Effect Of Water Input During Freeze-thaw Period On Soil Hydrothermal Dynamics In Typical Grassland Of Inner Mongolia

The typical grassland of Inner Mongolia is an important base of animal husbandry in China,and also an important ecological shelters for northern China.In recent years,due to climate drought,excessive utilization,the Inner Mongolia steppe have been seriously degraded,which affecting the water and thermal cycle in this region,and break the balance relationship between water-hermal cycle and the surface vegetation growth,resulting in a significant reduction of the grassland ecosystem function.Water is the major limiting factor for productivity and species composition in typical grasslands in Inner Mongolia.Soil water input during freezing and thawing period has an important impact on the water and thermal dynamic,nutrient circulation and vegetation growth in the whole year.However,the influence of the soil moisture changes during freezing and thawing period on the hydrothermal dynamics is rarely reported in Inner Mongolia grassland.In this study,we enclosed a field in typical grasslands in Inner Mongolia,the water was added during the freeze-thaw period,three moisture treatments were set up,1)Without adding water treatment(W0),2)Autumn water input before freezing(W1),3)Autumn water input before freezing in autumn + snow input before melting in spring(W2).The soil temperature and soil water content in five(0-100cm)layers were continuously monitored for each treatment in long-term.We analyzed the temperature and soil water dynamic changes in each soil layer under different water treatment.Combined with the meteorological data,the Hydrus-1D model was used to simulate the soil hydrothermal changes under different water treatments,and further verified the accuracy.The main study results are as follows:1.The water addition during the freeze-thaw period significantly increased the soil water content of the underlying(50-100cm)soil layer in the warming season of the next spring,up by57%-84%.2.During the freezing period,the addition of water delayed the freezing drop time of0-100 cm soil layer,and increased the amplitude of the freezing drop.During the melting period,the water addition during the freeze-thaw period advance the melting time of 30-70 cm soil layer,and improves the melting range of 30-100 cm soil layer.3.Water addition during the freeze-thaw period increased the coefficient of variation of the soil water content in the 30-100 cm soil layer,indicating a more drastic change in soil moisture in each layer.4.Water addition during the freeze-thaw period significantly increased the soil temperature and the minimum temperature during the freezing period in 0-100 cm each soil layer.5.The Hydrus-1D model is used to simulate the soil water content and soil temperature change under different water treatments,which shows that the model can better simulate the soil temperature change under different water treatments,and the simulation accuracy of the soil water content change is not high enough.The water addition during the freeze-thaw period can significantly improve the deep soil water content,delay the freezing time,advance the melting time,and increase the minimum soil temperature.Changes in these soil hydrothermal parameters may have a significant impact on vegetation growth and species change.