Soil moisture is an important factor that affects terrestrial vegetation ecosystems and biological growth and development, and water deficit is one of the major environmental factors threatening vegetation restoration in the Loess Plateau. To determine the change in the soil water deficit characteristics from farmland to forestland on the Loess Plateau, in this study, we measured the soil water storage and deficit in abandoned grassland, shrubland, pioneer forestland and climax forestland along with vegetation succession. The results showed that the soil water content and the soil water storage with natural vegetation recovery from the abandoned grassland to shrubland and forestland showed a gradual declining trend, while on the contrary, the soil water deficit was increasing during succession, it was more severe in the deep soil than in the shallow soil layers, and the soil water deficit in July and September of the rainy season as well as that the vigorous growing period of plants was more serious than that in May and November, which are in the non-rainy season of the Chinese Loess Plateau. The vegetation types, soil texture and soil depth were the key factors affecting the soil water deficiency status in the process of vegetation succession. The results could have great potential in the sustainable development of forestry and provide a theoretical basis for effective water management and reasonable vegetation restoration in arid and semiarid loess regions.

Vegetation restoration alters soil biotic and abiotic factors. Plants have evolved multiple strategies to adapt to nutrient limitation by reshaping and recruiting nutrient cycling-associated microbial communities in the rhizosphere. However, our understanding of the co-occurrence patterns of rhizosphere microbial communities and their role in soil multinutrient cycling during vegetation restoration remains limited. The present study explored the co-occurrence patterns of rhizosphere microbial communities along a chronosequence (15–45 years old) in Robinia pseudoacacia plantations in China’s Loess Plateau region, the associations between core microbiota and multinutrient cycling under spatiotemporal changes. Our results indicate that soil multifunctionality influences microbial co-occurrence patterns in the R. pseudoacacia rhizosphere, resulting in a more stable bacterial network than fungal network, forest age was a major driver of modularized distribution of nodes in bacterial and fungal networks, and forest age-sensitive microbes were taxonomically diverse at the phylum level. Meanwhile, we found that core microbiota play essential role in rhizosphere soil multinutrient cycling under R. pseudoacacia afforestation.

Abstract : To address global warming, the carbon sequestration capacity by net primary productivity (NPP) in vegetation on the Loess Plateau (LP) is particularly important as it allows us to adjust the vegetation restoration strategies in response to global changes. However, the spatial correlation of NPP and its impact on vegetation restoration remains unclear. MOD17A3 remote sensing products analyzed the temporal and spatial changes in NPP on the LP over the last two decades (2000–2020). The resulting spatial autocorrelation indices identified cold and hot spots in the spatial clustering patterns. Finally, the effects of climate change and human activities on the anomalous clustering of NPP were assessed using correlation analysis and multi-temporal land use land cover (LULC) data. The results indicate (ⅰ) From 2000 to 2020, the NPP of the LP increased significantly by 6.88   gC m - 2 yr - 1 , and the proportion of revegetated land area > 400   gC m - 2 yr - 1 increased from 4 % (2000) to 37 % (2020). (ⅱ) The vegetation NPP on the LP had a strong positive global spatial autocorrelation (p < 0.01). The hot and cold regions had obvious polarization, in which the cold spots were clustered in the northwest, and the hot spots were distributed in the south and east. The spatial clustering patterns were dominated by high-high (HH) and low-low (LL) clusters. Abnormal patterns mainly existed in the transition areas between HH and LL clusters and insignificant regions, which were jointly affected by human activities and climate change. (ⅲ) Precipitation was the dominant climatic factor (86.31 %) affecting the variation of NPP on the LP, with the annual minimum precipitation showing a synergistic relationship with the interannual variability in NPP and the maximum precipitations greatly influenced the variation in local spatial anomaly patterns. Therefore, climatic extremes affect vegetation. Our research improves our understanding of the driving mechanisms involved in the regional carbon cycle and provides a reference for green ecological management and high-quality development in the LP. Keywords: Net primary productivity, Spatial autocorrelation, Climate change, Human activities, Land use land cover, Loess Plateau

Secondary forest restoration can alter terrestrial ecosystem processes and potentially impact subsurface carbon dynamics. However, the effects of long-term forest restoration on the soil microbial metabolic activity remain unclear. So, the aim of this study was to explore the response of soil microbial metabolism to forest restoration. Among them, the soil basal respiration (BR), microbial quotient ( qMB), and metabolic quotient ( qCO 2) were studied. This study investigated a natural vegetation restoration sequence approximately ~160 years after farmland abandonment on the central Loess Plateau, China, corresponding to five vegetation restoration stages including farmland, grassland, shrubland, pioneer forests, and climax forests. The results showed that BR and qCO 2 were increased following forest restoration, whereas qMB showed the opposite trend. Forest restoration also increased the activities of β-1,4-glucosidase and β-D-cellobiosidase. Restoration age, litter traits such as nitrogen, cellulose and lignin decomposition rates, dissolved organic carbon contents, fungi and bacteria composition were also important indicators affecting microbial metabolic activities. Long-term forest restoration can change soil microbial community structure, reduce carbon mineralization efficiency, improve soil microbial carbon utilization efficiency, and promote soil organic carbon accumulation.