Effects Of Long-term Grazing Intensity On CSR Strategies Of Stipa Breviflora Desert Steppe

Plant ecological strategy is the survival strategy adopted by plants to achieve the best adaptability in the environment of disturbance and stress,which is manifested by the changes of species morphology and physiological characteristics.CSR strategy(C,competitor strategy;S,stress-tolerator strategy;R,ruderal strategy)reflects the adaptability of plants to environmental stress and disturbance,and is the result of the interaction between plants and their environment.The ecological strategies adopted by a species will determine its niche in the community and ultimately affect ecosystem processes and functions.S.breviflora desert steppe is an important animal husbandry production base in China and an important ecological barrier in northern China.As the most important utilization method for desert steppe,grazing had profound effects on plant functional traits,survival strategies and soil nutrient cycling.In this experiment,the functional traits and CSR strategies of plants under different grazing intensities(no,light,moderate and heavy grazing)and their mechanisms were analyzed by using field ecological survey combined with indoor analysis in a S.breviflora desert steppe.The objectives were to provide basis for grassland grazing management and guide science for predicting the response of S.breviflora desert steppe to climate change and human disturbance.The main findings are follows:1.The species composition of the plant community in S.breviflora desert steppe changed under different grazing intensities.Compared with enclosure,the number of community species decreased with grazing intensity,and the number of community species decreased with the increase of grazing intensity.2.Compared with enclosure,grazing significantly decreased fresh leaf weight,dry leaf weight,leaf water content,specific leaf area and transpiration rate;Moderate and heavy grazing significantly decreased the net photosynthetic rate;Heavy grazing significantly reduced litter area.Grazing significantly increased leaf dry matter content.The leaf area,fresh and dry weight,net photosynthetic rate and transpiration rate of perennial grasses,perennial forbs,shrubs and semi-shrubs and annual and biennials all showed a decreasing trend with the increase of grazing intensity.Leaf water content,dry matter content and specific leaf area increased with the increase of grazing intensity in perennial forbs and shrubs and semi-shrubs.3.In the desert steppe of S.breviflora,C:S:R= 1.98:47.78:50.24% in the enclosure,C:S:R= 2.22:54.17:43.61% in the light grazing,C:S:R=2.35:54.71:42.94% in the medium grazing,C:S:R= 2.31:59.04: 38.65% heavy grazing.With the increase of grazing intensity,the plants gradually shifted to the more stress-tolerant S strategy,indicating that the plants responded to grazing disturbance by increasing their own tolerance.Leaf dry matter content,leaf water content and specific leaf area were the main factors affecting S and R strategies of S.breviflora in desert steppe.4.The effects of grazing intensity on soil physicochemical properties were different.Grazing significantly reduced soil total phosphorus and available phosphorus;Moderate and heavy grazing significantly decreased soil organic carbon and water content,and significantly increased soil compaction and bulk density.The redundancy analysis showed that soil bulk and compaction positively regulated the S strategy and negatively regulated the R strategy.In contrast,soil effective phosphorus,soil total nitrogen and soil organic carbon were negatively regulated by the S strategy and positively regulated by the R strategy,indicating that soil bulk and compaction as well as soil nutrients were the main soil environmental factors regulating the CSR strategy of S.breviflora desert grassland.The results of this study showed that in S.breviflora desert steppe,plants adopted more stress-tolerant survival strategies(S strategy)in response to grazing disturbance,and the proportion of S strategies increased with the increase of grazing intensities.This study provide scientific basis for the sustainable development of desert steppe and theoretical guidance for predicting the response of desert steppe to climate change and human disturbance in the future.