National Forestry and Grassland Administration Key Laboratory of Forest Resources Conservation and Ecological Safety on the Upper Reaches of the Yangtze River, Forestry Ecological Engineering in the Upper Reaches of the Yangtze River Key Laboratory of Sichuan Province, College of Forestry, Sichuan Agricultural University, Chengdu, Sichuan, 611130, China.
Maize Research Institute, Sichuan Agricultural University, Chengdu, Sichuan, 611130, China.
J Environ Manage. 2023 Dec 15;348:119274. doi: 10.1016/j.jenvman.2023.119274. Epub 2023 Oct 25.
Microbially driven nitrification and denitrification play important roles in regulating soil N availability and NO emissions. However, how the composition of nitrifying and denitrifying prokaryotic communities respond to long-term N additions and regulate soil NO emissions in subtropical forests remains unclear. Seven years of field experiment which included three N treatments (+0, +50, +150 kg N ha yr; CK, LN, HN) was conducted in a subtropical forest. Soil available nutrients, NO emissions, net N mineralization, denitrification potential and enzyme activities, and the composition and diversity of nitrifying and denitrifying communities were measured. Soil NO emissions from the LN and HN treatments increased by 42.37% and 243.32%, respectively, as compared to the CK. Nitrogen addition significantly inhibited nitrification (N mineralization) and significantly increased denitrification potentials and enzymes. Nitrification and denitrification abundances (except nirK) were significantly lower in the HN, than CK treatment and were not significantly correlated with NO emissions. Nitrogen addition significantly increased nirK abundance while maintaining the positive effects of denitrification and NO emissions to N deposition, challenging the conventional wisdom that long-term N addition reduces NO emissions by inhibiting microbial growth. Structural equation modeling showed that the composition, diversity, and abundance of nirS- and nirK-type denitrifying prokaryotic communities had direct effects on NO emissions. Mechanistic investigations have revealed that denitrifier keystone taxa transitioned from NO-reducing (complete denitrification) to NO-producing (incomplete denitrification) with increasing N addition, increasing structural complexity and diversity of the denitrifier co-occurrence network. These results significantly advance current understanding of the relationship between denitrifying community composition and NO emissions, and highlight the importance of incorporating denitrifying community dynamics and soil environmental factors together in models to accurately predict key ecosystem processes under global change.
微生物驱动的硝化和反硝化在调节土壤氮素有效性和 NO 排放方面发挥着重要作用。然而，硝化和反硝化原核生物群落的组成如何响应长期氮添加以及调节亚热带森林土壤 NO 排放仍不清楚。在亚热带森林中进行了为期 7 年的田间实验，包括 3 种氮处理（+0、+50、+150 kg N ha-1 yr-1；CK、LN、HN）。测量了土壤有效养分、NO 排放、净氮矿化、反硝化潜力和酶活性以及硝化和反硝化群落的组成和多样性。与 CK 相比，LN 和 HN 处理的土壤 NO 排放量分别增加了 42.37%和 243.32%。氮添加显著抑制了硝化（氮矿化）并显著增加了反硝化潜力和酶。硝化和反硝化丰度（除 nirK 外）在 HN 处理中明显低于 CK 处理，且与 NO 排放无显著相关性。氮添加显著增加了 nirK 丰度，同时保持了反硝化和 NO 排放对氮沉降的积极影响，这挑战了长期氮添加通过抑制微生物生长而减少 NO 排放的传统观点。结构方程模型表明，nirS 和 nirK 型反硝化原核生物群落的组成、多样性和丰度对 NO 排放有直接影响。机制研究表明，随着氮添加量的增加，反硝化菌关键类群从硝酸盐还原（完全反硝化）转变为硝酸盐产生（不完全反硝化），增加了反硝化共生网络的结构复杂性和多样性。这些结果显著提高了对反硝化群落组成与 NO 排放之间关系的认识，并强调了在模型中综合考虑反硝化群落动态和土壤环境因素以准确预测全球变化下关键生态系统过程的重要性。
