Interactions of soil nutrients and microbial communities during root decomposition of gramineous and leguminous forages

Soil microorganisms are involved in the litter decomposition process and are closely related to nutrient cycling in ecosystems, especially carbon (C) and nitrogen (N) cycling. For grassland ecosystems, most grassland biomass is invested in the root system. Therefore, to determine the influence of root decomposition on soil microorganisms in different grassland species, an in-situ root decomposition experiment was conducted with two species (gramineous forage: Bothriochloa ischaemum and leguminous forage: Lespedeza davurica) over three decomposition times (90, 270 and 450 days). Total organic carbon (TOC) and total nitrogen (TN) in the roots of the two species decreased gradually. And L. davurica had higher soil organic carbon (SOC) and soil total nitrogen (STN) in the late stage. Proteobacteria, Chloroflexi and Acidobacteria were the dominant bacteria, and Ascomycota and Basidiomycota were the dominant fungi in the two species. STN is the most important factor driving changes in soil microbial communities. The alpha diversity index of bacteria in both species showed an increasing trend, while in fungi, it decreased rapidly at the early stage and increased slightly at the late stage. Compared with the bacteria in B. ischaemum, L. davurica increased some submetabolic system pathway genes related to carbon cycle metabolism. FUNGuild revealed that saprotrophic fungi on the 90(th) day were significantly lower than those on the 270(th) and 450(th) days. Our results show that leguminous forages have better performance in improving SOC and STN, and microbial characteristics are also affected by species during root decomposition.