放牧对内蒙古典型草原α、β和γ多样性的影响机制

Mechanisms underlying the impacts of grazing on plant α, β and γ diversity in a typical steppe of the Inner Mongolia grassland

人类活动干扰对生物多样性和生态系统功能的影响机制是近年来生态学研究的一个热点问题。该研究以内蒙古锡林郭勒草原生态系统国家野外科学观测研究站的大型放牧控制实验为平台,系统地研究了不同降水(丰水年份和平水年份)和地形(平地和坡地)条件下,放牧对典型草原不同空间尺度植物多样性(α、β和γ多样性)的影响。研究发现:(1)降水和地形条件及其交互效应对植物多样性有明显的影响,丰水年份的α、β和γ多样性均高于平水年份;降水和地形条件存在交互效应,平水年份坡地系统的α多样性高于平地系统,丰水年份平地系统的α和γ多样性高于坡地系统,而地形对β多样性并没有显著影响;(2)随着放牧强度的增加,平地和坡地的α多样性均呈逐渐下降的趋势,不同植物群落成员型(优势种、常见种和稀有种)对放牧的响应及其对α多样性的贡献不同,其中稀有种对α多样性的贡献最大,常见种次之,优势种最小;(3)γ多样性对放牧强度的响应受地形条件的影响,随着放牧强度的增加,平地γ多样性呈逐渐下降的趋势,而坡地γ多样性呈现先减少后增加的趋势;(4)平地β多样性随放牧强度的增加而逐渐减小,而坡地并没有明显的规律。该研究表明,植物多样性对放牧的响应受降水和地形因素的调控,平地对放牧的缓冲能力强于坡地,干旱会加剧过度放牧对生物多样性的影响;稀有种对于草地生态系统的多样性维持具有重要意义。因此,在确定合理的放牧强度时,应结合降水和地形条件。在平水年份需加强平地系统植物多样性的保护,而在丰水年份需加强坡地系统植物多样性的保护,从而实现草地资源的可持续性利用。

Aims Human disturbance, such as overgrazing have resulted in widespread declines in biodiversity and ecosystem functioning and services in arid and semiarid grasslands worldwide. This study is aimed to examine the effects of grazing intensity, topography and precipitation fluctuation on plant diversity across three levels of organization （i.e., plant species, functional group, and community） in a typical steppe of the Inner Mongolia grassland. MethOds Based on a long-term grazing experiment maintained for eight years with seven levels of grazing in- tensity and two topographic systems in a typical steppe of the Inner Mongolia grassland, the effects of grazing intensity, topography （flat vs. slope）, and precipitation fluctuations （wet vs. normal years） on plant diversity （i.e. α, β and γ diversity） and their controlling mechanisms were examined. Important findings Our results showed that： （1） The diversity-grazing intensity relationship differed between two topographic systems and over two years （wet vs. normal years）. The α, β, and γ diversity in the wet year （2012） were higher than those in the normal year （2011）. ent on precipitation, with higher a diversity in the slope The effect of topography on plant diversity was depend- system and normal year and higher α and γ diversity in t, the flat system and wet year. There was no significant effect of topography on β diversity. （2） The α diversity de- creased with increasing grazing intensity in both the flat and slope systems. The α diversity response to grazing differed substantially among the dominant species, common species, and rare species in the two topographic sys- tems, with the highest negative response for rare species, intermediate negative response for common species, and the weakest response for dominant species. （3） In the flat system, 7 diversity declined with increasing grazing in- tensity, while it firstly decreased and then increased at the intermediate level of grazing intensity in the slope system. （4） The β diversity decreased with increasing grazing intensity in the flat system due to grazing-inducedspecies convergence, while it did not show any tendency in the slope system. Our results suggest that the topog- raphy and precipitation are two key factors governing the relationship between plant biodiversity and grazing in- tensity in the arid and semiarid grasslands. The loss of species in the dry year was greater in the fiat system than in the slope system, while the opposite result was found in the wet year. The rare species plays an important role in maintaining species diversity. These findings provide a better understanding of the biodiversity-grazing intensity relationship in the context of different precipitation and topographic conditions in the semiarid steppe and beyond.