Revegetation induces asynchronous changes of deep soil carbon and nitrogen stocks in the Loess Plateau of China

Revegetation has been proposed as one of the effective methods for enhancing carbon (C) and nitrogen (N) sequestration. However, the magnitude and direction of soil C and N changes following revegetation remain unclear. To address this issue, we conducted a synthesis analysis based on 6,171 observations of soil organic carbon (SOC) and total nitrogen (STN) from 183 studies in 0–200 cm depth across the Chinese Loess Plateau. Our results revealed revegetation type-specific soil C and N stocks of four soil profiles (0–20, 20–100, 100–200, and 0–200 cm) following five restoration ages (0–5, 6–10, 11–20, 21–30, and > 30 years). In general, significant increases in soil C and N stocks were respectively, observed 21 and 31 years after revegetation for the whole soil layer. In addition, the soil C and N stocks of shrub and grassland were chronologically asynchronous between the deep layer (deeper than 100 cm) and shallow layers, whereas that of forest showed more or less similar temporal dynamics only with slight differences in change rates. Such cross-layer asynchronous were also presented for precipitation and temperature, of which the influences in different soil layers exhibited great nonlinear patterns with different turning points in response to the two climatic factors. Furthermore, compared with natural succession, planted vegetation induced relatively more intensive changes of soil C and N, especially for the forest. Overall, our results revealed revegetation-induced asynchronous changes of soil C and N particularly in the deep layers, and suggest that different patterns of soil C and N stocks should be incorporated into soil C and N modeling and estimation.