| Grassland is an important part of terrestrial ecosystem,which has multiple ecosystem functions such as soil and water conservation,water conservation and climate regulation.Water resource is the restrictive factor of grassland ecosystem,which plays an important role in green development and sustainable utilization of grassland.The grassland area is ecologically fragile and easily disturbed by human activities.Rotational grazing in four seasons is the most traditional way of grazing and utilization in grassland ecosystem,which has certain effects on the characteristics of grassland vegetation and soil physical and chemical properties,but its effects on the characteristics of ecological water consumption and water use efficiency of grassland ecosystem are not clear.Therefore,this study took Stipa grandis community in typical steppe of Inner Mongolia as the research subject,and set up spring,summer,autumn and winter grazing treatment and enclosure and prohibition（control group）control experiment.In the growth season of 2020 and 2021（From May to August）,small lysimeter method,gas exchange method,sealing method and other experimental methods were used.Determination of different seasonal grazing community evapotranspiration water consumption and transpiration accounts for the proportion of evapotranspiration,combined with the feature of meteorological factors,soil moisture and community biomass investigation,systematic analysis of different season grazing on the influence of water use characteristics of Stipa grandis community,in order to understand the effect of seasonal grazing treatments on Stipa grandis from the perspective of water use and provide theoretical basis for formulating rational grazing management measures.The main results are as follows:（1）Two years’ observation showed that grazing in autumn significantly reduced the above-ground biomass in most months of the growing season compared with enclosure and prohibition,while grazing in spring,summer and winter had no significant effect on above-ground biomass in most months.The four seasonal grazing treatments had no significant effect on the underground biomass of 0-30 cm,0-10 cm and 20-30 cm.In 2021,the underground biomass of 10-20 cm under winter grazing treatment was significantly higher than that under enclosure and forbidden grazing treatment and spring grazing treatment,but there was no significant difference among different seasonal grazing treatments in 2020.（2）The grazing treatments had no significant effect on soil water content and soil water storage in 0-10 cm,10-20 cm,20-30 cm and 30-50 cm soil layers in most months of the growing season.Soil moisture content of each soil layer was positively correlated with above-ground biomass and evapotranspiration.Soil moisture content in surface layer（0-10cm）was significantly positively correlated with evaporation rate,while soil moisture content in other layers was significantly positively correlated with precipitation.（3）Two years of observation showed that grazing in autumn significantly reduced the evapotranspiration during the growing season of Stipa grandis community,grazing in summer had no significant effect on the evapotranspiration during the growing season of Stipa grandis,and grazing in spring and winter significantly reduced the evapotranspiration during the growing season of 2021,but had no significant effect on the evapotranspiration during the growing season of2020.Autumn grazing significantly reduced the monthly evapotranspiration of the community in most months of the growing season,while the other three seasons grazing had no significant effect on the monthly evapotranspiration of the community in most months of the growing season.The evapotranspiration of Stipa grandis community was significantly correlated with the total amount of soil water storage in0-50 cm soil layer and soil moisture content of each layer.In the growing season,evapotranspiration of Stipa grandis community was dominated by vegetation transpiration under grazing in different seasons,and vegetation transpiration accounted for 53%-96% of evapotranspiration.The transpiration rate of Stipa grandis community was significantly correlated with precipitation,aboveground biomass and total soil water storage in 0-50 cm.（4）Autumn grazing significantly reduced the total ecological water consumption in the growing season of Stipa grandis community,while summer and winter grazing had no significant effect on the total ecological water consumption in the growing season of Stipa grandis community,while spring grazing significantly reduced the total ecological water consumption in the growing season of 2021 community,but had no significant effect on the total ecological water consumption in the growing season of 2020 community.In most months of growing season,grazing in four seasons had no significant effect on monthly ecological water consumption.Ecological water consumption is affected by precipitation,aboveground biomass,evapotranspiration,soil water storage and soil moisture content.（5）Autumn grazing significantly reduced evapotranspiration water use efficiency,transpiration water use efficiency and ecological water use efficiency.Spring grazing significantly increased evapotranspiration water use efficiency,but had no significant effect on evapotranspiration water use efficiency and ecological water use efficiency.Grazing in summer and winter had no significant effect on evapotranspiration water use efficiency,but significantly reduced evapotranspiration water use efficiency and ecological water use efficiency in 2020,and had no significant effect on evapotranspiration water use efficiency and ecological water use efficiency in 2021.In conclusion,the above-ground biomass,evapotranspiration and water use efficiency of the community were significantly lowest under autumn grazing treatment,and the negative effects on the water cycle of the grassland ecosystem were the greatest. |
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