Since the industrial revolution, atmospheric active nitrogen (N) deposition has continued to increase worldwide due to human activities. N is considered as an essential element for ecosystem, and anthropogenic N deposition has been found to influence many aspects of forest ecosystems, such as soil acidity, the fate, cycle, and storage of soil carbon (C). It is very important to understand the changes in forest soil C and the potential mechanisms as forest soil holds a large C storage and plays a significant role in global C cycle and global warming. However, the direct, extent, and mechanism of the effects of N deposition on forest carbon are still unclear. Based on an experimental N‐addition treatment conducted in a montane forest, we found that short‐term N addition could increase soil storage in the aggregate fraction but not in the bulk soil. N‐induced SOC accumulation was partly associated with the suppressed SOC decomposition (indicated by lower soil respiration) that resulted from the reduced microbial biomass rather than from decreased lignin‐degrading enzyme activity or from reduced soil acidity. In addition, N addition promoted soil aggregate formation, which could partly suppress SOC decomposition by protecting new carbon that originated from plant litter residue to a greater degree, while dissolved organic carbon retention in the mineral soils played a limited role in the SOC sequestration derived from N addition, at least in the short term. A conceptual model was proposed and highlighted a new underlying mechanism of new carbon protection by enhanced aggregate formation, other than the role of microbial suppression, to explain the positive effect of anthropogenic N deposition on forest SOC.
This study has been supported by the National Key Research and Development Program of China (2016YFC0502105); Key Research Program of Frontier Sciences, CAS (QYZDJ‐SSW‐DQC006); the Youth Innovation Promotion Association CAS (2018406). This study entitled Anthropogenic Nitrogen Deposition Increases Soil Carbon by Enhancing New Carbon of the Soil Aggregate Formation has been published online in Journal of Geophysical Research: Biogeosciences.
Figure 1. A conceptual model presents the response of soil organic carbon (SOC) to N addition and the potential mechanisms driving the SOC accumulation in the organic and mineral layers(Image by CHANG Ruiying).
Institute of Mountain Hazards and Environment, Chinese Academy of Sciences
Chengdu, Sichuan, 610041, China