Center for Ecological and Environmental Sciences, South China Botanical Garden, Chinese Academy of Sciences, 723 Xingke Rd., Tianhe District, Guangzhou 510650, China; University of Chinese Academy of Sciences, Beijing 100049, China.
Center for Ecological and Environmental Sciences, South China Botanical Garden, Chinese Academy of Sciences, 723 Xingke Rd., Tianhe District, Guangzhou 510650, China.
Sci Total Environ. 2018 Jun 1;626:1175-1187. doi: 10.1016/j.scitotenv.2018.01.132. Epub 2018 Feb 19.
Atmospherically-deposited nitrogen (N) can stimulate complex soil N metabolisms and accumulations over time. Whether long-term (decadal) N deposition effects on soil N transformations and functional microbes differ from the short-term (annual) effects has rarely been assessed. Here we conducted a laboratory N tracing study with soil samples from a short-term (one year) N addition site and a long-term (12 years) site in a subtropical forest. The effects of simulated N deposition on soil NO emissions, N transformation rates and microbial nitrifying and denitrifying genes were determined. Our results showed that: (1) long-term N addition did not change soil NO fluxes significantly in comparison to the short-term N addition. Denitrification, heterotrophic nitrification and autotrophic nitrification contributed 53%, 28% and 18% to total NO emissions, respectively. (2) Autotrophic nitrification was the dominant N transformation process, except for the high-N treatment at the long-term site. The magnitude of soil N transformation rates was significantly different among N addition treatments but not between short- and long-term N addition sites. However, long-term N addition changed the responses of specific N transformation rates to N addition markedly, especially for the rates of nitrification, organic N mineralization to NH, NO immobilization and dissimilatory NO reduction to NH (DNRA). (3) Responses of ammonia oxidizing archaea and bacteria (AOA and AOB) were more variable than those of denitrifying NO-producers (nirK) and denitrifying NO-reducers (nosZ), particularly at the long-term site. (4) The close correlations among NO flux, functional genes and soil properties observed at the short-term site were weakened at the long-term site, posing a decreased risk for N losses in the acid subtropical forest soil. There is evidence for an adaptation of functional microbial communities to the prevailing soil conditions and in response to long-term natural and anthropogenic N depositions.
大气氮（N）可以随时间推移刺激复杂的土壤 N 代谢和积累。长期（数十年）氮沉积对土壤 N 转化和功能微生物的影响是否与短期（每年）不同，这很少被评估。在这里，我们利用亚热带森林中短期（一年）氮添加地点和长期（12 年）地点的土壤样本进行了实验室氮示踪研究。测定了模拟氮沉积对土壤 NO 排放、N 转化速率以及微生物硝化和反硝化基因的影响。我们的结果表明：（1）与短期氮添加相比，长期氮添加对土壤 NO 通量没有显著影响。反硝化、异养硝化和自养硝化分别对总 NO 排放贡献 53%、28%和 18%。（2）自养硝化是主要的 N 转化过程，除了长期地点的高氮处理外。氮添加处理之间土壤 N 转化速率的幅度差异显著，但短期和长期氮添加地点之间没有差异。然而，长期氮添加显著改变了特定 N 转化速率对氮添加的响应，特别是硝化、有机 N 矿化到 NH、NO 固定和异化 NO 还原到 NH（DNRA）的速率。（3）氨氧化古菌和细菌（AOA 和 AOB）的响应比反硝化 NO 生产者（nirK）和反硝化 NO 还原酶（nosZ）更具变异性，尤其是在长期地点。（4）在短期地点观察到的 NO 通量、功能基因和土壤特性之间的密切相关性在长期地点减弱，这降低了酸性亚热带森林土壤中 N 损失的风险。有证据表明功能微生物群落适应了流行的土壤条件，并对长期自然和人为氮沉积做出了响应。
