In the global change scenario, nitrogen (N) deposition has the potential to affect the soil microbial communities that play critical roles in ecosystem functioning. Although the impacts of N deposition on soil microbial communities have been reasonably well studied, microorganism responses to the N addition combined with the seasonal change have rarely been reported. This study was conducted to evaluate the effects of different levels of N addition (0, 2.5, 5.0, and 7.5 g N·m⁻²·yr⁻¹) on soil microbial communities in different seasons (spring, summer, and autumn) in a boreal forest. Our results showed that the soil physical–chemical properties were found to be changed by N addition and seasonal changes were correlated with microbial community structure. The N addition and seasonal changes significantly affect the diversity and abundance of the microbial community, while their interactions only affect the bacterial abundance and the fungal diversity. In addition, our results also provided clear evidence for specific responses of microorganisms to the different N additions and each season. Our findings suggest that the microbial community response to N deposition could be the seasonal change and will strongly correlate with environmental change.

Understanding the mechanisms controlling forest carbon accumulation is crucial for predicting and mitigating future climate change. Yet, it remains unclear whether the dominance of ectomycorrhizal (EcM) trees influences the carbon accumulation of entire forests. In this study, we analyzed forest inventory data from over 4000 forest plots across Northeast China. We find that EcM tree dominance consistently exerts a positive effect on tree, soil, and forest carbon stocks. Moreover, we observe that these positive effects are more pronounced during unfavorable climate conditions, at lower tree species richness, and during early successional stages. This underscores the potential of increasing the dominance of native EcM tree species not only to enhance carbon stocks but also to bolster resilience against climate change in high-latitude forests. Here we show that forest managers can make informed decisions to optimize carbon accumulation by considering various factors such as mycorrhizal types, climate, successional stages, and species richness.