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Plant roots significantly reduce soil detachment by overland flow. However, there have been few studies on how plant growth time and hydrodynamic characteristics affect the erosion‐reducing potential of plant roots. This study cultivated ryegrass (Lolium perenne L.) and alfalfa (Medicago sativa L.) as representative of plants possessing fibrous roots and taproots, respectively, in silty soil from the Loess Plateau, China. Root‐soil composites were collected monthly from March to September 2021 and subjected to flow scouring in a hydraulic flume at a 15° slope using five different flow discharges (0.05, 0.1, 0.15, 0.2 and 0.3 L s−1). The results of the study indicated that root length density, root surface area density and root mass density exhibited a significant increase during the early growth phase, followed by a slight decrease. All parameters of fibrous roots revealed greater values than those of taproots, except for root mass density. The reduction in soil detachment under varying flow shear stresses showed a significant increase during the early phases of growth, followed by a gradual decline. Notably, fibrous roots demonstrated a greater impact on soil detachment than taproots, and this discrepancy fluctuated over time. Moreover, the contributions of fibrous and taproots to reducing soil detachment decreased from 55.81% to 39.66% and from 38.21% to 20.99% with increasing flow shear stress, respectively. It indicated that the erosion‐reducing potential of plant roots was greater when subjected to low‐flow shear stress compared to high‐flow shear stress. This study can provide a scientific basis for understanding the erosion‐reducing potential of plant roots at different growing stages and under varying hydrodynamic characteristics. [ABSTRACT FROM AUTHOR]

Global warming is increasing the frequency and intensity of heat waves and droughts. One important phase in the life cycle of plants is seed germination. To date, the association of the temperature and water potential thresholds of germination with seed traits has not been explored in much detail. Therefore, we set up different temperature gradients (5–35 °C), water potential gradients (−1.2–0 MPa), and temperature × water potential combinations for nine native plants in the Loess Plateau region to clarify the temperature and water combinations suitable for their germination. Meanwhile, we elucidated the temperature and water potential thresholds of the plants and their correlations with the mean seed mass and flatness index by using the thermal time and hydrotime models. According to our findings, the germination rate was positively correlated with the germination percentage and water potential, with the former rising and the latter decreasing as the temperature increased. Using the thermal time and hydrotime models, the seed germination thresholds could be predicted accurately, and the germination thresholds of the studied species varied with an increase in germination percentage. Moreover, temperature altered the impact of water potential on the germination rate. Overall, the base water potential for germination, but not the temperature threshold, was negatively correlated with mean seed mass and was lower for rounder seeds than for longer seeds. This study contributes to improving our understanding of the seed germination characteristics of typical plants and has important implications for the management and vegetation restoration of degraded grasslands. [ABSTRACT FROM AUTHOR]

Vegetation disturbance during infrastructure construction can cause serious ecological problems, especially in fragile environments. The Northern Shaanxi Loess Plateau is an oil industry base in China with a fragile ecosystem. Vegetation restoration on the disturbance area can effectively control soil erosion and ensure the safety of oil pipelines. In the linear disturbance area, surrounding vegetation traits and topography may play an important role in vegetation restoration by influencing propagules and recruitment microsites. This study aimed to reveal the influence of vegetation type and topography on vegetation restoration in the disturbance area along the oil pipeline. The results showed that 89 species were recorded, and they belonged to 30 families and 74 genera. These species were mainly native herbaceous plants, especially perennial herbs. The species number and species diversity index in the disturbance area had a positive relationship with the undisturbed area. The lateral undisturbed vegetation type and species reproductive strategies influenced the vegetation restoration in the disturbance area. The species that produce a large number of seeds or regenerate by rhizome recolonized quickly in the disturbance area. However, the shrubs and arbor species that need seeds for recruitment will take a long time for restoration. The topographic factor had an obvious influence on the vegetation restoration and species diversity in the disturbance areas. On the sunny and steep slopes, vegetation restoration was difficult and slow, and artificial measures were needed to control soil erosion and maintain soil moisture to help seedling recruitment and survival. [ABSTRACT FROM AUTHOR]

Extracellular enzymes are the major mediators of plant residue and organic matter decomposition in soil, frequently associated with microbial metabolic processes and the biochemical cycling of nutrients in soil ecosystems. However, the dynamic trends and driving factors of extracellular enzymes and their stoichiometry during plant residue transformation remain to be further studied. Here, we investigated the dynamics of extracellular enzymes and enzymatic stoichiometry in the "litter-soil" transformation interface soil (TIS) layer, an essential occurrence layer for microbially-mediated C transformation. The results indicated an unbalanced relationship between substrate resource supply and microbial metabolic demand. Microbial metabolism was limited by C (C/N-acquiring enzymes > 1) and P (N/P-acquiring enzymes < 1) throughout the observed stages of plant residue transformation. The initially higher extracellular enzyme activity reflected the availability of the active components (dissolved carbon (DC), nitrogen (DN), microbial biomass carbon (MBC), nitrogen (MBN), and phosphorus (MBP)) in the substrate and the higher intensity of microbial metabolism. With the transformation of plant residues, the active fraction ceased to be the predominant microbial C source, forcing the secretion of C-acquiring enzymes and N-acquiring enzymes to obtain C sources and N nutrients from refractory substrates. Moreover, C/N-acquiring enzymes decreased, while C/P-acquiring enzymes and N/P-acquiring enzymes subsequently increased, which suggested that the microbial demand for N gradually increased and for P relatively decreased. Soil microorganisms can be forced into dormancy or intracellular mineralization due to the lack of substrate resources, so microbial biomass and extracellular enzyme activities decreased significantly compared to initial values. In summary, the results indicated that soil nutrients indirectly contribute to extracellular enzymes and their stoichiometry by affecting microbial activities. Furthermore, extracellular enzymes and their stoichiometry were more sensitive to the response of soil microbial biomass carbon. [ABSTRACT FROM AUTHOR]

Due to the atmospheric nuclear weapon tests carried out, terrestrial environments have been extensively contaminated by global fallout of plutonium (Pu) worldwide. The 249+240Pu inventories in soil profiles from undisturbed and flat forest or grasslands (reference sites) mainly from Europe and Asia are considered as important background for evaluating soil erosion. Thus, we conducted a literature survey over an area extending from 2.6°W to 148.9°E and from 53.2°S to 76.6°N, with the purpose of analyzing the spatial distribution of 239+240Pu inventories and possible controlling factors. The aim of this work was to derive an empirical model of 239+240Pu inventory based on currently available 239+240Pu data, precipitation and latitude. The results show that, in general, the latitudinal distribution of 239+240Pu inventory was consistent with the UNSCEAR reports. However, the 239+240Pu inventories are higher than the UNSCEAR data, especially in the Northern Hemisphere. In addition, close relationships (at the 0.01 significance level) were identified between 239+240Pu inventories and annual precipitation and latitude. An empirical formula was therefore developed to estimate 239+240Pu inventories in soils based on latitude and precipitation data. However, future research may require more data of measured 239+240Pu inventories in soil profiles that can be used to compare, validate and improve upon the accuracy of the inferred empirical equation. [ABSTRACT FROM AUTHOR]

Temporal and spatial variations in reference evapotranspiration (ET0) and aridity index (AI) can be used as important indexes for understanding climate change and its effects on ecosystem stability. Thus, in this work, we comprehensively investigated 71 meteorological stations in Northeast China from 1965 to 2017 to analyze the spatial-temporal variation and trend of ET0 and AI using the nonparametric Mann–Kendall test, the linear regression, and the Morlet wavelet methods. The results elucidated that ET0 for Northeast China as a whole exhibited a decrease at a rate of −1.97 mm/yr, AI declined at a rate of −0.01/yr during 1965–2017, and approximately 94% stations showed a decrease trend. Spatially, the high values of AI and ET0 were primarily at the western part of the study area except for the Heilongjiang province, and the stations showing low values were mainly distributed in the central and eastern part. The decreasing trends for AI were more obvious in the eastern part compared with the western part over the study region. The abrupt changes in AI occurred in 2005 and 2007, whereas only one abrupt change for ET0 occurred in 1995. For annual ET0, there were periods of 3, 7, 11, and 15 yr, and there existed periods of 1, 7, 11, and 13 yr for annual AI. The correlation coefficients implied wind speed and precipitation were the dominant meteorological factors resulting in the ET0 and AI decrease, respectively. Additionally, the change of the Indian summer monsoon index (ISMI) may also contribute to the weakened AI in the study area. Nevertheless, further investigation is still required to clarify the mechanisms for AI and ET0 variations in the future. [ABSTRACT FROM AUTHOR]

Globally, biological soil crusts (BSCs) are crucial ecosystem components that perform essential functions important to ecosystem stability. However, the potential mechanisms of BSC's effect on vascular plant recruitment and establishment are largely unknown. Furthermore, few studies have considered BSC‐vascular plant analyses in conjunction with BSC microenvironments, seed traits, and plant life stages simultaneously. Thus, we chose six typical plants with different seed traits on the Loess Plateau and conducted a growth chamber experiment to evaluate the effects of BSC types, disturbance, seeding positions, and moisture on seed germination, survival, and seedling growth. We also explored the effects of BSC presence and disturbance on seedling emergence through field investigation. The results indicated that the main effects of the four factors, BSC type, disturbance, seeding location, and moisture, and their two‐ and three‐dimensional interactions had significant effects on the performance of most of the studied species. Disturbance and wetting treatments with shorter watering intervals promoted the performance of most plants, and moisture could modify the effect of BSCs on plants. The effect of BSCs on plant performance was related to seed traits and plant life stage and the presence of the BSC promotes the growth of the plants when it reaches the survival stage. In field observations, we found that the number of seedling species was lower on BSCs compared to bare lands and that the number of species on broken crusts was greater than on intact crusts; while seedling density on bare land was significantly higher than it in BSC patches. [ABSTRACT FROM AUTHOR]

• Estimate the slope stability based on the root reinforcement at different soil depths. • The sum of the shear strength (S r) induced by reinforcement of all < 2 mm roots was considered in Wu-Waldron model. • Analyse the sensitivity of Wu-Waldron model based on series of root tensile characteristics and distributions. • The slope safety factors were calculated by Wu and Waldron model (W & W model) and the infinite slope stability theory. Root reinforcement is considered an important factor contributing to vegetated hillslope stability. The study aims to extend the understanding of spatial variance in the distributions of roots and mechanical characteristics of Artemisia sacrorum (Artemisia gmelinii Web.) regarding root reinforcement after returning cropland to forestland and grassland on the Loess Plateau of China. The Wu and Waldron model (WW model) and infinite slope method were adopted to estimate the sensitivity of root reinforcement to the mechanical characteristics and the distributions of roots. The results demonstrated that 1) over 80% of root parameters were found in the top 0.3 m soil layer, in which the proportions of the densities of root length (RLD), root surface area (RSAD) and root volume (RVD) were 81.7%, 89.9% and 92.7%, respectively. The root parameters declined with increasing soil depth. 2) The tensile characteristics (tensile strength and force) were significantly correlated with the root diameters as power functions. There was a significant difference in tensile strength between the 0 ~ 0.7 mm and other diameter classes, while there was no significant difference amongst the five gauge lengths. 3) The slope safety factor (F s) of Artemisia sacrorum was always larger than 1, both in different soil depths (0.1 m, 0.2 m and 0.3 m) and at slopes < 45° Artemisia sacrorum could mainly stabilise the slope in the silt loam area of the Loess Plateau of China. These conclusions have a theoretical and practical significance for the slope stability, surface landslides and other geological hazards in arid environments. [ABSTRACT FROM AUTHOR]

Soil extracellular enzyme stoichiometry (EES) reflects the biogeochemical balance between microbial metabolic requirements and environmental nutrient availability. Recent research suggests that EES well effect on soil microbial metabolic limitations (SMMLs), however, few field studies have explicitly tested this based on a herbaceous successional chronosequence. We used the EES models to identify the response of SMMLs, and investigated the potential implications of microbial nutritional limitations across the time series (herbaceous succession) and space (transformation interface soil [TIS] and underlying topsoil [UTS] layer) in the grassland restoration series. We show that soil microorganisms were generally limited by C, both in the TIS and UTS. Microbial C-limitation exhibited a unimodal direction, peaking in intermediate successional stages, however, P-limitation presented the opposite trend. During herbaceous succession, microbial P-limitation was more substantial than that in N-limitation. SMMLs gradually transferred from P- to N- and back to P-limitation at later successional stages in the TIS layer. Furthermore, we demonstrate that biotic factors, soil basic index, and soil nutrients explained 92.2 % of the variations in microbial C-limitation and 84.4 % of the variations in microbial P-limitation. Multi–interaction factors exhibited the most significant relative influences of 65.11 % (TIS) and 43 % (UTS) on the SMMLs. Microbial C-limitation was induced by the imbalance between C supply and microbial C demand, whereas the changes in microbial P-limitation were due to the changes in the competition for P between plants and microorganisms. Overall, our findings provide support for microbial C- and P-limitation in the process of herbaceous succession during the restoration. We also highlight the possibility of additive effects on soil SMMLs via interactions of vegetation composition, soil properties, and microbial nutritional demands, which might constrain soil microbial metabolism requirements despite greater living root and litter resource inputs. [Display omitted] • Soil microorganisms were generally limited by C and P during the herbaceous succession. • In the TIS layer, SMMLs gradually transferred from P- to N- and back to P-limitation. • Multi–interaction factors exhibited the most significant relative influences of 65.11 % (TIS) and 43 % (UTS) on the SMMLs. • Microbial C-limitation was induced by the imbalance between plant residure C supply and microbial C demand. • The changes in microbial P-limitation were due to the changes in the competition for P between plants and microorganisms. [ABSTRACT FROM AUTHOR]

• Background value of Pu atom ratio and activity in the China Seas is established. • Global fallout and PPG are the major source of Pu in the China Seas. • Surface Pu activity in sediments in estuary area is lower than that in shelf region. • Pu in seawater in nearshore area is scavenged more efficiently than in open sea. • Analytical method for Pu analysis in small-volume seawater is highly required. Due to atmospheric nuclear weapon tests carried out by various countries and the ground-level test series conducted at Marshall Islands by the US, marine environments have been extensively contaminated by plutonium over the Western Pacific marginal seas, especially in the China Seas. The released plutonium isotopes can serve as geochemical tracers for various physical and biogeochemical ocean processes. In this critical review, the source term, temporal-spatial distribution and geochemical behavior of plutonium isotopes in seawater and sediments in the China Seas are summarized and discussed, and then they are compared to those in the neighboring seas. A database of plutonium activity concentrations, isotope ratio, and inventories in marine environments in the China Seas is established. We concluded that global fallout and the Pacific Proving Grounds were still the major source of plutonium in the China Seas. The spatial distributions of plutonium in the China Seas indicated surface plutonium activity concentration in sediments in estuary area is lower than that in shelf region, and we thus clarified that plutonium in seawater in nearshore area is scavenged more efficiently than in open sea. Finally, future research needs for plutonium in marine environments are discussed. [ABSTRACT FROM AUTHOR]

Patchiness of grassland results in important effects on ecohydrological processes in arid and semiarid areas; however, the influences on subsurface water flow and soil water distribution remain poorly understood, particularly during vegetation succession on slopes. This study examined these effects by comparing the water flow behaviors and preferential infiltration between vegetation patches (VP) and interspace patches (IP) in three sites at different states of vegetation succession (grass, subshrub and shrub) in abandoned farmland of the Loess Plateau, China. Dye tracer infiltration showed that patchiness of vegetation increased spatial variations of soil water and preferential infiltration by increasing the densities of fine root length and fine root volume in the soil profile. Moreover, the more abundant and intricate roots following a lateral direction beneath VP likely contributed to lateral flow and infiltration variability. However, differences between VP and IP were not significant because considerable living fine roots and decayed roots of IP also provided preferential flow pathways. Our finding indicated that IP could compete with VP for access to soil water resources, which potentially increased hillslope-scale infiltration and reduced surface runoff and erosion risk. Under the different states of vegetation succession, subshrub patches showed significantly greater preferential infiltration volume (28.53 mm) and contribution of preferential infiltration to total infiltration (60.58%) than grass and shrub patches. Vegetation patch size made positive effects on improving preferential flow and water movement. Greater preferential flow in subshrub patches played a positive role in soil water storage and replenishment. Therefore, natural restoration of a slope area with small heterogeneity in preferential flow can be successfully applied in the Loess Plateau, particularly during the subshrub succession state. Unlabelled Image • Vegetation patchiness affects soil properties and root systems. • Vegetation patch increases preferential infiltration but not significantly. • Subshurb exhibits the higher preferential flow infiltration than grass and shrub. • Subsurface water flow is controlled by fine roots and vegetation patch size. [ABSTRACT FROM AUTHOR]

[Display omitted] • Strong microbial-substrate interactions exist in transformation interface soil layers. • Microbial metabolism was limited by C and P during litter decomposition. • Microbial non-homeostatic behavior corresponded to the transition stage. • The effect of microbial factors on enzyme stoichiometry was more stable. The relationships between soil eco-enzymatic stoichiometry and substrate stoichiometry could be used to explain nutrient cycling processes regulated by microbial biomass stoichiometry. But what are the relationships between the stoichiometry of resources, microorganisms, and enzymes? We do not have a clear understanding yet, particularly in the different stages of litter decomposition. By analyzing the response of extracellular enzymatic stoichiometry to the imbalance between microbial and substrate stoichiometry, we explore the microbial-mediated litter transformation and microbial adaptation mechanisms in the transformation interface soil (TIS) layer. The results showed that soil microbial metabolism was limited by C and P during decomposition, peaking in the transition (middle) stage and then gradually decreasing. According to the judgment of microbial homeostasis (effect of substrate stoichiometry on microbial biomass stoichiometry), the microbial communities shift from homeostatic in the early stage to non-homeostatic in the middle stage and then return to homeostasis in the later stage. During the litter decomposition, the non-homeostatic period corresponded to the transition stage. That means severe microbial metabolic limitation is a potential determinant of microbial homeostasis. Soil microorganisms adapt and alleviate microbial metabolic limitations by adjusting extracellular enzyme activity and microbial non-homeostatic behavior when the available resources fail to satisfy microbial requirements. [ABSTRACT FROM AUTHOR]

• Artificial forests had better soil C and N sequestrations than restored grasslands. • Artificial forests and grassland had a similar ability to improve soil aggregates. • N-fixing species played a crucial role in affecting on soil C and N sequestrations. Vegetation restoration is an important factor affecting soil carbon (C) and nitrogen (N) sequestration. However, the effects of the type of vegetation restoration on soil C and N sequestration varies owing to different environmental conditions. Therefore, additional studies should explore the effects of vegetation restoration type on soil C and N sequestration, especially between natural restoration and artificial afforestation. This study explored the differences in improving soil C and N sequestration between artificial forests (AF) and natural grasslands (NG) that had been converted from sloping cropland over 20 years since the implementation of GGP (Grain for Green Program) on the Central Loess Plateau, China. The results showed that NG and AF significantly increased the 0–20 cm soil organic carbon (SOC) content but had a minimal impact on the 20–100 cm SOC content after 20 years of vegetation restoration. In addition, the two vegetation restoration types significantly increased the 0–60 cm soil total nitrogen (STN) content, but they both had no significant effects on the 60–100 cm soil layer. Moreover, the C and N sequestration capacities of AF were higher than those of NG due to the AF had higher plant biomass and lower plant biomass C:N ratios compared to NG. The AF and NG both significantly increased the soil aggregate structure and stability following cropland conversions. Apart from soil aggregates playing a crucial role in affecting soil C and N sequestration, plant biomass and its C:N ratios also had the most substantial effects. The results suggested that soil aggregate stability and the quantity and quality of input organic matter have strongly influenced soil C and N sequestration post-restoration; moreover, N fixing species is more conducive to soil C and N sequestration and the artificial forests had higher C and N sequestration capacities than natural grasslands in the Loess Plateau, with a mean annual precipitation of 505 mm. [ABSTRACT FROM AUTHOR]