Divergent responses of soil microbial metabolic limitations to cropland revegetation at erosion and deposition topographies in the hilly-gully region of the northern Loess Plateau, China

AimsCropland revegetation is an effective measure to curb soil erosion on eroding hillslopes and increase farmers' income at depositional check dams. However, how soil microbial metabolic limitation responds to cropland revegetation in erosion and deposition landscapes remains poorly understood, which has substantial implications for carbon (C) retention and nutrient cycling in the eroding environment.MethodsWe sampled 0-2 m soils in cropland and revegetated forest and grassland at upslopes and check dams in the hilly-gully region of the Loess Plateau, China. The activities of soil C-, nitrogen (N)-, and phosphorus (P)-acquiring enzymes were analyzed. The improved enzyme vector model (V-T model) based on balance points was used to quantify microbial metabolic limitations based on ecoenzymatic stoichiometry.ResultsMicroorganisms suffered from no energy (C) limitation, but the relative microbial C limitation was greater in revegetated forest than in cropland. At upslopes, the revegetated forest was primarily limited by P, while the revegetated grassland and cropland were limited by N, which was indicated by the VTN/P limitation values of 4.35, -2.74, and - 1.87, respectively. Microbial P limitation was greater in deep soils of revegetated forest due to the assimilation of P by the root system. At check dams, land-use change had no significant influence on microbial N/P limitations owing to abundant soil C and nutrients and a wet environment.ConclusionConcludingly, cropland revegetation had a weaker influence on microbial metabolic limitation at the lower-lying topography, which compensates for the current understanding of resource restrictions on microorganisms at slopes or flat areas.

Automated summary

This study investigated the microbial activity and resource limitation in soils of cropland, revegetated forest, and grassland in the hilly-gully region of the Loess Plateau, China. It was found that the microbial community in the revegetated forest was relatively carbon-limited compared to cropland, while phosphorus was the primary limiting factor in the revegetated forest at upslopes, and nitrogen was the limiting factor in the revegetated grassland and cropland. However, land-use change had no significant impact on microbial nitrogen/phosphorus limitations in the check dams.