from previous studies with additional measurements on total carbon (C), stable isotope values (δ13 C and δ15 N), and spectral information derived from diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). To assess qualitative shifts in bulk SOM, we analysed the peak areas of simple plant-derived (S-POM), complex plant-derived (C-POM), and predominantly microbial-derived organic matter (OM; MOM) and their changes in abundance across soils with several millennia to millions of years of weathering and soil development. We observed that SOM became increasingly stabilized and microbial-derived (lower C : N ratio, increasing δ13 C and δ15 N) as soil weathering progressed. Peak areas of S-POM (i.e. aliphatic root exudates) did not change over time, while peak areas of C-POM (lignin) and MOM (components of microbial cell walls (amides, quinones, and ketones)) increased over time and depth and were closely related to clay content and pedogenic iron oxides. Hence, our study suggests that with progressing soil development, SOM composition co-varied with changes in the mineral matrix. Our study indicates that structurally more complex OM compounds (C-POM, MOM) play an increasingly important role in soil carbon stabilization mechanisms as the mineral soil matrix becomes increasingly weathered. [ABSTRACT FROM AUTHOR]

Glaciers are among the least explored environments on Earth, especially from a perspective of nutrient stoichiometry. Here, we documented and compared the nutrient concentrations and stoichiometric ratios in six distinct habitats of a glacier terminus in the source area of the Yangtze River, including surface ice (SI), basal ice (BI), basal sediment (BaS), newly exposed forefront soil close to glacial terminus (TS), soil at increasing distances from glacier terminus (DS), and soil with well-developed vegetation (VS). The results showed that SI had higher dissolve organic carbon (DOC) and nitrogen (N) concentrations as well as higher C:P (carbon:phosphorus) and N:P ratios than BI. However, BI had higher soluble reactive P (SRP) than SI. In addition, both SI and BI had very high C:P and N:P ratios, suggesting P-limitation. For sediment/soil along the chronosequence, total N (TN) and organic carbon (SOC) concentrations were lower in BaS, TS, and DS than in VS. Moreover, SRP concentration was higher in BaS and VS than in TS and DS. These nutrient patterns could be explained by differences in biotic influence in soil development or by changes in soil physical properties. With regard to nutrient stoichiometry, BaS, TS, and DS had low SOC:TN ratios but high dissolved inorganic N (DIN):SRP ratios. Considering both nutrient concentrations (high SOC and N but very low SRP) and stoichiometric ratios (low SOC:TN but high DIN:SRP), our data support an interpretation that P-limitation is dominant along the entire chronosequence following deglaciation. Considering that glaciers are experiencing severe retreat, this study can further our understanding and prediction of global biogeochemical cycles under future climate change. [ABSTRACT FROM AUTHOR]

Mineral weathering in soils is expected to promote chemical and physical interactions between soil organic matter and mineral phases, which are known to enhance the protection of organic matter from decomposition. The investigation of mineral-organic associations (MOAs) formation during weathering is therefore crucial to understanding carbon storage processes in soils. Until now studies have been mainly conducted by building inferences from soil characteristics, through short-term laboratory experiments in simplified conditions, or over very long-term time scales using soil chronosequences. Weathering can significantly alter the mineral matrix at the annual timescale, but knowledge regarding MOA formation processes occurring in situ , over short time scales and during the first stage of mineral weathering is lacking. To fill this gap, we performed a mesh bag incubation containing large Na-saturated and organic carbon-free vermiculite particles (200–400 µm in size) in acidic soil of a Douglas-fir forest, in the Beaujolais area (France). The vermiculite bags were deposited at the interface between the forest floor and the mineral soil, where intense weathering occurs. After 20 years of soil incubation, the weathered vermiculite particles were collected and characterized at the macroscale (X ray diffraction and physicochemical analyses), at the microscale (scanning electron microscopy-SEM imaging and element mapping) and at the nanoscale (transmission electron microscopy-TEM imaging, element mapping and speciation by electron energy loss spectroscopy-EELS) on a focus ion beam (FIB) section exposing the inside section of vermiculite particles. Cation exchange capacity, exchangeable cations and elemental analysis of the vermiculite particles showed important changes after 20 years of incubation. The initial exchangeable Na pool was completely depleted. The cation exchange capacity strongly decreased from 178.1 cmol c kg−1 to 49.2 cmol c kg−1 due to interlayer hydroxylation of the weathered vermiculite. The weathering budget indicated a 10% vermiculite dissolution and an organic carbon (C) enrichment of 5 mg g−1. Microscope images and elemental mapping of control vermiculite particles (nonincubated) showed a flat, smooth surface morphology with no detected C. In contrast, 20-year weathered vermiculite particles showed irregular outer- and inner-surfaces marked by multiple cracks from chemical dissolution. Some nano- and microscale exfoliation spaces filled with C were observed inside the weathered particles. C in association with Ca occurred in nanoscale exfoliation spaces. C also occurred entrapped in nanocrystalline Mn oxides (hausmannite) or K-rich aluminosilicates, which precipitated in micro-sized exfoliation spaces. These observations indicated that C storage inside the altered vermiculite particles was both mediated by chemical binding and physical entrapment. The functional groups of the organic matter revealed by EELS spectroscopy strongly differed between nano- and microscale exfoliation spaces. This study using the mineral bag incubation method provides evidence of new processes driving C storage inside large phyllosilicate particles during their initial and recent weathering, which could contribute to long-term C stabilization. [ABSTRACT FROM AUTHOR]

Soil carbon losses to the atmosphere, via soil heterotrophic respiration, are expected to increase in response to global warming, resulting in a positive carbon-climate feedback. Despite the well-known suite of abiotic and biotic factors controlling soil respiration, much less is known about how the magnitude of soil respiration responses to temperature changes over soil development and across contrasting soil properties. Here we investigated the role of soil development stage and soil properties in driving the responses of soil heterotrophic respiration to temperature. We incubated soils from eight chronosequences ranging in soil age from hundreds to million years, and encompassing a wide range of vegetation types, climatic conditions and chronosequences origins, at three assay temperatures (5 °C, 15 °C and 25 °C). We found a consistent positive effect of assay temperature on soil respiration rates across the eight chronosequences evaluated. However, chronosequences parent materials (sedimentary/sand dunes or volcanic) and soil properties (pH, phosphorus content and microbial biomass) determined the magnitude of this temperature effect. Finally, we observed a positive effect of soil development stage on soil respiration across chronosequences that did not alter the magnitude of assay temperature effects. Our work reveals that key soil properties alter the magnitude of the positive effect of temperature on soil respiration found across ecosystem types and soil development stages. This information is essential to better understand the magnitude of the carbon-climate feedback and thus to establish accurate greenhouse gas emission targets. [ABSTRACT FROM AUTHOR]

The intensive use of land has accelerated the loss of soil quality, a process that can be avoided by adopting conservationist production systems, such as the Integrated Crop-Livestock-Forest (CLFI system). It is noteworthy that in the Southwest of the State of Maranhão a substantial portion of soils in rural properties are degraded and in distinct stages of erosion, since they have been exploited for decades with non-properly managed pastures. Therefore, the objective of this work was to emphasize the importance of physical and chemical changes in the soil of pastures under crop-livestock-forest integration in general and in the Amazon region of state of Maranhão, Brazil. Therefore, a literature review was conducted through a search for studies in the Google Scholar database, which encompasses multiple other databases, such as Scielo, Elsevier, Scopus, Capes, and others. In face of the conditions of degradation in pastures throughout the state of Maranhão and the broad distribution of native forests such as Babassu forests, the use of technology from CLFI systems could allow for their recovery and sustainable status by means of economically and ecologically feasible productivity. Research on this field is therefore necessary to highlight short-and long-term efficiencies regarding carbon sequestration and quality of organic matter on the soil. [ABSTRACT FROM AUTHOR]

At the early stages of pedogenesis, the dynamics of phosphorus (P) in soils are controlled by microbial communities, the physicochemical properties of the soil and the environmental conditions. While various microorganisms involved in carrying out biogeochemical processes have been identified, little is known about the actual contribution of microbial processes, such as organic P hydrolysis and microbial P turnover, to P cycling. We thus focused on processes driven by microbes and how they affect the size and cycling of organic and inorganic soil P pools along a soil chronosequence in the Chamser Kangri glacier forefield (Western Himalayas). The rapid retreat of the glacier allowed us to study the early stages of soil formation under a cold arid climate. Biological P transformations were studied with the help of the isotopic composition of oxygen (O) in phosphate (δ18 O P) coupled to sequential P fractionation performed on soil samples (0–5 cm depth) from four sites of different age spanning 0 to 100–150 years. The P bound to Ca, i.e., 1 M HCl-extractable P, still represented 95 % of the total P stock after approximately 100 years of soil development. Its isotopic composition was similar to the parent material at the most developed site. Primary phosphate minerals, possibly apatite, mostly comprised this pool. The δ18 O P of the available P and the NaOH-extractable inorganic P instead differed from that of the parent material, suggesting that these pools underwent biological turnover. The δ18 O P of the available P was mostly controlled by the microbial P, suggesting fast exchanges occurred between these two pools possibly fostered by repeated freezing–thawing and drying–rewetting cycles. The release of P from organic P becomes increasingly important with soil age, constituting one-third of the P flux to available P at the oldest site. Accordingly, the lighter isotopic composition of the P bound to Fe and Al oxides at the oldest site indicated that this pool contained phosphate released by organic P mineralization. Compared to previous studies on early pedogenesis under alpine or cold climate, our findings suggest a much slower decrease of the P-bearing primary minerals during the first 100 years of soil development under extreme conditions. However, they provide evidence that, by driving short-term P dynamics, microbes play an important role in controlling the redistribution of primary P into inorganic and organic soil P pools. [ABSTRACT FROM AUTHOR]

A central question in carbon research is how stabilization mechanisms in soil change over time with soil development and how this is reflected in qualitative changes of soil organic matter (SOM). To address this matter, we assessed the influence of soil geochemistry on bulk SOM composition along a soil chronosequence in California, USA spanning 3 million years. This was done by combining data on soil mineralogy and texture from previous studies with additional measurements on total carbon (C), stable isotope values δ13C and δ15N), and spectral information derived from Diffuse Reflectance Infrared Fourier-Transform Spectroscopy (DRIFTS). To assess qualitative shifts in bulk SOM, we analysed the peak areas of simple plant-derived (S-POM), complex plant-derived (C-POM), and predominantly microbially derived OM (MOM) and their changes in abundance across soils varying several millennia to millions of years in weathering and soil development. We observed that SOM became increasingly stabilized and microbially-derived (lower C:N ratio, increasing δ1C and δ1N) as soil weathering progresses. Peak areas of S-POM (i.e. aliphatic root exudates) did not change over time, while peak areas of C-POM (lignin) and MOM (components of microbial cell walls (amides, quinones, and ketones)) increased over time and depth and were closely related to clay content and pedogenic iron oxides. Hence, our study suggests that with progressing soil development, SOM composition co-varies with changes in the mineral matrix. Our study indicates that a discrimination in favour of structurally more complex OM compounds (C-POM, MOM) gains importance as the mineral soil matrix becomes increasingly weathered. [ABSTRACT FROM AUTHOR]

Changes in the macro-, meso-, and micromorphological properties of plowed migration-mycelial chernozems (Haplic Chernozems) after their conversion into permanent unmanaged fallow state are discussed. The research objects are located in Kursk oblast. The results of the study indicate that changes in the soil morphology are most pronounced in the plow and carbonate-accumulative horizons. As a result of self-restoration processes, the structure of plow horizons improves, and their color becomes darker. Cracks formed as a result of seasonal soil drying disappear, and the structural degradation of plowed soils is stopped. Hard carbonate nodules formed in deep horizons of plowed soils due to seepage and stagnation of moisture in cracks in the periods of bare land disappear over 25–50 years of fallowing. Transitional forms—relatively soft calcareous nodules (beloglazka, white eyes) with a hard core—may be formed. Upon the uptake of soil solutions by roots, the accumulation of carbonates in the form of fibrous calcite takes place in the humus-containing material around the roots. Carbonate incrustations consisting of fibrous calcite are seen along cracks in plowed soils and in young fallows and are thin and fragmentary in the soils of old fallows and in virgin chernozem. The results of the studies of chronosequences of fallowed soils in Belgorod, Rostov, Lipetsk, and Kursk oblasts are generalized. The main features of transformation of the carbonate status of fallow soils are specified: (a) disappearance of hard carbonate pedofeatures in the lower soil horizons, (b) lowering of the lines of effervescence, and (c) a general decrease in the content and total pool of carbonate carbon. The change in the humus state of fallowed soils after the end of plowing are differently directed: the content of stock of humus decrease in gray soils (Phaeozems) and increase in chernozems and dark gray soils. [ABSTRACT FROM AUTHOR]

Today, there is a greater appreciation for the importance of the physical protection of carbon (C) through interactions with mineral surfaces, isolation from microbes, and the important role of transport in shaping soil properties and controlling moisture limitations on decomposition. As our paradigm for soil organic carbon (SOC) preservation changes, so too should our representation of the underlying processes in soil models. Reactive transport models (RTMs) provide a framework capable of assessing the interactive influence of soil chemistry and transport processes on the accumulation and turnover of SOC. In this study, we present new developments in the isotopically enabled RTM "CrunchTope," which is capable of explicitly tracking the three isotopes of carbon (12C, 13C, and 14C) and their fractionation between multiple coexisting and interacting solid, liquid and gas phases. This modeling framework opens the door to new applications of depth-resolved RTMs models in application to SOC and deeper subsurface carbon reservoirs. Here, we demonstrate SOC accumulation and radiocarbon aging for long-timescale models of soil development in CrunchTope. Our goal is to assess advantages and limitations of such an approach and to identify the type and complexity of reaction networks that are required to adequately apply this model to SOC dynamics. We assess the behavior of this model relative to a high-resolution dataset of SOC content, stable isotope composition, and radiocarbon ages as well as physical and hydrologic data measured from a chronosequence of soils located near Santa Cruz, California. Starting from a previously published model using a simplified reaction network with a single class of carbon, we sequentially incorporate multiple C reservoirs subject to both reactivity and transport pathways. Our results indicate that multiple SOC pools with different mean ages of C do not inherently emerge as a result of including reactions which are conventionally expected to provide a diversity of transit times, i.e., sorption and complexation of SOC on mineral surfaces. Instead, transit times emerge as a result of the timescales of the reactions represented in the reaction network. For mineral associated C, the RTM framework imposes dynamic equilibrium with the fluid phase dissolved organic C, such that no distinction in radiocarbon ages is achieved between these pools. Aged C can be produced by including a solid-phase C reservoir, with a rate-limited solubilization coefficient. Aging of SOC in this way is more akin to selective preservation than to mineral protection and, while such a mechanism may be at play in many soils, mineral protection is thought to be at least as important. As such, our results indicate that additional parameterization is required to reproduce the heterogeneity of carbon transit times that result from organo-mineral interactions. These efforts show the promise of a modeling approach where the varied transit time of soil C emerges from the dynamic physical and hydrologic properties of the model rather than from the a priori assignment of operationally defined pools. [ABSTRACT FROM AUTHOR]

Freeze–thaw (FT) events exert a great physiological stress on the soil microbial community and thus significantly impact soil biogeochemical processes. Studies often show ambiguous and contradicting results, because a multitude of environmental factors affect biogeochemical responses to FT. Thus, a better understanding of the factors driving and regulating microbial responses to FT events is required. Soil chronosequences allow more focused comparisons among soils with initially similar start conditions. We therefore exposed four soils with contrasting organic carbon contents and opposing soil age (i.e., years after restoration) from a postmining agricultural chronosequence to three consecutive FT events and evaluated soil biochgeoemical responses after thawing. The major microbial biomass carbon losses occurred after the first FT event, while microbial biomass N decreased more steadily with subsequent FT cycles. This led to an immediate and lasting decoupling of microbial biomass carbon:nitrogen stoichiometry. After the first FT event, basal respiration and the metabolic quotient (i.e., respiration per microbial biomass unit) were above pre-freezing values and thereafter decreased with subsequent FT cycles, demonstrating initially high dissimilatory carbon losses and less and less microbial metabolic activity with each iterative FT cycle. As a consequence, dissolved organic carbon and total dissolved nitrogen increased in soil solution after the first FT event, while a substantial part of the liberated nitrogen was likely lost through gaseous emissions. Overall, high-carbon soils were more vulnerable to microbial biomass losses than low-carbon soils. Surprisingly, soil age explained more variation in soil chemical and microbial responses than soil organic carbon content. Further studies are needed to dissect the factors associated with soil age and its influence on soil biochemical responses to FT events. [ABSTRACT FROM AUTHOR]

Plant–soil feedbacks (PSFs) are often involved in fundamental ecological processes such as plant succession and species coexistence. After a plant initiating PSFs dies, legacies of PSFs occurring as soil signatures that influence subsequent plants could persist for an unknown duration. Altered resource environments following plant death (especially light availability) could affect whether legacy effects manifest and persist. To evaluate PSFs and their legacies, we obtained soils from a chronosequence of Prunus serotina harvests. In a greenhouse experiment, we planted conspecific seedlings under two light levels in these soils of varying time since the influence of live Prunus serotina, and compared seed/seedling survival in soils from live trees, stumps, and surrounding forest matrix within each site and across the chronosequence. PSF legacies were measured as the difference between seedling performance in live tree and stump soils within a site. Negative PSF legacies of P. serotina were short-lived, lasting up to 0.5 years after tree removal. These effects occurred under 5% but not 30% full sun. PSFs and their legacies manifested in seed/seedling survival, but not biomass. Though restricted to low light, short-lived legacies of P. serotina PSFs could have lasting impacts on plant community dynamics during post-disturbance regeneration by disfavoring P. serotina regeneration in small tree-fall gaps. [ABSTRACT FROM AUTHOR]

Since the last glacial maximum, soil formation related to ice‐cover shrinkage has been one major sink of carbon accumulating as soil organic matter (SOM), a phenomenon accelerated by the ongoing global warming. In recently deglacierized forelands, processes of SOM accumulation, including those that control carbon and nitrogen sequestration rates and biogeochemical stability of newly sequestered carbon, remain poorly understood. Here, we investigate the build‐up of SOM during the initial stages (up to 410 years) of topsoil development in 10 glacier forelands distributed on four continents. We test whether the net accumulation of SOM on glacier forelands (i) depends on the time since deglacierization and local climatic conditions (temperature and precipitation); (ii) is accompanied by a decrease in its stability and (iii) is mostly due to an increasing contribution of organic matter from plant origin. We measured total SOM concentration (carbon, nitrogen), its relative hydrogen/oxygen enrichment, stable isotopic (13C, 15N) and carbon functional groups (C‐H, C=O, C=C) compositions, and its distribution in carbon pools of different thermal stability. We show that SOM content increases with time and is faster on forelands experiencing warmer climates. The build‐up of SOM pools shows consistent trends across the studied soil chronosequences. During the first decades of soil development, the low amount of SOM is dominated by a thermally stable carbon pool with a small and highly thermolabile pool. The stability of SOM decreases with soil age at all sites, indicating that SOM storage is dominated by the accumulation of labile SOM during the first centuries of soil development, and suggesting plant carbon inputs to soil (SOM depleted in nitrogen, enriched in hydrogen and in aromatic carbon). Our findings highlight the potential vulnerability of SOM stocks from proglacial areas to decomposition and suggest that their durability largely depends on the relative contribution of carbon inputs from plants. [ABSTRACT FROM AUTHOR]

The area of Burdur Lake gradually decreased from 211 to 122 km2 between 1975 and 2021. In this study, we explored the effects of time, environmental factors, and land uses on the spatial distribution of soil chemical properties (SOC, CaCO 3 , EC, and pH). In total 240 soil samples were taken (0–20 cm depth) at a 400 × 400 m grid sampling in the former lakebed, pasture, and agricultural fields representing a chronosequence. We found a considerable temporal and topographic trend in SOC, CaCO 3 , EC, pH, and vegetation density. The SOC, EC, and pH were higher in younger soils. Land use significantly affected soil properties. Natural vegetation species mainly grew in the pasture but only sparsely in the former lakebed areas. Salt-affected and alkaline soils and exposure time affected the density and spatial distribution of vegetation in the former lakebed and pasture areas. We tested different models to spatially predict soil properties and found that random forest had higher prediction accuracy for SOC (r2 = 0.50) and CaCO 3 (r2 = 0.36), whereas the cubist model had higher prediction accuracy for EC (r2 = 0.60) and pH (r2 = 0.38). We conclude that the vegetation density and distribution of SOC, CaCO 3 , EC, and pH were controlled by topography, time, and land use. The time and space-for-time substitution approach can be used to study soil chronosequence and biosequence in areas with shrinking lakes. [ABSTRACT FROM AUTHOR]

• The SOC stocks in the 0–500 cm soil depth varied from 174.5 − 213.2 Mg C/ha. • TAFS store 39–46 % the SOC stocks in the 100–500 cm soil depths. • 50–58 % of the P stocks were stored in the 100–500 cm soil depths. • Tea agroforestry systems store a significant amount of carbon in their deeper soil. Due to the rapid growth of the tea industry, the tea plantation area has steadily increased worldwide. In some regions, croplands and natural forests have been converted into tea plantations causing habitat fragmentation, reducing landscape connectivity and loss of biodiversity. On the other hand, ancient tea forests, rustic tea and tea agroforestry have been shown to support higher native biodiversity. However, there is a dearth of information on the potential of tea agroforestry systems (TAFS) to store soil organic carbon (SOC) and nutrients in deeper soil layers. For the first time, here we provide estimates of concentrations and stocks of SOC and available nitrogen (N), phosphorus (P) and potassium (K) in deep soils in a chronosequence of tea agroforestry and adjacent natural forest stands. The concentrations of SOC, available N, P and K steadily decreased with soil depth across all the chronosequence of TAFS and natural forest stands. The SOC stocks in the 0–500 cm soil depth varied from 174.5 Mg C/ha in 20 years old TAFS to 213.2 Mg C/ha in 60 years old TAFS and 311 Mg C/ha in natural forest stands. Based on the empirical data, we propose the following predictive models for estimation of deep SOC concentrations (Y): Y = 0.55 + 14.67 e - 0.013 D in TAFS and Y = 1.04 + 31.53 e - 0.014 D in natural forests. The highest available N stocks were found in 60 years old TAFS (181.7 kg ha−1) while the available P and K stocks were highest in the forest soils (22.42 kg ha−1 and 56.86 kg ha−1). As in SOC, clay content and the SOC: clay ratios declined with soil depth in all the land uses studied. The SOC: clay ratios indicated a good soil structure in the study sites. It is concluded that TAFS store 39–46 % the SOC stocks and over 50 % of the available N, P and K stocks in the 100–500 cm soil depths. The predictive models developed here could be used for estimating deep soil SOC stocks after validation with independent datasets. [ABSTRACT FROM AUTHOR]

The restoration of plants is effective for restoring ecosystems in eroded areas. Soil bacterial communities play an important role in nutrient cycling. High-throughput sequencing technology was used to determine the changes in soil bacteria in different restored plant communities and years of restoration. The FAPROTAX database and random forest model were also used to analyze the changes in soil bacterial carbon (C), nitrogen (N), and phosphorus (P) metabolic functions and their influencing factors. The results showed that the bacterial community diversity, soil texture, physicochemical properties, and multifunctionality improved substantially with the increments and years of restoration. These changes, in turn, altered the nutrient metabolic functions in soils by increasing the fixation of bacterial C, decreasing the fixation of N, and gradually relieving the limitations on N. However, these changes also increased the limitation of P during the late stage of restoration. The pH values and soil nutrients were crucial and exerted a large influence on the nutrients and metabolic functions of the bacteria. These findings facilitate the restoration of plants in subtropical areas of eroded soil. [ABSTRACT FROM AUTHOR]