Shifts in fungal communities drive soil profile nutrient cycling during grassland restoration.

Abstract

Soil microbial diversity and community life strategies are crucial for nutrient cycling during vegetation restoration. Although the changes in topsoil microbial communities during restoration have been extensively studied, the structure, life strategies, and function of microbial communities in the subsoil remain poorly understood, especially regarding their role in nutrient cycling during vegetation restoration. In this study, we conducted a comprehensive investigation of the changes in the soil microbial community, assembly process, life strategies, and nutrient cycling functional genes in soil profiles (0-100 cm) across a 36 year chronosequence (5, 15, 28, and 36 years) of fenced grassland and one grazing grassland on the Loess Plateau of China. Our results revealed that soil organic carbon increased by 76.0% in topsoil and 91.6% in subsoil after 36 years of restoration. The bacterial communities were influenced primarily by soil depth, while the fungal communities were highly sensitive to the years of restoration. Microbes in the subsoil recovered faster, and the microbial community structure and functional genes in the soil profiles gradually became more consistent following restoration. In addition, we observed a transition in microbial life history strategies from a persistent K-strategy to a rapid r-strategy during restoration. Notably, the fungal community assembly process played an important role in changes in nutrient cycling genes, which were accompanied by increased carbon fixation and nitrogen mineralization function. Overall, our findings provide several novel insights into the impact of changes in the fungal community on soil nutrient cycling in the soil profile during vegetation restoration.IMPORTANCEOur study revealed that microbes in the subsoil recovered faster than those in the topsoil, which contributed to the reduction in differences in microbial community structure and the distribution of functional genes throughout the soil profile during the restoration process. Importantly, the assembly of fungal communities plays a pivotal role in driving changes in nutrient cycling genes, such as increased carbon fixation and nitrogen mineralization, alongside a reduction in carbon degradation gene abundance. These alterations increase soil organic carbon and nutrient availability during restoration. Our results increase the understanding of the critical role of fungal communities in soil nutrient cycling genes, which facilitate nutrient accumulation in soil profiles during grassland restoration. This insight can guide the development of strategies for manipulating fungal communities to increase soil nutrients in grasslands.