The Innovation Team of Grassland Ecology and Remote Sensing of the Institute of Agricultural Resources and Regional Planning (IARRP) of the Chinese Academy of Agricultural Sciences (CAAS) made important progress in the study of nitrogen deposition effects. The study found that there will be deviations in predicting the effects of nitrogen deposition based on either organic or inorganic nitrogen addition experiment.

The relevant research results were published in Global Change Biology, a TOP journal in the Q1 area of ecology.

The chemical composition of deposited nitrogen includes inorganic nitrogen (IN) and organic nitrogen (ON), and these nitrogen sources may have different impacts on ecosystems. However, our understanding of the nitrogen deposition effect is mainly based on experimental gradients of INs or more rarely ONs. Thus, our understanding of how nitrogen deposition affects ecosystem productivity and biodiversity may be biased.

In this study, long-term nitrogen addition experiments with different IN:ON ratios (0:10, 3:7, 5:5, 7:3 and 10:0) were carried out on a typical temperate grassland to explore the effects of IN:ON ratios on plant community productivity and plant diversity.

In addition, the researchers also measured soil pH, litter biomass, soil IN concentration, and light penetration to dissect the underlying mechanism of species loss caused by nitrogen addition.

The results of the study found that nitrogen addition significantly increased plant community productivity by 68.33-105.50% and decreased species richness by 16.20-37.99%. The IN:ON ratios had no significant effect on plant community productivity. However, the species richness loss caused by IN was about 2.34 times that caused by ON. Soil pH was positively correlated with species richness, and they showed very similar response patterns to IN:ON ratios. It implies that soil acidification accounts for the different magnitudes of species loss with IN and ON additions. Overall, this study suggests that it may be reasonable to assess the effect of nitrogen deposition on plant community productivity by adding IN or ON. However, the evaluation of N deposition on biodiversity might be overestimated if only IN is added or underestimated if only ON is added.

Ke Yuguang, a doctoral student at the IARRP, is the first author, and researcher Yu Qiang is the corresponding author. This research was co-funded by the National Key Research and Development Project (2017YFA0604802) and the National Natural Science Foundation of China (31270476).

Paper link: https://onlinelibrary.wiley.com/doi/abs/10.1111/gcb.16530 

Effects of nitrogen addition with different IN:ON ratios on plant community productivity (ANPP) (a), species richness (b) and soil pH (c) and the linear relationship between species richness and soil pH (d). [Photo/IARRP]