Chronic enhanced nitrogen deposition and elevated precipitation jointly benefit soil microbial community in a temperate forest

Global change profoundly impacts carbon and nitrogen (N) cycling processes in terrestrial ecosystems by altering soil microbial communities. However, how enhanced N deposition and elevated precipitation jointly affect soil microbes and the underlying mechanisms remain poorly understood, particularly in forest ecosystems. In a long-term field experiment conducted in a temperate forest in China, we added N and/or water above the forest canopy to investigate their effects on soil microbial communities. Our results showed that N addition led to a decrease in bacterial biomass while increasing fungal biomass, resulting in an alteration of soil microbial community structure. Conversely, water addition did not significantly impact soil microbial communities. However, when N and water were added together, both fungal and bacterial biomass notably increased, leading to alterations in the soil microbial community structure. These results suggested that the effect of N addition could be mediated by elevated precipitation. Precipitation increment amplified the positive impact of N deposition on soil fungi but shifted its impact on bacteria from negative to positive. Additionally, soil bacteria were affected by soil N availability and acidification, as well as litter quality, whereas fungi were regulated by litter quantity and soil organic carbon. This study provides crucial evidence that concurrent enhanced N deposition and elevated precipitation favor soil microbial communities in temperate forests. It highlights the potential of elevated precipitation to alleviate the negative impacts of enhanced N deposition on temperate forest ecosystems, thereby sustaining ecological stability under global change scenarios.