Responses of the structure and health of plant and soil organism communities to canopy and understory nitrogen additions under a mature subtropical forest

The increase in human activity has caused a severe increase in the emission of N to the atmosphere and the effects of N deposition have been especially severe in tropical and subtropical areas. Forest was served as the main acceptor of atmospheric N deposition, and its responses have received wide interest. The majority of experiments now add N to the understory or floor directly, but there is still a debate about whether understory N addition can realistically simulate the natural process of atmospheric N deposition on forests. On the other hand, the responses of community structure indices to N addition showed complex synergism, trade-off and asynchronism, and there are no consensus patterns on the community health to N addition. Moreover, studies on the responses of soil organism communities are quite insufficient, compared to plant communities.

Ph.D student TIAN Yang from South China Botanical Garden of the Chinese Academy of Sciences, under the guidance of prof. LU Hongfang, conducted a study on the field experimental platform of canopy and understory N additions in the Shimentai National Nature Reserve, in order to determine the responses of structure indices and thermodynamic health of plant and soil organism communities to N treatments.

The results showed that richness in the shrub layer was more sensitive to the canopy N addition. Thus, previous studies adding N to the understory may underestimate the effects of N addition on the structure of forest communities. The results also found that the health status of the subtropical, evergreen, forest community as determined by thermodynamic measures was more sensitive to N addition compared to the classic community indices. After N treatments for 4 years, the results found that the structure indices and biomass of soil faunal communities were not significantly different from control. However, N treatments decreased the seasonal differences of soil microbial PLFAs.

Relevant researches were published in the Ecological Indicators and Science of the Total Environment, respectively. For further reading, please refer to: https://doi.org/10.1016/j.scitotenv.2020.137438 and https://doi.org/10.1016/j.ecolind.2019.105459.