Global climate changes decoupled soil nitrogen mineralization and immobilization

Global climate changefactors (GCFs), including elevated CO2 (eCO2), warming, rainfall, drought, and nitrogen (N) deposition, and their combination have profoundly affected soil N cycling. Organic N mineralization and inorganic N immobilization are two fundamental pathways, whose difference determined soil available N production. However, critical knowledge gaps exist in the effect of GCFs on soil mineralization-immobilization turnover. We conducted a meta-analysis using 662 paired field observations to evaluate the individual and combined effect of GCFs on gross nitrogen mineralization(GM) and immobilization(GI). The results, for the first time, showed that both individual and combined GCFs could increase GM(with overall effect of 0.2434and 0.1840) but decrease GI(with overall effect of -0.1470and -0.1914), potentially increasing the production of available Nin the soil.The decoupling patterns were categorized into: (1) GM increasing and GI unchanging (e.g. eCO2, rainfall, N addition, rainfall+Naddition), (2) GM increasing and GI decreasing (e.g. warming+drought), and(3) GM unchanging and GI decreasing (e.g. warming, eCO2+warming, eCO2+rainfall). In addition, soil GM was influenced by GCFs depending on ecosystems, soil horizons and climatic zones. However, GCFs affected GI regardless of ecosystems, soil horizons and climatic zones, apparently due to the mirror-image responses of GIA and GIN to GCFs. Moreover, soil properties (including pH, total C, total N, and C:N ratio) were the most important factors controlling the response of GM and GI to GCFs, followed by climatic conditions (MAT and MAP) and experimental settings (magnitude and duration). Taken together, these findings suggested an enhanced soil available N production under global climate changes, and soil properties are the first factors to be considered for the evaluation and model-building of soil available N production.