Net primary productivity (NPP) is the fundamental ecosystem function, which could be partitioned into above-ground NPP (ANPP) and below-ground NPP (BNPP). It is important to estimate the change of BNPP to climate change, as it accounts for 64% of grassland NPP. Although atmospheric nitrogen deposition is increasing globally, our understanding of its impact on BNPP is rather limited.  

Temporal stability of NPP is important for predicting the sustainable provisioning of ecosystem services. Many studies have reported a negative impacts of nitrogen enrichment on the temporal stability of ANPP, it is unclear whether BNPP and NPP would show similar responses. Answering this question may help in projecting ecosystem services. 

A research group led by Prof. LV Xiaotao from the Institute of Applied Ecology of the Chinese Academy of Sciences conducted a nitrogen addition manipulation experiment in the Erguna Forest-Steppe Ecotone Research Station of Inner Mongolia. They explored the impacts of nitrogen addition on the temporal stability of ANPP, BNPP, and NPP and their associated mechanisms at two different spatial scales. 

According to the researchers, nitrogen addition significantly decreased ANPP stability both at the local and larger spatial scale due to nitrogen-induced reduction in species diversity, but did not affect the stability of BNPP and NPP at both scales.

Additionally, BNPP was responsible for the responses of NPP to nitrogen enrichment. They found that spatial asynchrony of both ANPP and BNPP among communities was not affected by nitrogen addition, which provided greater stability at the larger scale.  

These findings challenge the perspective that nitrogen addition would destabilize primary productivity based on results only from aboveground, and highlight the importance of a whole ecosystem perspective. 

This study, supported by the Natural Science Foundation of China, was published in Global Change Biology entitled "Decoupled responses of above- and below-ground stability of productivity to nitrogen addition at the local and larger spatial scale". 

Structural equation modelling showing the direct and indirect effects of N enrichment on grassland biodiversity and ecosystem stability at multiple scales. (Image by YANG Guojiao)