Abstract: Vegetation near-soil-surface factors can protect topsoil from erosion, however, their contributions to the reduction of soil erosion, especially under natural rainfall events, have not been systematically recognized. This study was performed to quantify the effects of near-soil-surface factors on runoff and sediment under natural rainfall events on grasslands dominated by Bothriochloa ischaemum (Linn.) Keng (BI grassland) and Artemisia gmelinii Thunb. (AG grassland) in two typical watersheds on the Loess Plateau, China in 2018. By successive removal of the plant canopy, litter, biological soil crusts (BSCs) and plant roots, we established five treatments including plant roots, plant roots+BSCs, plant roots+BSCs+litter, intact grassland and bare land in each grassland type. In total, twenty runoff plots (5 m×3 m) with similar slopes and aspects were constructed in the two types of grasslands. Results showed that plant canopy, litter and roots reduced runoff, while BSCs, which swelled in the presence of water, increased runoff. In contrast, all of these factors reduced sediment yield. In addition, the reductions in runoff and sediment yield increased with I30 (maximum 30-min rainfall intensity) for each vegetation near-soil-surface factor except for BSCs. Among these factors, plant canopy had the largest contribution to runoff reduction, accounting for 48.8% and 39.9% in the BI and AG grasslands, respectively. The contributions of these vegetation near-soil-surface factors to sediment yield reduction were similar (21.3%–29.9%) in the two types of grasslands except for BSCs in the AG grassland (10.3%). The total reduction in runoff in the BI grassland (70.8%) was greater than that in the AG grassland (53.1%), while the reduction in sediment yield was almost the same in both grasslands (97.4% and 96.7%). In conclusion, according to the effects of different vegetation near-soil-surface factors on runoff and sediment production, our results may provide more complete insight and scientific basis into the effects of various vegetation related factors in controlling soil erosion.
摘要：The distribution of binding agents (i.e., soil organic carbon (SOC) and glomalin-related soil protein (GRSP)) in soil aggregates was influenced by many factors, such as plant characteristics and soil properties. However, how these factors affect binding agents and soil aggregate stability along a climatic gradient remained unclear. We selected the Robinia pseudoacacia L. forests from semi-arid to semi-humid of the Loess Plateau, China to analyze the plant biomass, soil physical-chemical properties, SOC and GRSP distribution in different sized soil aggregates. We found that from semi-arid to semi-humid forests: (1) the proportion of macro-aggregates (>0.250 mm) significantly increased (P<0.05), whereas those of micro-aggregates (0.250–0.053 mm) and fine materials (<0.053 mm) decreased and soil aggregate stability was increased; (2) the contents of SOC and GRSP in macro-aggregates and micro-aggregates significantly increased, and those in fine materials decreased; (3) the contribution of SOC to soil aggregate stability was greater than those of total GRSP and easily extractable GRSP; (4) soil properties had greater influence on binding agents than plant biomass; and (5) soil aggregate stability was enhanced by increasing the contents of SOC and GRSP in macro-aggregates and soil property was the important part during this process. Climate change from semi-arid to semi-humid forests is important factor for soil structure formation because of its positive effect on soil aggregates.
摘要：The lack of clarity of how natural vegetation restoration influences soil organic carbon (SOC) content and SOC components in soil aggregate fractions limits the understanding of SOC sequestration and turnover in forest ecosystems. The aim of this study was to explore how natural vegetation restoration affects the SOC content and ratio of SOC components in soil macroaggregates (>250 µm), microaggregates (53–250 µm), and silt and clay (<53 µm) fractions in 30-, 60-, 90- and 120-year-old Liaodong oak (Quercus liaotungensis Koidz.) forests, Shaanxi, China in 2015. And the associated effects of biomasses of leaf litter and different sizes of roots (0–0.5, 0.5–1.0, 1.0–2.0 and >2.0 mm diameter) on SOC components were studied too. Results showed that the contents of high activated carbon (HAC), activated carbon (AC) and inert carbon (IC) in the macroaggregates, microaggregates and silt and clay fractions increased with restoration ages. Moreover, IC content in the microaggregates in topsoil (0–20 cm) rapidly increased; peaking in the 90-year-old restored forest, and was 5.74 times higher than AC content. In deep soil (20–80 cm), IC content was 3.58 times that of AC content. Biomasses of 0.5–1.0 mm diameter roots and leaf litter affected the content of aggregate fractions in topsoil, while the biomass of >2.0 mm diameter roots affected the content of aggregate fractions in deep soil. Across the soil profiles, macroaggregates had the highest capacity for HAC sequestration. The effects of restoration ages on soil aggregate fractions and SOC content were less in deep soil than in topsoil. In conclusion, natural vegetation restoration of Liaodong oak forests improved the contents of SOC, especially IC within topsoil and deep soil. The influence of IC on aggregate stability was greater than the other SOC components, and the aggregate stability was significantly affected by the biomasses of litter, 0.5–1.0 mm diameter roots in topsoil and >2.0 mm diameter roots in deep soil. Natural vegetation restoration of Liaodong oak forests promoted SOC sequestration by soil macroaggregates.