Knowledge about arbuscular mycorrhizal fungi (AMF) is crucial for understanding nutrient limitations on primary productivity and soil organic carbon (C) storage in terrestrial ecosystems. Both theoretical models and empirical evidence hold that nitrogen (N) addition in phosphorus-limited ecosystems can either increase or decrease AMF diversity and abundance. However, many of these studies involved high-level N additions, which do not reflect realistic levels of atmospheric N deposition, thus leading to biased estimations of AMF and their role in the soil C stock.

The Ecosystem Management research group, led by Principal Investigator Dr. ZHENG Mianhai at the South China Botanical Garden, Chinese Academy of Sciences, utilizes experimental platforms at Dinghushan and Heshan to assess AMF diversity and abundance under nitrogen addition. This research draws on data from five tropical forests, with arbuscular mycorrhizal tree dominance ranging from 88%, 31%, and 25% to dual-mycorrhizal tree dominance, and integrates these findings with a global synthesis of tropical and subtropical forests. The results of field study showed that N addition based on realistic N deposition (≤50 kg N ha⁻¹ yr⁻¹, comparable to the actual rate of atmospheric N deposition in the studied sites) caused little change in AMF abundance and diversity, as confirmed by meta-analysis. The responses of AMF abundance to N addition did not differ significantly across forests with varying mycorrhizal dominance. However, high-level N addition (>50 kg N ha⁻¹ yr⁻¹) from a global dataset reduced AMF abundance and diversity. AMF responses were correlated with plant C, soil nutrient availability, and/or pH. The findings further indicate that current atmospheric N deposition is unlikely to enhance soil C content via AMF. Given that N deposition has been stable or even declined in major global economies, they propose that previous studies may have overestimated AMF responses to atmospheric N deposition, which neither increased nor reduced AMF abundance and diversity as previously thought.

The above studies, entitled ‘Atmospheric nitrogen deposition has minor impacts on the abundance and diversity of arbuscular mycorrhizal fungi and their contribution to soil carbon stock in tropical forests’, was published in Soil Biology and Biochemistry. This research was supported by Guangdong Basic and Applied Basic Research Foundation, National Key Research and Development Program of China, Youth Innovation Promotion Association of the Chinese Academy of Sciences, South China Botanical Garden, Chinese Academy of Sciences, Science and Technology Projects in Guangzhou, China Postdoctoral Science Foundation, and China Scholarship Council.

Paper link: https://www.sciencedirect.com/science/article/pii/S0038071725000380

Figure 1. Conceptual diagram of the effects of atmospheric nitrogen deposition on the abundance and diversity of AMF and soil organic carbon stock in tropical forests.

Figure 2. The effects of nitrogen addition on AMF abundance and diversity, as well as soil organic carbon, in Dinghushan and Heshan forests.