Disentangling the formation and evolvement mechanism of plants-induced dried soil layers on China's Loess Plateau

The extent of the effect of China's Loess Plateau on global climate change partially depends on the achievements of the Grain for Green Program (GFGP). This region is prone to drought problems, especially the widespread creation of dried soil layer (DSL), which is intensified by the revegetation from GFGP initiatives. A DSL is the result of soil desiccation in deep soil profiles. The occurrence and expansion of DSLs are strengthened by the high risk of the Loess Plateau to climate change. On the basis of the 14-year data of soil water content (SWC) of four revegetation types on a loessial slope, we investigated the evolution processes and recovery possibility of DSL. Results showed that both variation trends and abrupt changes in the SWC time series were distinctly affected by revegetation. The 40 cm thickness of the DSL was triggered when Medicago sativa and Caragana korshinskii grew for 2 and 4 years, respectively. The downward extension depth of DSL reached 580 cm under the two plants above within 7 and 8 years of planting. However, the results suggested the possibility of DSL disappearance as shown by the formation depth dynamics of DSL, the fluctuation of DSL-SWC, and the phenomenon of sandwiched DSL. During deep moisture recharge and DSL recovery, although the SWC sensitivity to textural variation was present in the vertical profile, the effects of soil texture on SWC were decreased. Wet climate was linked to both DSL thinning and thickening. Thus, the effect of wet climate is bidirectional for DSL development, thereby highlighting the important role of revegetation. The results of this work enhance our understanding of DSL and may help alleviate the risk of drought in the Loess Plateau.