矿化(土壤科学)
硝化作用
土壤水分
环境化学
化学
生态系统
土壤碳
氮气循环
自行车
环境科学
氮气
土壤有机质
农学
土壤科学
生态学
生物
林业
有机化学
地理
作者
Yi Cheng,Jing Wang,Jinyang Wang,Shenqiang Wang,Scott X. Chang,Zucong Cai,Jinbo Zhang,Shuli Niu,Shuijin Hu
标识
DOI:10.1016/j.earscirev.2019.103033
摘要
Reactive nitrogen (N) input can profoundly alter soil N transformations and long-term productivity of forest ecosystems. However, critical knowledge gaps exist in our understanding of N deposition effects on internal soil N cycling in forest ecosystems. It is well established that N addition enhances soil N availability based on traditional net mineralization rate assays. Yet, experimental additions of inorganic N to soils broadly show a suppression of microbial activity and protein depolymerization. Here we show, from a global meta-analysis of 15N-labelled studies that gross N transformation rates in forest soil organic and mineral horizons differentially respond to N addition. In carbon (C)-rich organic horizons, N addition significantly enhanced soil gross rates of N mineralization, nitrification and microbial NO3¯ immobilization rates, but decreased gross microbial NH4+ immobilization rates. In C-poor mineral soils, in contrast, N addition did not change gross N transformation rates except for increasing gross nitrification rates. An initial soil C/N threshold of approx. 14.6, above which N addition enhanced gross N mineralization rates, could explain why gross N mineralization was increased by N deposition in organic horizons alone. Enhancement of gross N mineralization by N deposition was also largely attributed to enhanced N mineralization activity per unit microbial biomass. Our results indicate that the net effect of N input on forest soil gross N transformations are highly stratified by soil C distribution along the soil profile, and thus challenge the perception that N availability ubiquitously limits N mineralization. These findings suggest that these differences should be integrated into models to better predict forest ecosystem N cycle and C sequestration potential under future N deposition scenarios.
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