Addition root exudates increase microbial biomass but decreases diversity and richness.

Plant root exudates play a crucial role in regulating soil microbial communities. However, their diverse composition, low concentrations, and rapid degradability limit our understanding of how specific exudates influence microbial community attributes, such as biomass, diversity, and community structure. This meta-analysis study quantified the effects of exudates addition on soil microbial communities and explored the response mechanisms of different microbial attributes. The results showed that exudates addition significantly promoted microbial biomass but reduced microbial α-diversity, richness, and evenness, while also altering community structure. Natural exudates, with their diverse composition and higher nutrient content, had a stronger effect on promoting microbial biomass, whereas synthetic exudates might lead to the overgrowth of certain bacterial taxa, suppressing microbial community diversity. During the response process, changes in soil available nitrogen were identified as a key predictor for microbial biomass, soil pH as an important predictor for microbial richness and evenness, and the carbon input rate of exudates significantly suppressed α-diversity and altered community structure. Additionally, the C:N ratio of exudates played a critical role in regulating β-diversity and community structure. Overall, this study highlights that beyond the properties of exudates themselves, experimental conditions and changes in soil physicochemical properties are critical factors in microbial community regulation. These findings provide theoretical guidance for further research on the effects of exudates on soil ecosystems.