The coupling interaction of soil water and organic carbon storage in the long vegetation restoration on the Loess Plateau

Secondary succession can recover the properties of degraded soil. The moisture stored in different soil layers is recognized as an important driver of the productivity and sustainability of semi-arid terrestrial ecosystems, and land-use change has a significant effect on the global carbon (C) cycle through changing soil C accumulation rates. To evaluate the response of soil water storage (SWS) and soil organic carbon storage (SOCS) to long-term natural vegetation succession (∼150 a) and the coupling interaction between them, we examined the soil moisture and soil organic carbon content in the land for different restoration ages in the Ziwuling Forest region located in the central part of the Loess Plateau, China. Our results showed that the SWS decreased and the SOCS increased with long-term natural vegetation restoration. The SOCS decreased along with the increase in the soil depth, and it was highest in the topsoil (0-20 cm). In addition, the soil depth at which the SWS intensely varied and at which the SOCS tended to be stable moved downward and upward, respectively, with the vegetation succession. Furthermore, the correlation between SWS and SOCS was significant (P < 0.05) in the long-term restoration and gradually weakened with the increase in the soil depth and the vegetation restoration stages. Clay, silt, sand, total porosity (TP), inactive porosity (IP), aeration porosity (AP) and capillary porosity (CP) were important factors that influenced the coupling interaction of SWS and SOCS at the grass restoration stages (<50 a), and BD influenced this interaction in the shrub and early forest restoration stages (<130 a). The effect of soil physical factors on the interaction of SWS and SOCS gradually weakened during the vegetation restoration succession. These results are expected to help improve the understanding of the response of deep soil water and soil organic carbon to long-term natural vegetation restoration and to provide insights into the coupling interaction between soil water and soil organic carbon influenced by vegetation.