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 90th day were significantly lower than those on the 270th and 450th 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.
Litter decomposition promotes soil carbon and nitrogen cycling and is driven by litter quality, the soil environment and enzyme activities. The relative importance of these factors may change during the litter decomposition, however, very few studies have emphasized the temporal dynamics of these factors across plantation ecosystem, which limits our understanding of litter decomposition. To evaluate the temporal dynamic of above-mentioned litter decomposition drivers, we collected leaf and fine root litters from four different years of restoration of Robinia pseudoacacia on the Loess plateau of China and placed them on soil from the corresponding sites to incubate for 210 days. We constructed successive litter decomposition stages according to litter mass-loss interval, and we also used partial least squares path modelling (PLSPM) to evaluate the relative importance of these drivers. Our results showed that the C and N losses in leaf litter were significantly higher than those in root litter regardless of stand age. Leaf litter C and N losses increased with restoration duration, while root litter C and N showed an opposing trend with restoration duration, with the lowest levels of losses occurring at older stand ages. The initial litter quality, litter quality and the soil environment regulated leaf and root litter C loss, and enzyme activity also determined root C loss. Litter quality, the soil environment and enzyme activity influence leaf litter N loss, while root N loss was controlled by initial litter quality and the soil environment. Overall, enzyme activities had a relatively weak influence on litter C and N losses, and they impacted litter C and N losses only during the early stages. Therefore, our results revealed substantial differences in different restoration durations and litter types at the different decomposition stages, which has important significance for understanding carbon and nitrogen cycling on the Loess Plateau of China.
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