Human activities have substantially altered global nitrogen (N) cycling, resulting in large amounts of reactive N being deposited into terrestrial ecosystems. The enhancement of reactive N availability threatens plant diversity in diverse ecosystems. While the composition of deposition N compounds is very complex, the variation of their effects on species diversity has received less attention.  

Moreover, there is mounting evidence for the negative impacts of N deposition on one component of diversity, species richness, we know little about its effects on another one, species evenness. 

It is suspected that hay-harvesting by mowing in grasslands would remove nitrogen from the ecosystem and thus would mitigate the negative impacts of N deposition on plant diversity. Empirical evidence, however, is scarce.  

To investigate the main and interactive effects of N addition (both rates and forms) and mowing on plant diversity, Prof. LV Xiaotao and Dr. YANG Guojiao from Institute of Applied Ecology of the Chinese Academy of Sciences carried out a four-year field experiment in a temperate meadow steppe in northeastern China. 

The results showed that species richness and evenness were negatively correlated with N addition rate across all the types of N compounds.

The magnitude of such responses varied significantly among different compounds, with (NH₄)₂SO₄ addition resulting in the lowest richness and evenness. Interestingly, mowing mitigate the negative impacts of N deposition on species diversity.  

The results present robust evidence that N deposition threatens biodiversity by reducing both species richness and evenness, a process which could be alleviated by mowing. This study highlights the important role of ecosystem management practice in mediating the impacts of N deposition on plant diversity. 

This study was published in Oecologia entitled "Mowing mitigates the negative impacts of N addition on plant species diversity".   

This study was supported by the Natural Science Foundation of China, the Strategic Priority Research Program of the Chinese Academy of Sciences and the Youth Innovation Promotion Association CAS.  

Experimental Setup in Erguna grassland (Image by IAE)