Water Source And Water Use Efficiency Of Dominant Plant Species In Seasonal Grazing Typical Steppe

Seasonal grazing is the basic form of traditional grass husbandry management and an important aspect of constructing a modern sustainable grassland grazing system.In the typical grassland area of Inner Mongolia,the research on grazing systems mostly focuses on different grazing intensities,while the ecological and production effects of seasonal grazing are less studied,especially the lack of research on the impact of seasonal grazing on the water use of plant communities.In this paper,taking a typical grassland in Inner Mongolia as an example,using hydrogen,oxygen,and carbon stable isotope technology and infrared gas exchange method to determine and analyze the dominant species of Leymus chinensis,Stipa grandis and Rhizome The water source,response to different precipitation events and water use efficiency characteristics of Zigrass;it is helpful to understand the water adaptation mechanism of typical grassland ecosystems to seasonal grazing at the species level.The main research results are as follows:1.Seasonal grazing treatment,sampling time,soil depth,and the interaction between sampling time and soil depth.The interaction between sampling time and seasonal grazing has a significant impact on soil moisture content（P<0.01）.The monthly dynamic trend of soil moisture content under different seasons of grazing treatments is relatively consistent.The soil moisture content is higher in May and August,and reaches the lowest in June;the different seasonal grazing plots are 20-50cm from May to September.The moisture content of the soil layer is higher than other soil layers as a whole.The soil moisture content of 0-20cm varies greatly before and after rainfall.2.Summer grazing treatments significantly reduced the relative aboveground biomass of Cleistogenes squarrosa scabra in the early growing season（May）（P<0.05）;autumn grazing treatments significantly reduced the relative aboveground biomass of Stipa grandis in the early growing season（P<0.05）.The relative above-ground biomass of Leymus chinensis was significantly increased（P<0.05）in the peak growing season（August）of the sample plots treated with summer grazing（P<0.05）,and the relative above-ground biomass of C.scabra significantly decreased（P<0.05）.There was no significant difference in the relative aboveground biomass of the three dominant species in September under different seasonal grazing treatments.In August,the 0-5cm underground biomass of seasonal grazing and enclosed plots was significantly higher than that of other soil layers（P<0.05）.The 5-10cm soil layer underground biomass of the enclosed plot was significantly higher than that of the autumn grazing plot（P<0.05）.The 15-20cm soil layer underground biomass of the autumn grazing plot was significantly higher than that of the summer and enclosed plots（P<0.05）.3.Different seasonal grazing treatments have no significant effect on theδ¹⁸O value of soil water,while the interaction between sampling time and soil depth,the interaction between sampling time and seasonal grazing,and the interaction between sampling time and soil depth have extremely significant effects on soil waterδ¹⁸O（P<0.01）.Theδ¹⁸O value of 0-20cm soil water in different seasonal grazing plots fluctuates greatly.As the soil depth increases,the fluctuation of theδ¹⁸O value in the soil profile gradually decreases.Sampling time had a very significant effect on theδ¹⁸O values of three Stipa grandis,Leymus chinensis and Cryptospermum scabra（P<0.01）.Comparing the slopes of the fitting equations of hydrogen and oxygen isotope values between plants and soil water,it is found that plants in spring grazing and enclosed plots are sensitive to changes in soil moisture,while plants in grazing plots in summer and autumn respond relatively slowly to changes in soil moisture.4.In the absence of precipitation,the different seasonal grazing plots of Cleistogenes squarrosa,Stipa grandis and Leymus chinensis mainly use 0-10cm soil water,and the water source does not fluctuate significantly with seasonal changes.5.The three dominant plants in the seasonal grazing plots after the summer moderate rain event and the light rain event mainly absorb0-10cm soil water;after the rain,the contribution rate of water use in the0-10cm soil layer of Stipa grandis,Leymus chinensis and Cleistogenes squarrosa There is improvement.6.Seasonal grazing treatment had no significant effect on the instantaneous water use efficiency（WUE_t）of the three dominant plant species;the sampling time had a very significant effect on the WUE_t of Leymus chinensis and Cleistogenes squarrosa scabra（P<0.01）.7.Seasonal grazing has a very significant impact on the long-term water use efficiency（WUE_L）of Stipa grandis and Cleistogenes squarrosa（P<0.01）,and has no significant impact on the WUE_L of Leymus chinensis;The WUE_Lof Stipa has a significant impact（P<0.05）,and the sampling time has a very significant impact on the WUE_L of Cleistogenes squarrosa serrata（P<0.01）.