Global climate changes decoupled soil nitrogen mineralization and immobilization

Abstract

Global change factors (GCFs), including elevated CO₂ (eCO₂), warming, increased precipitation (eP), drought, and nitrogen (N) deposition, and their combination have profoundly affected soil N cycling. Despite extensive research, critical gaps remain in understanding GCF effects on soil N mineralization-immobilization turnover (MIT), particularly the individual and interactive effects of GCFs on gross mineralization (GM), immobilization (GI), ammonium immobilization (GIA), and nitrate immobilization (GIN) rates. We conducted a meta-analysis using 631 paired field observations to evaluate the responses of GM, GI, GIA, and GIN to individual and combined GCFs. The results showed that among the examined individual and combined GCFs, 75 % had positive effects on GM, 12.5 % were neutral, and 12.5 % were negative. In contrast, none of the examined GCFs had positive impact on GI, with 50 % showing no effect, and 50 % displaying negative effect. The overall effect of individual GCFs on GM was significantly positive (effect size: 0.312), while their effect on GI was negative (−0.211). Combined GCFs had a significantly positive effect on GM (0.224) but negative effect on GI (−0.756). These findings demonstrate, for the first time, that GCFs may widen the difference between GM and GI, potentially increasing soil available N production. Furthermore, the responses of GI to GCFs showed less sensitivity than that of GM to variations in ecosystems, soil horizons, and climatic zones, likely due to the opposite responses of GIA and GIN to GCFs. Soil properties (e.g., pH and total C) emerged as the primary drivers of GM and GI responses to GCFs, and GCFs duration was also underscored to improve the prediction of soil N cycling under concurrent GCFs. By addressing the research gap in soil N MIT dynamics, our findings enhance the understanding of soil N availability and its implications for ecosystem functioning under future climates.