Effects of Nitrogen Addition on Potential Soil Nitrogen-Cycling Processes in a Temperate Forest Ecosystem
2016
Sun, Jianfei | Peng, Bo | Li, Wei | Qu, Guifang | Dai, Weiwei | Dai, Guanhua | Jiang, Ping | Han, Shijie | Bai, Edith
Anthropogenic nitrogen (N) deposition substantially alters N cycling in terrestrial ecosystems because of its effects on soil physicochemical properties and soil microbes. Responses of N transformation processes to consecutive N additions are unclear, pointing to a lack of systematic understanding of N cycling under long-term N addition. This work combines N tracing laboratory incubation with the FLUAZ model to study potential gross N-cycling processes in a temperate forest ecosystem in eastern Asia after 6 years of consecutive N additions at a rate of 50 kg N ha year. Soils from plots that received N additions had greater gross N mineralization probably because of higher soil carbon (C) and N than soils from control plots. Gross nitrification in soil from plots receiving N additions was inhibited likely because of lower pH in these plots. Higher NH4 concentrations under N addition increased N immobilization by microbes, but NO3 immobilization was much lower than NH4 immobilization. Our results also show that N remineralization was stimulated by N addition and that microbes in N addition plots had greater N uptake probably because they adapted to high N concentration that led to accelerated microbial N turnover rate. This research highlights the importance of considering the effects of increasing N deposition on N processes mediated by microbes.
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