Human activities have resulted in serious atmospheric nitrogen deposition in large-scale areas of the world. The reactive nitrogen deposited into forest ecosystems provides nutrient available to plants and microbes, which further affects their growth, biomass accumulation, and carbon emission via respiration. Although nitrogen deposition can regulate soil respiration in forest ecosystems, the relevant knowledge is derived mainly from short-term manipulative experiments. It remains unclear how nitrogen deposition affects soil respiration with time in tropical and subtropical forests.

In the earliest nitrogen-deposition research platforms of Chinese forest ecosystems (nitrogen-addition plots in Dinghushan forests), the Ecosystem Management Research Team (Dr. ZHENG Mianhai, Dr. ZHANG Wei, Prof. Mo Jiangming, and other members) discovered three-phase patterns of soil CO₂ emission (insignificant changes - dramatic decline - insignificant changes). In the first phase, they observed less response of plant and microbial carbon and nitrogen variables under nitrogen addition treatments, and soil respiration responses did not change. During the second phase, nitrogen addition caused obvious soil acidification, which led to death of fine roots and decrease of soil microbial biomass, and thus soil respiration dramatically declined. After entering the third phase, plant and microbial communities might reorganize, and they observed less change in fine root biomass, soil microbial biomass, and soil respiration rates under nitrogen addition treatments.

Overall, their results show that the responses of soil respiration to nitrogen deposition do not remain stable but can alter with time in the study forests. This phenomenon cannot be captured by short-term experiment studies, and it advances scientific understanding of soil respiration dynamics and support prediction of soil carbon fluxes under nitrogen deposition scenarios. These findings have been published in Nature Geoscience (https://www.nature.com/articles/s41561-022-01080-4)

Author: ZHENG Mianhai

E-mail: zhengmianhai@scbg.ac.cn

Paper link: https://www.nature.com/articles/s41561-022-01080-4

Online time: 01 December 2022

Figure. Conceptual framework of soil respiration response to long-term nitrogen addition.