%0 Journal Article %A Yuan-He YANG %A Dian-Ye ZHANG %A Bin WEI %A Yang LIU %A Xue-Hui FENG %A Chao MAO %A Wei-Jie XU %A Mei HE %A Lu WANG %A Zhi-Hu ZHENG %A Yuan-Yuan WANG %A Lei-Yi CHEN %A Yun-Feng PENG %T Nonlinear responses of community diversity, carbon and nitrogen cycles of grassland ecosystems to external nitrogen input %D 2023 %R 10.17521/cjpe.2022.0107 %J Chinese Journal of Plant Ecology %P 1-24 %V 47 %N 1 %X

Understanding the response patterns and potential mechanisms of structure and function in grassland ecosystems to nitrogen (N) enrichment is essential to evaluate ecological impacts of external N input. The muti-level N manipulative experiment offers the possibility to explore the nonlinear response patterns and associated mechanisms of structure and function in grassland ecosystems to additional N input. In this review, we summarized the impacts of additional N inputs on community diversity, carbon (C) and N cycling in grassland ecosystems around the world. Numerous studies illustrated that N enrichment induced the decline of plant species diversity, plant functional diversity and soil bacteria richness in grassland ecosystems, yet the change of fungal diversity was not significant. Above- and below-ground plant productivity showed different responses to N input: aboveground plant productivity exhibited initial increasing and subsequent saturation trends, but root productivity and root:shoot ratio showed downward patterns, and root turnover rate appeared a single-peak pattern of first increasing and then decreasing with the continuous increase of N addition rate. Meanwhile, different C decomposition processes responded variously to N enrichment. Specifically, litter decomposition rates exhibited multiple response of “exponential decrease, liner increase or insignificant change with N addition level”. However, the relationship of soil respiration and CH4 consumption with N addition was dominated by a single peak trend of increasing at low to medium N levels but declining at high N levels. Likewise, different soil C fractions showed multiple response patterns to N input. N addition generally stimulated soil C storage and particulate organic C accumulation, while the mineral-associated organic C exhibited divergent responses of “increase, unaltered, and decrease” along the N addition gradient. In addition, plant N uptake exhibited initial increasing and subsequent situation trends along N addition gradients, while different soil N transformation processes showed differentiated responses along N addition gradients and the relationship between N2O emission and N addition rate varied among various grassland ecosystems. An exponential increase of N2O fluxes with N addition rate was observed in temperate grasslands, while the patterns of first increase and then saturation or linear increase of the N-induced changes in N2O emissions had been discovered in alpine grasslands. Future studies should focus on the nonlinear responses of rhizosphere processes and phosphorus (P) cycle to external N input, and also explore potential mechanisms from the aspect of multi-dimensional biodiversity changes.

%U https://www.plant-ecology.com/EN/10.17521/cjpe.2022.0107