Effects of Nitrogen Addition and Precipitation Reduction on Microbial and Soil Nutrient Imbalances in a Temperate Forest Ecosystem

Global climate change, characterized by nitrogen (N) deposition and precipitation reduction, can disrupt soil microbial stoichiometry and soil nutrient availability, subsequently affecting soil nutrient cycles. However, the effects of N deposition and precipitation reduction on microbial stoichiometry and the soil nutrient status in temperate forests remain poorly understood. This study addresses this gap through a 10-year field trial conducted in a Korean pine mixed forest in northeastern China where three treatments were applied: precipitation reduction (PREC), nitrogen addition (N50), and a combination of nitrogen addition with precipitation reduction (PREC-N50). The results showed that N50 and PREC significantly increased carbon-to-phosphorus (C/P) and nitrogen-to-phosphorus (N/P) imbalances, thereby exacerbating microbial P limitation, while PREC-N50 did not alter the nutrient imbalances. PREC decreased soil water availability, impairing microbial nutrient acquisition. Both N50 and PREC influenced soil enzyme stoichiometry, leading to increasing the ACP production. The results of redundancy analysis indicated that microbial nutrient status, enzymatic activity, and composition contributed to the variations in nutrient imbalances, suggesting the adaption of microorganisms to P limitation. These results highlight that N addition and precipitation reduction enhanced microbial P limitation, boosting the shifts of microbial elemental composition, enzyme production, and community composition, and subsequently impacting on forest nutrient cycles.