Contrasting responses of soil organic carbon dynamics to different nitrogen−addition approaches

Chronic atmospheric nitrogen (N) deposition caused by anthropogenic activities has dramatically affected terrestrial ecosystem carbon (C) cycling, especially in tropical and subtropical forests. Many studies based on experimental platform of understory N addition (UN) have proved that long-term N addition significantly stimulated the accumulation of soil organic carbon (SOC), especially particulate organic carbon (POC), but didn’t affect mineral-associated organic carbon (MAOC). On one hand, it may attribute to increased plant growth resulting from N addition, thereby enhancing C input from plant. On the other hand, because of soil acidification induced by N addition inhibited microbial C use efficiency. However, understory N addition may overlook various canopy processes, therefore, it may not fully reflect the effects of atmospheric N deposition on the C dynamics of forest ecosystems.

Based on the eleven−years of canopy and understory N addition experiment at Shimentai, we explored the contrasting effects of different N addition approaches on C dynamics and their mechanisms. Our results showed significantly different responses of SOC between the approaches, with UN displaying greater effects on SOC than CN. Specifically, both low and high rates of UN substantially increased the concentrations of POC, whereas the high rate of CN significantly increased those of MAOC rather than POC. It was possibly because that CN treatments significantly improved litter quality and mitigated soil acidification, thus stimulating microbial C utilization and accelerating the microbial transformation of POC to MAOC.

Our findings imply that the underlying mechanisms of natural N deposition influencing forest SOC may differ from those obtained from UN, and conventional fertilization experiments may overestimate the benefits of elevated N deposition to forest SOC.

The study titled "Contrasting responses of soil organic carbon dynamics to long-term canopy and understory nitrogen addition in a subtropical forest" was published online in Catena. Xiaofei Lu was first author of this paper and Professor Yuanwen Kuang was the corresponding author. This study was supported by National Natural Science Foundation of China, Key−Area Research and Development Program of Guangdong Province, Guangdong Flagship Project of Basic and Applied Basic Research, National Key Research and Development Program of China, Guangdong Science and Technology Plan Project.

The article link is: https://doi.org/10.1016/j.catena.2024.108536

First author information: Xiaofei Lu: Associate Professor., School of Environmental Science and Engineering, Nanjing University of Information Science & Technology, Research field: Forest ecology and C cycle, E-mail: luxf@nuist.edu.cn