Soil bacteria with distinct diversity and functions mediates the soil nutrients after introducing leguminous shrub in desert ecosystems

Legume plants are pioneer species in desert ecosystem that can be used to reestablish degraded ecosystem functions and soil properties, and reshape underground microbial communities. However, the distribution in soil nutrients and bacterial communities after introducing leguminous shrubs have not been well described. Here, we quantified the variations in soil nutrients and bacterial communities in soil profiles (0–100 cm) across stand ages (5-year, 8-year, 15-year) and severe desertification (SD), and further investigated the bacterial contributions to soil nutrients during stand development. The total phosphorus (TP), total nitrogen (TN) and organic carbon (OC) contents significantly increased, whereas the available nitrogen (AN) and available phosphorus (AP) contents showed a downward trend across stand ages. Bacterial diversity increased after introducing leguminous shrubs. Vertical spatial variation of bacterial communities attenuated during stand development. Bacterial beta-diversity, specific microbial phyla (i.e., Proteobacteria and Firmicutes) and nitrification process were strongly associated with vertical spatial variation in soil nutrients. Combined analyses revealed that leguminous shrubs can ameliorate soil OC, TN and TP with increasing legumes growth time, but could still exhibit no facilitating effect on the improvement of soil available N and P even for legumes aged 15 years. Improving the bioavailability of nutrient elements and microbial function diversity could be targeted for further studies in arid barren sandy.