Global nitrogen (N) deposition generally reduces plant biodiversity and changes ecosystem C sequestration. Light competition caused by accumulated standing litter under N enrichment would change the responses of ecosystem biodiversity and ecosystem C sequestration. Unfortunately, the observed effects of light limitation on biodiversity and ecosystem C sequestration are still limited and controversial, and mechanisms underlying this light competition effect are not well understood yet under different N addition gradients. Therefore, more studies on how species diversity and ecosystem C sequestration respond to light competition of different intensity under N enrichment are needed to resolve the disputes. We carried out a field manipulation experiment with N addition as the primary factor nested with litter manipulation as the secondary factor in an alpine meadow on the Qinghai-Tibetan Plateau in 2017, to test the response of biodiversity and ecosystem C sequestration to litter manipulation and N addition, and reveal the potential mechanisms of light competition affecting biodiversity and C sequestration under N enrichment.
Results/Conclusions
Our results found that alleviation of light competition increased species richness under N enrichment, which caused by higher species gains and lower species losses. Common and rare species contributed most of the increased species as light competition is relieved. N addition had no significant effect on NEP, whereas alleviation of light competition under N enrichment stimulated GPP but did not affect ER, causing positive responses of NEP. This study highlights the catalytic effect of light mitigation on species diversity and ecosystem C sequestration under N enrichment. Both species gain and loss contributed to the dynamic change of species richness when light competition coexists with N fertilization, and the change of ecosystem C sequestration under light competition was mainly determined by photosynthesis responses. These findings provide new insights into the mechanisms underlying light competition effects on biodiversity and ecosystem C sequestration under N enrichment. We suggest that grassland management by removing the accumulated standing litter is essential for mitigating diversity loss and increasing C sequestration under eutrophication.