No abstract

The Grain-for-Green project is an important ecological restoration measure to address the degradation of alpine ecosystems in China, which has an important impact on the ecological stoichiometry of soil carbon (C), nitrogen (N), phosphorus (P) and potassium (K). However, soil stoichiometry changes under different vegetation restoration patterns and at different soil depths remain poorly understood in the alpine region of the Loess Plateau. To clarify these soil stoichiometry changes, a 0–60 cm soil profile was sampled from two typical vegetation restoration patterns: grassland (GL) and forestland (FL), including Picea crassifolia (PC), Larix principis-rupprechtii (LR), Populus cathayana (PR) and Betula platyphylla (BP). The control was a wheat field (WF). In all soil layers, the soil organic carbon (SOC), total nitrogen (TN), soil available nitrogen and potassium (AN and AK, respectively) and C:P, C:K, N:P and N:K ratios of FL were higher than those of GL and WF. The TN content and N:P and N:K ratios of GL were higher than those of WF in each soil layer. Additionally, the soil nutrients (except TK) of all vegetation types and stoichiometry of PR and GL (except the N:P ratio of GL) were greater at 0–20 cm than at 20–60 cm. Moreover, the SOC and TN showed the strongest correlation with the soil stoichiometry (except P:K ratio); thus, C and N had the greatest effect on the soil stoichiometry. Furthermore, soil fertility was limited by N. Our results indicated that different vegetation restoration patterns and soil depths had significant effects on the soil nutrients and stoichiometry in the alpine region of the Loess Plateau. The recovery of farmland to forestland promoted better improvements of soil nutrients, and PR had the most significant positive effect on soil surface nutrients.

Understanding the temporal stability of spatial patterns of soil moisture (SMSP) is essential for predicting and modelling soil moisture; however, there is a relative lack of existing research on the effects of long-term vegetation restoration on the temporal stability of soil moisture. In this study, the temporal stability of soil moisture in the catchment at different stages of vegetation restoration (10 years (RF10), 20 years (RF20) and 40 years (RF40) of farmland rehabilitation) and the associated influencing factors were investigated. The results show that within the RF10 catchment, water deficits occurred during the growing season and that long-term revegetation improved soil moisture in the catchment and increased the water surplus. The overall spatial pattern of soil moisture was consistent across the three catchments. Decreases in soil moisture stability indicators (MRD and ITS) and increases in Spearman’s rank correlation coefficients for soil moisture suggest that revegetation has enhanced the stability of the spatial pattern of soil moisture in the catchment. In addition, the R2 fit of moisture at representative sample sites to the mean moisture in the catchment increased; fluctuations in the spatial pattern of soil moisture were mainly influenced by plant indicators such as fine root biomass (FRB), shrub grass biomass (SGB) and leaf area index (LAI) in the first and middle stages of revegetation, while the temporal stability of soil moisture gradually became more dependent on soil indicators such as Clay and SOC in the middle and late stages of revegetation.