Sen Yang, Weixing Liu, Chunlian Qiao, Jing Wang, Meifeng Deng, Beibei Zhang, Lingli Liu

Increasing nitrogen (N) deposition is not only altering plant chemical composition, but also resulting in worldwide biodiversity loss. However, few field studies have explicitly evaluated how the physiological response of individual species and changes in plant community composition may combine to affect key ecosystem functions such as soil carbon sequestration.

Liu - 00010 - graphical abstractWe conducted field observations and sampling in a long-term N addition grassland site in Inner Mongolia. We measured soil heterotrophic respiration (respiration by soil microbes, Rh), aboveground biomass, mass of the litter layer and soil properties from 2014 to 2016. Plant community composition was investigated in early August each year. Litter chemical composition was analyzed both through wet chemical method and 13C-CPMAS nuclear magnetic resonance  spectroscopy.

Our results indicated that N addition significantly decreased Rh and increased litter residence time. N addition decreased the degradability of most plant species, and the abundance of relatively highly degradable species declined rapidly. The increase in chemical recalcitrance of individual species and loss of highly degradable species significantly decreased litter degradability at the community level. Our results indicated that the loss of plant diversity and the decrease in community level litter degradability jointly best explained the reduction of Rh following N addition.

Overall, we demonstrated that plant diversity loss under increasing N deposition could slow soil carbon cycling. We emphasis the importance of incorporating plant composition dynamics into understanding how the soil carbon cycle will respond to global changes.

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