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Purpose: Subtropical lake riparian ecosystems experience seasonal water table fluctuations and increased nitrogen (N) deposition with changing N composition. However, the interplay of soil water content (SWC), N deposition chemical composition, and their interaction on plant growth through regulating N acquisition remains poorly understood. Methods: In this controlled experiment with a sedge species Carex thunbergii, we investigated two treatment factors: (1) SWC at 100%, 60%, and 30% of field capacity, combined with (2) N treatments with NH4+:NO3− ratios of 1:3, 2:2, and 3:1. Treatment verifications were conducted using 15N isotope tracer (15NH4NO3 and NH415NO3) technology. Results: Results showed a notable trend of reduced biomass of C. thunbergii with increasing NH4+: NO3− ratio, especially under high SWC conditions. This negative effect of a high NH4+: NO3− ratio on plant biomass accumulation also aligned with reduced N use efficiency (NUE). Conversely, C. thunbergii exhibited accelerated N uptake with increasing SWC, with the most pronounced response observed in the treatment of NH4+: NO3− ratio of 3:1. Principal component analyses provided evidence for SWC-dominated functional coordination between plant below- and aboveground parts in mediating plant N acquisition, while correlation analyses revealed that NUE mainly contributed to belowground productivity of C. thunbergii. Conclusions: Our findings suggest that manipulating water table (as a proxy of SWC) and managing soil NH4+: NO3− ratios could optimize the productivity of this sedge species in riparian ecosystem. The coordination of leaf-root trait highlights the necessity to integrate above- and belowground traits for a comprehensive understanding of plant N acquisition strategies. Understanding plant N acquisition and use efficiency may help us better predict the potential impacts of future climate change components on ecosystem functions. [ABSTRACT FROM AUTHOR]

As the carbon (C) credit market evolves, incorporating organic matter into soils has emerged as a key strategy in C farming. Soil heterotrophic respiration (RH) plays a pivotal role in maintaining the C balance in terrestrial ecosystems, yet the contrasting impacts of fresh and pyrogenic organic matter applications on soil RH, and associated underlying mechanisms, have not been fully investigated. Through a 2-year field experiment, we investigated how applying maize straw and its derived biochar affect the physical, chemical, and microbial properties of soil in a subtropical Moso bamboo forest. Results showed that straw application increased soil RH, while biochar application suppressed it. Soil RH was correlated positively with β-glucosidase and cellobiohydrolase activities but negatively with RubisCO enzyme activity. Increased soil RH under straw application was linked to the increased β-glucosidase/cellobiohydrolase activities driven by elevated water-soluble organic C and O-alkyl C levels as well as GH48 and cbhI gene abundances, and the decreased RubisCO enzyme activity caused by reduced cbbL gene abundance. Conversely, reduced soil RH under biochar application was linked to reductions in β-glucosidase and cellobiohydrolase activities induced by increased aromatic C and decreased GH48 and cbhI gene levels, and increases in RubisCO enzyme activity driven by higher cbbL gene abundance. More importantly, changes in soil RH were clearly linked to microbial dynamics. Specifically, increases in the relative abundances of Alphaproteobacteria and Sordariomycetes and decreases in AD3 and Tremellomycetes contributed to the enhanced soil RH under straw application. With biochar application, the reverse effect occurred, ultimately contributing to the reduced soil RH. Our study demonstrates that maize straw application increases while biochar application decreases soil RH in the subtropical forest. These findings reveal that biochar reduced soil RH through changing microbial activity in subtropical forests, providing insight into complex dynamics of soil C cycling in response to diverse interventions. [ABSTRACT FROM AUTHOR]

Background: Precipitation plays an important role in crop production and soil greenhouse gas emissions. However, how crop yield and soil nitrous oxide (N2O) emission respond to precipitation change, particularly with different background precipitations (dry, normal, and wet years), has not been well investigated. In this study, we examined the impacts of precipitation changes on corn yield and soil N2O emission using a long-term (1981–2020, 40 years) climate dataset as well as seven manipulated precipitation treatments with different background precipitations using the DeNitrification-DeComposition (DNDC) model. Results: Results showed large variations of corn yield and precipitation but small variation of soil N2O emission among 40 years. Both corn yield and soil N2O emission showed near linear relationships with precipitation based on the long-term precipitation data, but with different response patters of corn yield and soil N2O emission to precipitation manipulations. Corn yield showed a positive linear response to precipitation manipulations in the dry year, but no response to increases in precipitation in the normal year, and a trend of decrease in the wet year. The extreme drought treatments reduced corn yield sharply in both normal and wet years. In contrast, soil N2O emission mostly responded linearly to precipitation manipulations. Decreases in precipitation in the dry year reduced more soil N2O emission than those in the normal and wet years, while increases in precipitation increased more soil N2O emission in the normal and wet years than in the dry year. Conclusions: This study revealed different response patterns of corn yield and soil N2O emission to precipitation and highlights that mitigation strategy for soil N2O emission reduction should consider different background climate conditions. [ABSTRACT FROM AUTHOR]

Aims: Soil warming significantly influences soil organic carbon (SOC) pools in terrestrial ecosystems through its impact on the processes of carbon (C) input and decomposition as well as the stabilization of SOC pools. Most studies demonstrated that soil warming reduces SOC pools, but the magnitude is highly variable, and the underlying mechanisms are poorly understood. Methods: The concentration, stability (dissolved, particulate, and mineral-associated SOC) and source (plant-derived vs. microbial-derived) of SOC, soil microbial community composition, and enzymatic activities were studied in a 10-year soil warming field experiment in an East Asian monsoon forest. Results: 10-year soil warming significantly enhanced SOC in the top 0–10 cm soil. The increased SOC induced by warming was mainly derived from plants, with lignin and phenol markers increasing by 60% on average, accompanied by a 27% decrease in microbial-derived SOC. However, the overall effect of warming on SOC stability was not statistically significant. Conclusions: The results suggest that the moist monsoon forest soil could sequester SOC upon long-term warming. The discrepancy between our findings and those from other regions highlights an urgent need for a better understanding of how the contrasting effects of plant- and microbial-derived C mediate the response of the SOC pool to warming across biomes. [ABSTRACT FROM AUTHOR]

Background and aims: Understanding how altered precipitation patterns affect the dynamics of phosphorus (P) fractions in both soil and foliage is crucial for predicting climate-induced changes in plant growth and community structure, especially within tropical forests with P-impoverished soils.We conducted a nine-year precipitation experiment in a secondary tropical forest, simulating delayed (DW) and wetter wet season (WW) to reflect potential precipitation changes. We analyzed P fractions in soil (0–10 cm and 10–20 cm) and foliage of four dominant trees, and investigated the correlations among these P fractions and photosynthesis.DW treatment reduced soil P bioavailability and induced foliar P redistribution, while WW treatment increased soil pH and NH4+-N content but had little influence on soil P form. DW treatment generally reduced foliar total P levels and diminished various P fractions with notable species-specific disparities. Moreover, DW treatment variably reduced area-based photosynthetic carbon assimilation rates (Aarea), exhibiting species-specific effects, while WW treatment inconsistently elevated Aarea across species. The structural equation model revealed that Aarea was directly influenced by foliar P fractions and photosynthetic nutrient efficiency, and indirectly by precipitation treatment on soil properties and P fractions.Altered seasonal precipitation patterns affect soil bioavailable P forms and/or soil chemical properties, and thereby influence foliar P fractions allocation and photosynthesis of dominant trees. Soil and foliar P fractions responses to precipitation treatments varied across different sampling months, underscoring the complexity of P cycle and suggesting tree acclimation and resilience. These insights improve our understanding of climate effects on nutrient cycles and resilience.Methods: Understanding how altered precipitation patterns affect the dynamics of phosphorus (P) fractions in both soil and foliage is crucial for predicting climate-induced changes in plant growth and community structure, especially within tropical forests with P-impoverished soils.We conducted a nine-year precipitation experiment in a secondary tropical forest, simulating delayed (DW) and wetter wet season (WW) to reflect potential precipitation changes. We analyzed P fractions in soil (0–10 cm and 10–20 cm) and foliage of four dominant trees, and investigated the correlations among these P fractions and photosynthesis.DW treatment reduced soil P bioavailability and induced foliar P redistribution, while WW treatment increased soil pH and NH4+-N content but had little influence on soil P form. DW treatment generally reduced foliar total P levels and diminished various P fractions with notable species-specific disparities. Moreover, DW treatment variably reduced area-based photosynthetic carbon assimilation rates (Aarea), exhibiting species-specific effects, while WW treatment inconsistently elevated Aarea across species. The structural equation model revealed that Aarea was directly influenced by foliar P fractions and photosynthetic nutrient efficiency, and indirectly by precipitation treatment on soil properties and P fractions.Altered seasonal precipitation patterns affect soil bioavailable P forms and/or soil chemical properties, and thereby influence foliar P fractions allocation and photosynthesis of dominant trees. Soil and foliar P fractions responses to precipitation treatments varied across different sampling months, underscoring the complexity of P cycle and suggesting tree acclimation and resilience. These insights improve our understanding of climate effects on nutrient cycles and resilience.Results: Understanding how altered precipitation patterns affect the dynamics of phosphorus (P) fractions in both soil and foliage is crucial for predicting climate-induced changes in plant growth and community structure, especially within tropical forests with P-impoverished soils.We conducted a nine-year precipitation experiment in a secondary tropical forest, simulating delayed (DW) and wetter wet season (WW) to reflect potential precipitation changes. We analyzed P fractions in soil (0–10 cm and 10–20 cm) and foliage of four dominant trees, and investigated the correlations among these P fractions and photosynthesis.DW treatment reduced soil P bioavailability and induced foliar P redistribution, while WW treatment increased soil pH and NH4+-N content but had little influence on soil P form. DW treatment generally reduced foliar total P levels and diminished various P fractions with notable species-specific disparities. Moreover, DW treatment variably reduced area-based photosynthetic carbon assimilation rates (Aarea), exhibiting species-specific effects, while WW treatment inconsistently elevated Aarea across species. The structural equation model revealed that Aarea was directly influenced by foliar P fractions and photosynthetic nutrient efficiency, and indirectly by precipitation treatment on soil properties and P fractions.Altered seasonal precipitation patterns affect soil bioavailable P forms and/or soil chemical properties, and thereby influence foliar P fractions allocation and photosynthesis of dominant trees. Soil and foliar P fractions responses to precipitation treatments varied across different sampling months, underscoring the complexity of P cycle and suggesting tree acclimation and resilience. These insights improve our understanding of climate effects on nutrient cycles and resilience.Conclusion: Understanding how altered precipitation patterns affect the dynamics of phosphorus (P) fractions in both soil and foliage is crucial for predicting climate-induced changes in plant growth and community structure, especially within tropical forests with P-impoverished soils.We conducted a nine-year precipitation experiment in a secondary tropical forest, simulating delayed (DW) and wetter wet season (WW) to reflect potential precipitation changes. We analyzed P fractions in soil (0–10 cm and 10–20 cm) and foliage of four dominant trees, and investigated the correlations among these P fractions and photosynthesis.DW treatment reduced soil P bioavailability and induced foliar P redistribution, while WW treatment increased soil pH and NH4+-N content but had little influence on soil P form. DW treatment generally reduced foliar total P levels and diminished various P fractions with notable species-specific disparities. Moreover, DW treatment variably reduced area-based photosynthetic carbon assimilation rates (Aarea), exhibiting species-specific effects, while WW treatment inconsistently elevated Aarea across species. The structural equation model revealed that Aarea was directly influenced by foliar P fractions and photosynthetic nutrient efficiency, and indirectly by precipitation treatment on soil properties and P fractions.Altered seasonal precipitation patterns affect soil bioavailable P forms and/or soil chemical properties, and thereby influence foliar P fractions allocation and photosynthesis of dominant trees. Soil and foliar P fractions responses to precipitation treatments varied across different sampling months, underscoring the complexity of P cycle and suggesting tree acclimation and resilience. These insights improve our understanding of climate effects on nutrient cycles and resilience. [ABSTRACT FROM AUTHOR]

Atmospheric acid deposition remains a widespread problem that may influence the protection of carbon (C) in soil by altering organo-mineral interactions. However, the impacts of additional acidity on organo-mineral interactions and soil C sequestration in naturally acidic tropical soils with a high content of reactive iron (Fe) phases have not been well studied. Here we conducted a long-term (9.5-year) field experiment with a gradient of acidity treatments (3, 9.6, 32, 96 mol H+ ha−1 year−1 as nitric + sulfuric acid, added to ambient deposition) to examine how acidification alters organo-mineral interactions and soil organic carbon (SOC) pools in a tropical forest of China where soils are already highly acidic (pH ≈ 4). As expected, soil acidification significantly enhanced the leaching of base cations (e.g., Ca2+), and it also altered the solubility and composition of Fe and Al phases. The acidity treatments decreased total Fe and converted more crystalline Fe (oxyhydr) oxides to short-range-ordered phases, evidenced by an increase in Fe extracted by citrate-ascorbate solution and 0.5 M hydrochloric acid, and a decrease in the difference in Fe extracted by citrate-dithionite and citrate-ascorbate. Together, these changes led to a large increase in Fe-bound C versus a relatively small decrease in Ca-bound C. Overall, the acidity treatments increased the mineral-associated C stock to 32.5–36.4 Mg C ha−1 versus 28.8 Mg C ha−1 in the control, accounting for 71–83% of the observed increase in total SOC stock. These findings highlight the importance of pH-sensitive geochemical changes and the key roles of Fe in regulating the response of SOC to further inputs of acid deposition even in highly weathered and naturally acidic soils. The magnitude of SOC changes observed here further reveals the necessity of including pH-sensitive geochemistry in Earth system models to better predict ecosystem C budgets under future acid deposition scenarios. [ABSTRACT FROM AUTHOR]

Purpose: Glomalin-related soil protein (GRSP) is an essential component of soil organic C for maintaining soil quality and structure and plays a critical role in soil carbon (C) sequestration. However, how GRSP changes under nitrogen (N) deposition remains poorly understood. Materials and methods: We assessed total GRSP (T-GRSP) and easily extractable GRSP (EE-GRSP) under a control (no N input), low N addition (LN, 40 kg N ha−1 year−1), and high N addition (HN, 80 kg N ha−1 year−1) treatments in 2015 and 2016 in a Chinese fir (Cunninghamia lanceolata) plantation in the subtropical China. We also analyzed soil properties contents and explored the stoichiometric ratios of soil organic C (SOC), total N (TN), and total phosphorus (TP) with GRSPs. Results: Compared to the control, both T-GRSP and EE-GRSP were significantly reduced under the HN treatment, but had no significant difference under the LN treatment. The ratio of T-GRSP and EE-GRSP was reduced by the N addition. Soil organic C (SOC) and dissolved organic C (DOC) were significantly affected by N addition treatments. The ratios of GRSP-C to SOC and of EEGRSP-C to SOC ranged from 6.29 to 16.07% and 1.34 to 3.52%, respectively. T-GRSP and EE-GRSP were positively correlated with SOC/TN ratio, but negatively correlated with soil TN/TP and SOC/TP ratios. Conclusion: Our results indicated that the GRSP reductions under N deposition in soil are mediated by soil C, N, and P stoichiometry, and particularly, the reduction of EE-GRSP by DOC. This study improved our mechanistic understanding of dynamics of GRSPs under increasing N enrichment in subtropical plantation ecosystems. [ABSTRACT FROM AUTHOR]

Precipitation and nitrogen (N) fertilization are the two most important drivers for soil nitrous oxide (N2O) emission. However, the effects of changes in N fertilization and precipitation patterns (i.e., precipitation intensity and frequency) on N2O emissions in agricultural fields are still unclear. In this study, we simulated soil N2O emission under different precipitation patterns (6 precipitation intensities, and 12 precipitation frequencies by either merging or splitting precipitation events) and N fertilization rates (low, typical, and high N fertilization) in a cornfield using the DeNitrification-DeComposition model. The model was parameterized and validated using meteorological data and N experimental measurements in Nashville, Tennessee, USA. Results showed that soil water filled pore space (WFPS) and simulated soil N2O emission increased as precipitation intensity increased. Less frequent but high intensity precipitation treatments reduced the soil WFPS by 25.2% and stimulated soil N2O emission by 45.3%, while more frequent but low intensity precipitation treatments increased soil WFPS by 9.0% and reduced soil N2O emission by 23.9%. Compared to typical N fertilization, the sensitivity of soil N2O emission to precipitation was higher under high N than low N fertilization treatments, and the response ratios were 50.0% and 40.1%, respectively. There was significant interactive effect of precipitation intensity and N fertilization on soil N2O emission. These findings improved our understanding of precipitation and N impacts on soil N2O emissions and provided useful knowledge for irrigation and N fertilizer management in agriculture to mitigate greenhouse gas emissions. [ABSTRACT FROM AUTHOR]

Key message: Nutrient limitation changed from N–P co-limitation in the native shrubs to N limitation in the plantations. Element stoichiometry is a powerful tool to examine plant–soil nutrient feedbacks. In karst ecosystems, southwest China, afforestation has been widely adopted to restore soil fertility and enhance ecosystem functioning under degraded native shrub stands. However, it is unclear whether and how multiple-element stoichiometry of plants in afforested forests would differ from the native shrub community. We investigated the concentrations of C, N, S, P, K, Ca, Mg, Na, Fe, Al, Cu, Zn, and Mn in leaves and soils in native shrub community and three plantations (Pinus yunnanensis, Alnus japonica, and Platycladus orientalis). We found (1) There was significant discrimination in leaf elemental compositions between native shrub community and plantations in the karst region, southwest China. Native shrubs had lower leaf N, P, S and higher C, Ca, and Mg concentrations, as well as C:P and N:P ratios, compared to plantations; (2) For different plant species, grasses had higher P, K, and Na and lower C:P and N:K, compared to trees and shrubs; (3) N:P, K and S concentrations differed most between the native shrubs and plantations; (4) N:P in native shrubs was close to 12 while decreased to 11.3, 10.2 and 9.7 in three plantations. These results suggest that plantations strongly changed the elemental stoichiometry of native shrub communities in the karst region. N:P, Ca:Mg, K and S are key indicators for plant nutrient status in the study area. P limitation alleviates in plantations compared to native shrubs. Our study could be used to guide reforestation and improve ecosystem functioning in the karst region, Southwest China. [ABSTRACT FROM AUTHOR]

Grazing can affect plant community composition and structure directly by foraging and indirectly by increasing wind erosion and dust storms and subsequently influence ecosystem functioning and ecological services. However, the combined effects of grazing, wind erosion, and dust deposition have not been explored. As part of a 7-year (2010–2016) field manipulative experiment, this study was conducted to examine the impacts of grazing and simulated aeolian processes (wind erosion and dust deposition) on plant community cover and species richness in a temperate steppe on the Mongolian Plateau, China. Grazing decreased total cover by 4.2%, particularly the cover of tall-stature plants (> 20 cm in height), but resulted in 9.1% greater species richness. Wind erosion also reduced total cover by 17.0% primarily via suppressing short-stature plants associated with soil nitrogen loss, but had no effect on species richness. Dust deposition enhanced total cover by 5.7%, but resulted in a 7.3% decrease in species richness by driving some of the short-stature plant species to extinction. Both wind erosion and dust deposition showed additive effects with grazing on vegetation cover and species richness, though no detectable interaction between aeolian processes and grazing could be detected due to our methodological constraints. The changes in gross ecosystem productivity, ecosystem respiration, and net ecosystem productivity under the wind erosion and dust deposition treatments were positively related to aeolian process-induced changes in vegetation cover and species richness, highlighting the important roles of plant community shifts in regulating ecosystem carbon cycling. Our findings suggest that plant traits (for example, canopy height) and soil nutrients may be the key for understanding plant community responses to grassland management and natural hazards. [ABSTRACT FROM AUTHOR]

Allometric growth reflects different allocation patterns and relationships of different components or traits of a plant and is closely related to ecosystem carbon storage. As an introduced species, the growth and carbon storage of Sonneratia apetala are still unclear. To derive allometric relationships of the mangrove S. apetala and to estimate carbon storage in mangrove ecosystems, we harvested 12 individual Sonneratia apetala trees from four different diameter classes in the Futian National Nature Reserve, Guangdong, China. Allometric growth models were fitted. The results showed that diameter at breast height (DBH) and wood density were better variables for predicting plant biomass (including above- and below-ground biomass) than plant height. There were significant power function relationships between biomass and DBH, with a mean allometric exponent of 2.22, and stem biomass accounted for 97% of the variation in S. apetala total biomass. Nearly isometric scaling relationships were developed between stem biomass and other biomass components. To better understand the carbon stocks of the S. apetala ecosystem, we categorized all trees into five age classes and quantified vegetation carbon storage. The S. apetala vegetation carbon storage ranged from 96.48 to 215.35 Mg C ha−1, and the carbon storage significantly increased with stand age. The allometric equations developed in this study are useful to estimate biomass and carbon storage of S. apetala ecosystems. [ABSTRACT FROM AUTHOR]

Subtropical China has a large area of Acacia mangium plantations; however, some key aspects of the structural and functional changes and the associated mechanisms after planting are still not well understood. We established a permanent plot in an A. mangium plantation and monitored the plant diversity (i.e., the number of species), biomass, soil physical and chemical properties and light transmittance from 1984 to 2018. Protocols for standard observation and measurement of Chinese Ecological Research Network were adopted. The total number of species in the plantation increased gradually from 3 to 38 during the 34-year period. The biomass in the tree layer initially increased rapidly from 1.60 to 185.01 t/ha within 7 years and then slowly increased to 188.69 t/ha during the following 27 years. The soil fertility of the A. mangium plantation improved continuously over the 34-year period. Vegetation restoration had positive effects on soil properties, such as soil moisture, soil bulk density, soil organic matter and soil total nitrogen and available phosphorus contents. The structure (i.e., plant diversity and light transmittance) and function (i.e., biomass and soil fertility) of the A. mangium plantation were not restored synchronously after 34 years of development. However, considering that the tree species richness in the natural forests in this region was 134, this plantation has slowly transformed from plantation to a natural forest. Artificial intercropping with native tree species can facilitate succession to a natural forest. [ABSTRACT FROM AUTHOR]

Nitrogen (N) fertilizers can potentially alter spatial distribution of soil organic carbon (SOC) and total nitrogen (TN) concentrations in croplands such as switchgrass (SG: Panicum virgatum L.) and gamagrass (GG: Tripsacum dactyloides L.), but it remains unclear whether these effects are the same between crops and under different rates of fertilization. 13C and 15N are two important proxy measures of soil biogeochemistry, but they were rarely examined as to their spatial distributions in soil. Based on a three-year long fertilization experiment in Middle Tennessee, USA, the top mineral horizon soils (0–15 cm) were collected using a spatially explicit design within two 15-m2 plots under three fertilization treatments in SG and GG croplands. A total of 288 samples were collected based on 12 plots and 24 samples in each plot. The fertilization treatments were no N input (NN), low N input (LN: 84 kg N ha−1 in urea) and high N input (HN: 168 kg N ha−1 in urea). The SOC, TN, SOC/TN (C: N), δ13C and δ15N were quantified and their within-plot variations and spatial distributions were achieved via descriptive and geostatistical methods. Results showed that SG generally displayed 10~120% higher plot-level variations in all variables than GG, and the plot-level variations were 20~77% higher in NN plots than LN and HN plots in SG but they were comparable in unfertilized and fertilized plots in GG. Relative to NN, LN and HN showed more significant surface trends and spatial structures in SOC and TN in both croplands, and the fertilization effect appeared more pronounced in SG. Spatial patterns in C: N, δ13C and δ15N were comparable among different fertilization treatments in both croplands. The descending within-plot variations were also identified among variables (SOC > TN > δ15N > C: N > δ13C). This study demonstrated that N fertilizations generally reduced the plot-level variance and simultaneously re-established spatial structures of SOC and TN in bioenergy croplands, which little varied with fertilization rate but was more responsive in switchgrass cropland. [ABSTRACT FROM AUTHOR]

Changing precipitation regimes can profoundly affect plant growth in terrestrial ecosystems, especially in arid and semi-arid regions. However, how changing precipitation, especially extreme precipitation events, alters plant diversity and community composition is still poorly understood. A 3-year field manipulative experiment with seven precipitation treatments, including − 60%, − 40%, − 20%, 0% (as a control), + 20%, + 40%, and + 60% of ambient growing-season precipitation, was conducted in a semi-arid steppe in the Mongolian Plateau. Results showed total plant community cover and forb cover were enhanced with increased precipitation and reduced under decreased precipitation, whereas grass cover was suppressed under the − 60% treatment only. Plant community and grass species richness were reduced by the − 60% treatment only. Moreover, our results demonstrated that total plant community cover was more sensitive to decreased than increased precipitation under normal and extreme precipitation change, and species richness was more sensitive to decreased than increased precipitation under extreme precipitation change. The community composition and low field water holding capacity may drive this asymmetric response. Accumulated changes in community cover may eventually lead to changes in species richness. However, compared to control, Shannon–Weiner index (H) did not respond to any precipitation treatment, and Pielou's evenness index (E) was reduced under the + 60% treatment across the 3 year, but not in each year. Thus, the findings suggest that plant biodiversity in the semi-arid steppe may have a strong resistance to precipitation pattern changes through adjusting its composition in a short term. [ABSTRACT FROM AUTHOR]

Invasive plant species are often able to alter soils in a way that benefits their own fitness over that of native species. While interspecific competitions may drive species to acquire different forms of nitrogen (N) to avoid intensive competition, plant-mycorrhizal interactions can also influence plant nutrient acquisition. Yet, it is unclear whether a variation in N acquisition by an invasive species is driven by interspecific resource partitioning due to competition with native species or by its symbiosis with arbuscular mycorrhizal (AM) fungi. We conducted a pot experiment to examine the effects of competition and fungicide on the uptake of different N forms by Flaveria bidentis, an invasive plant having symbiotic relationships with AM fungi, and two coexisting native species, mycotrophic Bidens maximowicziana and non-mycotrophic Amaranthus retroflexus (referred to by genus hereafter), by growing them either in two-species mixtures or in monocultures. We found that the growth of Flaveria was suppressed by its association with AM fungi regardless of the presence of competing native species, but the degree of suppression was related to the native species with which Flaveria competed. When growing in monocultures, all three species showed a strong preference for NO3−-N over NH4+-N and glycine-N regardless of mycorrhizal status. However, under competition conditions, Flaveria increased 15N recovery in any form of N available (in particular NH4+-15N), depending on neighboring plant identity and AM fungi association, whereas Amaranthus specially tended to decrease NH4+-15N uptake when competing with Flaveria, suggesting a niche complementarity in the utilization of N between two species. Our findings suggested that AM fungi may have the potential to limit the invasion of Flaveria, in the short term, and that interspecific competition plays an important role in partitioning soil N acquisition between plant species. [ABSTRACT FROM AUTHOR]

Elevated atmospheric N deposition has been well documented to enhance fine root production in N-limited temperate forests, but how fine roots respond to N deposition in N-rich tropical and subtropical forests remains poorly understood. The sequential coring and minirhizotron methods were applied to quantify fine root biomass, production, and turnover of a N-rich but P-limited subtropical forest in southern China and to assess the responses of these root variables to a gradient of N additions (control (0), low-N (35), medium-N (70), and high-N (105 kg N ha−1 year−1)) during the first 3 years of experimentation. The high- and medium-N additions significantly reduced fine root diameter by about 30% but increased the specific root length by 20–105%, i.e., fine roots became thinner and longer under the experimental N addition. Both low- and medium-N additions generally stimulated fine root production (10–88%) and turnover (3–40%), whereas high-N suppressed them by 32–70% and 8–54%, respectively, varying with sampling season and estimation method. The stimulatory effects were presumably ascribed to the increased fine root growth for P acquisition, the suppressive effect, to the deleterious damage to the root health and micronutrient availability. Overall, the N effects were more pronounced in the surface (0–10 cm) than in the deeper (10–40 cm) soil layers and for the first-order than the higher-order fine roots. Our results indicate that lower-order absorptive fine roots are responsive to elevated N deposition, and complex responses could emerge due to the interactive influences of the N deposition rate, seasonality, and soil depth. [ABSTRACT FROM AUTHOR]

Aims: Invasive plants often modify soil biota to benefit their own fitness over native species, and create a positive plant-soil feedback (PSF). Rhizosphere effect (RE), the alterations of decomposition processes by living roots and associated rhizodeposits, may act as a mechanism that contributes to the positive PSF via accelerating litter decomposition and subsequent soil nutrient turnover. However, the relative effects attributable to litter quality versus plant composition and edaphic conditions on RE remain unclear. Methods: A reciprocal translocation decomposition experiment was conducted in a screenhouse with root litter from an invasive (Flaveria bidentis) and a native species (Bidens maximowicziana) in two types of soils (one dominated by the invasive species and another by the native species) with four plantings (two monocultures, one mixture with both species, and one without living plants). We examined the performance of invasive and native species responses to different soils (PSF) and quantified the RE on litter decomposition. Results: PSF and RE were dependent on whether focal species grew in the monocultures or mixture, and interspecific competition ameliorated negative PSF of F. bidentis when it competed with a weaker competitor. All RE values associated with B. maximowicziana litter under the monocultures were positive, whereas F. bidentis litter exhibited neutral to negative REs, mainly depending on the soil type examined. The RE values in the invaded soil were significantly greater than those in the native soil under the monocultures. However, mixture planting tended to decrease REs on decomposition, which in turn feedback to host plant by affecting soil N availability and microbial composition. Conclusions: Our study showed that innate differences between the two litters in terms of their decomposability and edaphic conditions are likely to exert a much greater impact in controlling litter decomposition. Importantly, rhizosphere-mediate belowground process has the potential to be an important contributor to plant-interaction outcomes. [ABSTRACT FROM AUTHOR]

Background and Aim: Subtropical soils are generally characterized as deficient in phosphorus (P), calcium (Ca) and magnesium (Mg), but rich in iron (Fe) and aluminum (Al). However, soils developed in phosphate rock are extremely P-rich in subtropical forests, southwestern China. Factors controlling plant stoichiometric traits across variable P sites are still not clear.Methods: We investigated leaf macroelements (C, N, P, K, Ca and Mg), microelements (Mn, Fe, Zn, and Cu), and non-essential elements (Na and Al) and their element:P ratios for 21 woody plant species at both P-rich and P-deficient sites.Results: Plants between the two P type sites were mainly discriminated by Mn, Al, N and their P ratios, and between functional groups by Cu, Fe, Zn and their P ratios. There were higher leaf N, P, K, Ca, Fe and Zn concentrations but lower Mn, Cu and Al at the P-rich sites. Evergreen conifers displayed strict homeostasis while evergreen and deciduous broadleaf were more plastic and had variable ratios across different nutrients.Conclusion: Microelements have strong influences on plant stoichiometry to differentiate geologic-derived P sites in subtropics, and three functional group plants have adopted different stoichiometric strategies under variable nutrient conditions. [ABSTRACT FROM AUTHOR]

Background: Differences in cropping systems and their impacts on plant growth and carbon (C) uptake as well as soil C release pose a major challenge in projecting agroecosystem C balance. Methods: A four-year (2012-2015) field experiment was conducted to examine crop C uptake and soil respiration in two conventional (wheat-cotton and wheat-maize) and two legume-based (wheat-soybean and alfalfa-maize) double-season cropping systems in North China Plain. Results: During the 4 experimental years, crop C uptake was greater in the two conventional systems than the two legume-based systems. However, soil respiration was higher in the two systems with C (i.e. maize) than C crops (i.e. cotton and soybean) planted in summer. As consequences, cropland C balance was positive in the two conventional cropping systems, with greater value in the wheat-maize comparing to wheat-cotton system. However, the two legume-based cropping systems showed negative cropland C balance. Conclusions: Our findings indicate that, although more CO-C is emitted in maize-related cropping systems, the conventional agricultural activities may sequestrate more C in comparison with the legume-based farming in North China Plain due to higher C uptake, and highlight the importance of management strategy in improving agroecosystem C storage. [ABSTRACT FROM AUTHOR]

Aims: The objective of this study was to investigate the effects of the precipitation changes on soil, microbial and root respirations of switchgrass soils, and the relationships between soil respiration and plant growth, soil moisture and temperature. Methods: A mesocosm experiment was conducted with five precipitation treatments over two years in a greenhouse in Nashville, Tennessee. The treatments included ambient precipitation, −50%, −33%, +33% and +50% of ambient precipitation. Soil, microbial, and root respirations were quantified during the growing seasons. Results: Mean soil and root respirations in the +50% treatment were the highest (2.48 and 0.93 μmol CO m s, respectively) among all treatments. Soil microbial respiration contributed more to soil respiration, and had higher precipitation sensitivity mostly than root respiration. Increases in precipitation mostly enhanced microbial respiration while decreases in precipitation reduced both microbial and root respirations. Across precipitation treatments, soil respiration was significantly influenced by soil moisture, soil temperature, and aboveground biomass. Conclusions: Our results showed that microbial respiration was more sensitive to precipitation changes, and precipitation regulated the response of soil respiration to soil temperature. The information generated in this study will be useful for model simulation of soil respiration in switchgrass fields under precipitation changes. [ABSTRACT FROM AUTHOR]

Introduction: Soil heterotrophic respiration ( R , an indicator of soil organic carbon decomposition) is an important carbon efflux of terrestrial ecosystems. However, the dynamics of soil R and its empirical relations with climatic factors have not been well understood. Methods: We incubated soils of three subtropical forests at five temperatures (10, 17, 24, 31, and 38 °C) and five moistures (20, 40, 60, 80, and 100% water holding capacity (WHC)) over 90 days. R was measured throughout the course of the incubation. Three types of models (log-linear, exponential, and power model) were fitted to the measurements and evaluated based on the coefficient of determination ( r ) and Akaike Information Criterion (AIC) of the model. Further regression analysis was used to derive the empirical relations between model parameters and the two climatic factors. Results: Among the three models, the power function model ( R = R t ) performed the best in fitting the descending trend of soil R with incubation time ( r > 0.69 for 26 of 30 models). Both R and k generally increased linearly with soil temperature but varied quadratically with soil moisture in the three forest soils. Conclusions: This study demonstrated that the power function model was much more accurate than the exponential decay model in describing the decomposition dynamics of soil organic carbon (SOC) in mineral soils of subtropical forests. The empirical relations and parameter values derived from this incubation study may be incorporated into process-based ecosystem models to simulate R responses to climate changes. [ABSTRACT FROM AUTHOR]

It is predicted that locust outbreaks will occur more frequently under future climate change scenarios, with consequent effects on ecological goods and services. A field manipulative experiment was conducted to examine the responses of gross ecosystem productivity (GEP), net ecosystem carbon dioxide (CO) exchange (NEE), ecosystem respiration (ER), and soil respiration (SR) to locust outbreaks in a temperate steppe of northern China from 2010 to 2011. Two processes related to locust outbreaks, natural locust feeding and carcass deposition, were mimicked by clipping 80 % of aboveground biomass and adding locust carcasses, respectively. Ecosystem carbon (C) exchange (i.e., GEP, NEE, ER, and SR) was suppressed by locust feeding in 2010, but stimulated by locust carcass deposition in both years (except SR in 2011). Experimental locust outbreaks (i.e., clipping plus locust carcass addition) decreased GEP and NEE in 2010 whereas they increased GEP, NEE, and ER in 2011, leading to neutral changes in GEP, NEE, and SR across the 2 years. The responses of ecosystem C exchange could have been due to the changes in soil ammonium nitrogen, community cover, and aboveground net primary productivity. Our findings of the transient and neutral changes in ecosystem C cycling under locust outbreaks highlight the importance of resistance, resilience, and stability of the temperate steppe in maintaining reliable ecosystem services, and facilitate the projections of ecosystem functioning in response to natural disturbance and climate change. [ABSTRACT FROM AUTHOR]

Aims: Drivers of soil respiration ( R) in rock outcrop ecosystems remain poorly understood. We investigated these drivers in limestone cedar glades, known for their concentrations of endemic plant species and for seasonal hydrologic extremes (xeric and saturated conditions), and compared our findings to those in temperate grasslands and semi-arid ecosystems. Methods: We measured R, soil temperature ( T), volumetric soil water content (SWC), soil organic matter (SOM), soil depth, and vegetation cover monthly over 16 mo and analyzed effects of these variables on R. Results: Seasonally, R primarily tracked T (r = 0.77; P < 0.01), however R was depressed during a summer drought. SOM was highly variable spatially, and incorporating SOM effects into the R model dramatically improved model performance. Both shallow soil and sparse vegetation cover were also associated with lower R. Conclusions: Soil depth, SOM, and vegetation cover were important drivers of R in limestone cedar glades. Seasonal R patterns reflected those for mesic temperate grasslands more than for semi-arid ecosystems, in that R primarily tracked temperature for most of the year. [ABSTRACT FROM AUTHOR]

Terrestrial ecosystems in the southern United States (SUS) have experienced a complex set of changes in climate, atmospheric CO concentration, tropospheric ozone (O), nitrogen (N) deposition, and land-use and land-cover change (LULCC) during the past century. Although each of these factors has received attention for its alterations on ecosystem carbon (C) dynamics, their combined effects and relative contributions are still not well understood. By using the Dynamic Land Ecosystem Model (DLEM) in combination with spatially explicit, long -term historical data series on multiple environmental factors, we examined the century-scale responses of ecosystem C storage and flux to multiple environmental changes in the SUS. The results indicated that multiple environmental changes shifted SUS ecosystems from a C source of 1.20 ± 0.56 Pg (1 Pg = 10 g) during the period 1895 to 1950, to a C sink of 2.00 ± 0.94 Pg during the period 1951 to 2007. Over the entire period spanning 1895-2007, SUS ecosystems were a net C sink of 0.80 ± 0.38 Pg. The C sink was primarily due to an increase in the vegetation C pool, whereas the soil C pool decreased during the study period. The spatiotemporal changes of C storage were caused by changes in multiple environmental factors. Among the five factors examined (climate, LULCC, N deposition, atmospheric CO, and tropospheric O), elevated atmospheric CO concentration was the largest contributor to C sequestration, followed by N deposition. LULCC, climate, and tropospheric O concentration contributed to C losses during the study period. The SUS ecosystem C sink was largely the result of interactive effects among multiple environmental factors, particularly atmospheric N input and atmospheric CO [ABSTRACT FROM AUTHOR]

Temperature sensitivity of soil respiration ( Q 10) is an important parameter in modeling the effects of global warming on ecosystem carbon release. Experimental studies of soil respiration have ubiquitously indicated that Q 10 has high spatial heterogeneity. However, most biogeochemical models still use a constant Q 10 in projecting future climate change and no spatial pattern of Q 10 values at large scales has been derived. In this study, we conducted an inverse modeling analysis to retrieve the spatial pattern of Q 10 in China at 8 km spatial resolution by assimilating data of soil organic carbon into a process-based terrestrial carbon model (CASA model). The results indicate that the optimized Q 10 values are spatially heterogeneous and consistent to the values derived from soil respiration observations. The mean Q 10 values of different soil types range from 1.09 to 2.38, with the highest value in volcanic soil, and the lowest value in cold brown calcic soil. The spatial pattern of Q 10 is related to environmental factors, especially precipitation and top soil organic carbon content. This study demonstrates that inverse modeling is a useful tool in deriving the spatial pattern of Q 10 at large scales, with which being incorporated into biogeochemical models, uncertainty in the projection of future carbon dynamics could be potentially reduced. [ABSTRACT FROM AUTHOR]

The aim of this research is to propose an improved method to partition single species contributions to decomposition in mixed species litters and to detect additive or non-additive responses in litter decomposition. Using simulated data, we demonstrate that additive responses can arise from multiple conditions, including no changes in litter decomposition rates of both species in the mixtures, or an enhanced decomposition of one species and a reduced decomposition of another. Antagonistic responses can be caused by reduced decomposition of only one species, or of both species. Without partitioning of the contributions of single species proposed here, it is difficult to distinguish the different causes of the overall responses. Our analyses provide a better understanding of litter decomposition in mixtures and have significant implications for modeling litter decomposition. [ABSTRACT FROM AUTHOR]

Extracellular glycosidases in soil, produced by microorganisms, act as major agents for decomposing labile soil organic carbon (e.g., cellulose). Soil extracellular glycosidases are significantly affected by nitrogen (N) fertilization but fertilization effects on spatial distributions of soil glycosidases have not been well addressed. Whether the effects of N fertilization vary with bioenergy crop species also remains unclear. Based on a 3-year fertilization experiment in Middle Tennessee, USA, a total of 288 soil samples in topsoil (0–15 cm) were collected from two 15 m2 plots under three fertilization treatments in switchgrass (SG: Panicum virgatum L.) and gamagrass (GG: Tripsacum dactyloides L.) using a spatially explicit design. Four glycosidases, α-glucosidase (AG), β-glucosidase (BG), β-xylosidase (BX), cellobiohydrolase (CBH), and their sum associated with C acquisition (Cacq) were quantified. The three fertilization treatments were no N input (NN), low N input (LN: 84 kg N ha−1 year−1 in urea) and high N input (HN: 168 kg N ha−1 year−1 in urea). The descriptive and geostatistical approaches were used to evaluate their central tendency and spatial heterogeneity. Results showed significant interactive effects of N fertilization and crop type on BX such that LN and HN significantly enhanced BX by 14% and 44% in SG, respectively. The significant effect of crop type was identified and glycosidase activities were 15–39% higher in GG than those in SG except AG. Within-plot variances of glycosidases appeared higher in SG than GG but little differed with N fertilization due to large plot-plot variation. Spatial patterns were generally more evident in LN or HN plots than NN plots for BG in SG and CBH in GG. This study suggested that N fertilization elevated central tendency and spatial heterogeneity of glycosidase activities in surficial soil horizons and these effects however varied with crop and enzyme types. Future studies need to focus on specific enzyme in certain bioenergy cropland soil when N fertilization effect is evaluated. [ABSTRACT FROM AUTHOR]

Extreme precipitation events are predicted to occur more frequently and will have significant influences on terrestrial ecosystem carbon (C) cycling in the future. However, response patterns of soil respiration to precipitation changes remain uncertain in terrestrial ecosystems. A field experiment with seven precipitation treatments (i.e. from −60% to +60% of ambient precipitation to form a drought to wet precipitation gradient) was conducted over three growing seasons (2010-2012) in a semiarid temperate steppe of Northern China. Results showed a nonlinear response pattern of soil respiration along the experimental precipitation gradient, with soil respiration suppressed by decreased precipitation and enhanced by increased precipitation. Over the three growing seasons, soil respiration was reduced more under the three drought treatments (by 45.8, 32.8, and 15.9% under the −60, −40, and −20% treatments, respectively) than stimulated under the three wet treatments (by 8.9, 14.3, and 18.5% under the +20, +40, and +60% treatments, respectively). Our results indicate that soil respiration was more sensitive to decreased than increased precipitation treatments. The nonlinear and asymmetric responses of soil respiration to precipitation changes should be built into ecosystem models to project ecosystem C cycling associated with climate change. [ABSTRACT FROM AUTHOR]

How soil microbes assimilate carbon-C, nitrogen-N, phosphorus-P, and sulfur-S is fundamental for understanding nutrient cycling in terrestrial ecosystems. We compiled a global database of C, N, P, and S concentrations in soils and microbes and developed relationships between them by using a power function model. The C:N:P:S was estimated to be 287:17:1:0.8 for soils, and 42:6:1:0.4 for microbes. We found a convergence of the relationships between elements in soils and in soil microbial biomass across C, N, P, and S. The element concentrations in soil microbial biomass follow a homeostatic regulation curve with soil element concentrations across C, N, P and S, implying a unifying mechanism of microbial assimilating soil elements. This correlation explains the well-constrained C:N:P:S stoichiometry with a slightly larger variation in soils than in microbial biomass. Meanwhile, it is estimated that the minimum requirements of soil elements for soil microbes are 0.8 mmol C Kg−1 dry soil, 0.1 mmol N Kg−1 dry soil, 0.1 mmol P Kg−1 dry soil, and 0.1 mmol S Kg−1 dry soil, respectively. These findings provide a mathematical explanation of element imbalance in soils and soil microbial biomass, and offer insights for incorporating microbial contribution to nutrient cycling into Earth system models. [ABSTRACT FROM AUTHOR]

A letter to the editor is presented in response to the article "Asia on the rise" published in the previous issue.

Aims: Soil comprises diverse carbon (C) pools undergoing various decomposition stages, each characterized by distinct stability and turnover rates. The response of these C pools to warming with the input of plant residues remains unclear.We conducted a 90-day incubation study at 15 °C and 25 °C, introducing 13C-labeled cellulose into soils from old-field (OF), bare-fallow (BF), and bare-fallow plus 815-day pre-incubation (BF+) representing different stages of soil organic matter decomposition.We estimated the priming effects (PE) of cellulose and found that PE were 30.6%, 59.3%, and 63.0% at 15 °C, and 20.8%, 35.3%, and 39.8% at 25 °C for OF, BF, and BF + soils, respectively. Net C balance was higher in BF and BF + soils than in OF soil by 0.6 − 2.8 mg C g−1 SOC at 15 °C and 1.8 − 3.8 mg C g−1 SOC at 25 °C. This indicated both PE and net C balance declined with warming regardless of soil C pool stability, but much greater in soil C pools at a slower decomposition stage.Overall, this study underscores warming can uniformly decrease soil C sequestration potential although the distinct priming effects of the soil C pools at different decomposition stages.Methods: Soil comprises diverse carbon (C) pools undergoing various decomposition stages, each characterized by distinct stability and turnover rates. The response of these C pools to warming with the input of plant residues remains unclear.We conducted a 90-day incubation study at 15 °C and 25 °C, introducing 13C-labeled cellulose into soils from old-field (OF), bare-fallow (BF), and bare-fallow plus 815-day pre-incubation (BF+) representing different stages of soil organic matter decomposition.We estimated the priming effects (PE) of cellulose and found that PE were 30.6%, 59.3%, and 63.0% at 15 °C, and 20.8%, 35.3%, and 39.8% at 25 °C for OF, BF, and BF + soils, respectively. Net C balance was higher in BF and BF + soils than in OF soil by 0.6 − 2.8 mg C g−1 SOC at 15 °C and 1.8 − 3.8 mg C g−1 SOC at 25 °C. This indicated both PE and net C balance declined with warming regardless of soil C pool stability, but much greater in soil C pools at a slower decomposition stage.Overall, this study underscores warming can uniformly decrease soil C sequestration potential although the distinct priming effects of the soil C pools at different decomposition stages.Results: Soil comprises diverse carbon (C) pools undergoing various decomposition stages, each characterized by distinct stability and turnover rates. The response of these C pools to warming with the input of plant residues remains unclear.We conducted a 90-day incubation study at 15 °C and 25 °C, introducing 13C-labeled cellulose into soils from old-field (OF), bare-fallow (BF), and bare-fallow plus 815-day pre-incubation (BF+) representing different stages of soil organic matter decomposition.We estimated the priming effects (PE) of cellulose and found that PE were 30.6%, 59.3%, and 63.0% at 15 °C, and 20.8%, 35.3%, and 39.8% at 25 °C for OF, BF, and BF + soils, respectively. Net C balance was higher in BF and BF + soils than in OF soil by 0.6 − 2.8 mg C g−1 SOC at 15 °C and 1.8 − 3.8 mg C g−1 SOC at 25 °C. This indicated both PE and net C balance declined with warming regardless of soil C pool stability, but much greater in soil C pools at a slower decomposition stage.Overall, this study underscores warming can uniformly decrease soil C sequestration potential although the distinct priming effects of the soil C pools at different decomposition stages.Conclusions: Soil comprises diverse carbon (C) pools undergoing various decomposition stages, each characterized by distinct stability and turnover rates. The response of these C pools to warming with the input of plant residues remains unclear.We conducted a 90-day incubation study at 15 °C and 25 °C, introducing 13C-labeled cellulose into soils from old-field (OF), bare-fallow (BF), and bare-fallow plus 815-day pre-incubation (BF+) representing different stages of soil organic matter decomposition.We estimated the priming effects (PE) of cellulose and found that PE were 30.6%, 59.3%, and 63.0% at 15 °C, and 20.8%, 35.3%, and 39.8% at 25 °C for OF, BF, and BF + soils, respectively. Net C balance was higher in BF and BF + soils than in OF soil by 0.6 − 2.8 mg C g−1 SOC at 15 °C and 1.8 − 3.8 mg C g−1 SOC at 25 °C. This indicated both PE and net C balance declined with warming regardless of soil C pool stability, but much greater in soil C pools at a slower decomposition stage.Overall, this study underscores warming can uniformly decrease soil C sequestration potential although the distinct priming effects of the soil C pools at different decomposition stages. [ABSTRACT FROM AUTHOR]