放牧对草地土壤氮素循环关键过程的影响与机制研究进展

Effects and mechanisms of grazing on key processes of soil nitrogen cycling in grassland: A review

放牧是人类管理利用草地生态系统的最主要途径之一.食草动物的采食、践踏、卧息和排泄物归还等干扰不仅会改变草地地上植物群落,也会对土壤养分循环产生显著的影响.随着人类活动的加剧,放牧强度和频率也在逐渐增加,从而对草地土壤氮素循环关键过程产生重要影响.放牧主要通过改变土壤的物理性质、土壤氮库以及微生物的组成和结构,进而影响氮素在土壤中的迁移与转化.适度放牧会促进土壤氮素的矿化过程和硝化过程,加快氮素的周转,有利于植物吸收可利用氮素,而对于反硝化的影响与草地的水热条件和土壤类型等密切相关.目前,关于放牧强度对土壤氮素循环关键过程影响的研究结果不一致,其影响机制尚不明晰,尤其对于不同类型的草原仍存在较大的差异.本研究在大量查阅国内外已有研究结果的基础上,论述了放牧对土壤氮素循环关键过程的影响效应,总结了放牧对土壤氮素循环的影响机制,指出了目前研究过程中存在的不足,并对未来研究中值得重点关注和深入研究的科学问题进行了探讨与展望,为进一步理解放牧对草地土壤氮素循环的影响提供参考.

Grazing is one of the most important practices for humans to manage grassland ecosystems.The disturbances of feeding,trampling,resting and excreta returning by herbivores will change plant communities and soil nutrient cycling.With the intensification of human activities,the intensity and frequency of grazing were also increased,which would have important impacts on the key processes of soil nitrogen(N)cycling in grassland.Grazing mainly affects the migration and transformation of N in soils by changing soil physical properties,soil N pool size,as well as the composition and structure of soil microbial community.Generally,moderate grazing could enhance soil N mineralization and nitrification,accelerate soil N turnover,and facilitate plant N use.The effects of grazing on denitrification are closely related to the hydrothermal conditions and soil types.Current results on the effects of grazing intensity on various key processes of soil N cycling remain inconsistent,with underlying mechanism being not clear.Based on extensive review of literature,we summarized the research progresses and the underlying mechanisms of the effects of grazing on key processes of soil N cycling.Some deficiencies in current research were pointed out.Possible key topics in the future study were proposed to provide a reference for further understanding the impacts of grazing on soil N cycling in grasslands.