Effects Of Grazing And Hydrothermal Condition On Quantitative Characteristics Of Plant Community In Stipa Breviflora Desert Steppe

Stipa breviflora desert steppe,acts as a transitional zone between grassland and desert and an important component of semi-arid grassland of Eurasia,is a very fragile grassland ecosystem and sensitive to environmental changes.Grazing,which plays an important role in regulating grassland ecosystem,is the important way of grassland resource utilization in this kind of grassland.Thus studying the effect of grazing utilizations and hydrothermal conditions on plant community characteristics in desert steppe will contribute to understand the ecological response and self-regulation mechanism of grassland plants to grazing utilization and hydrothermal changes,and it is of great significance for protecting grassland ecological environment and rationally utilizing grassland resources in desert steppe.In this study,Stipa breviflora desert steppe in Siziwang Banner of Inner Mongolia was used as a sample plot.Based on the long-term monitoring of the grassland plant community quantitative characteristics and meteorological factors,the relationships between plant community quantitative characteristics,plant community and hydrothermal factors,and the state pattern and transfer process among various plant functional groups in grassland ecosystem were detected under no grazing and heavy grazing treatment.Accordingly,the regulation and influence mechanism of grazing utilization and water-heat change on desert steppe ecosystem is revealed.Based on data analysis of long-term grazing experiment from 2005 to 2015,mainresults in the present study are summarized as follows:1.Observations on the time-lag and cumulative effects of hydrothermal conditions on the plant community quantitative characteristics show that the time-lag and cumulative response of the plant community quantitative characteristics to precipitation varies at different growth stages.Heavy grazing reduced the response of species richness(SR),community coverage(CC)and community height(CH)to water-heat coupling,but it had little effect on the time-lag and cumulative response of the above-ground standing crop(AGSC)to precipitation in the growing season(the time-lag period was I month,the cumulative periods were 2 months)during the peak period of grass production.2.The correlation pattern between the plant community quantitative characteristics and hydrothermal conditions were not changed under heavy grazing.Whether in no grazing or heavy grazing sites,the AGSC,CC and CH are positively correlated with accumulated precipitation and negatively correlated with accumulated temperature,and the SR is positively correlated with accumulated precipitation and temperature.However,the marginal effect of cumulative precipitation on AGSC,CC and CH is weakened under heavy grazing.3.The plant community quantitative characteristics are influenced by grazing utilization and precipitation year types.Whether in no grazing or heavy grazing sites,the plant community quantitative characteristics in wet years were significantly greater than those in dry years.Regardless of the type of precipitation year,the plant community quantitative characteristics in no grazing sites are significantly greater than those in heavy grazing sites.However,the correlation properties between the plant community quantitative characteristics are not affected by grazing treatments and precipitation year types,and there is always a linear positive correlation between any two terms.4.Grazing differently influences variance explanation proportions of water and heat conditions to the plant community quantitative characteristics.Whether in no grazing or heavy grazing sites,the influence of water conditions on the AGSC,CC and CH is always greater than that of temperature conditions.However,heavy grazing significantly reduced the variance explanation proportions of water and heat condition on SR.In addition,the effect of water conditions on SR in no grazing sites was greater than that of heat conditions,and the effect of heat conditions on SR in heavy grazing areas was greater than that of water conditions.5.There is a significant impact of heavy grazing and precipitation year types on the inter-annual state pattern and transfer process of plant functional groups.On the one hand,long-term,continuous heavy grazing does not affect the proportion of C3 plants and dominant plants in the community,or increase the proportion of gramineae plants in the communityand reduce the proportion of woody plants in the community.On the other hand,when the wet year turns to normal or dry year,heavy grazing promotes the transfer of plants from C4 to C3,from non-dominant to dominant,and from non-gramineous to gramineous.When the dry year or normal year turns to wet year,however,heavy grazing promotes the transfer of plants from the reversed direction.In addition,the cumulative effect of long-term heavy grazing on the transfer of from woody plants to herbaceous plants is presented as a positive effect regardless of precipitation year types.It was found that precipitation is the dominant factor of community characteristics in Stipa breviflora desert steppe in this study.Long-term heavy grazing has little effect on the relationship between plant community characteristics and water-heat conditions,but it has significant effect on the state pattern and transfer process among different plant functional groups.The change of the state pattern of plant functional groups will further affect the structure and function of ecosystem in Stipa breviflora desert steppe.Therefore,it is of great significance to study the impacts of grazing utilization and hydrothermal changes on grassland ecosystem functions for the protection and sustainable utilization of grassland resources.