Study On The Relationship Between Soil Moisture Dynamics And Leaf Area In Semi-arid Loess Region

The aim of the thesis is to explore the dynamics of soil moisture and the adaptation and strategies of plants to the moisture,by the study of soil moisture variations of eight typical types vegetation types,of leaf area and soil moisture coupling,in order to provide evidence and insights for the sustainability of vegetation restoration,soil water conservation and ecological environment construction.The thesis studied on the whole area of Longtan river basin,setting up locations according to slope angle,direction and position.Soil moisture of 0-1.8 m and 0-5 m depth was measured based on TDR(Trime-FM)and drying method,for better accuracy.Leaf area was measured by leaf planimeter or scanner,and by LAI-2200C(Li-cor,USA)in order to obtain index of leaf areas.Data was processed and illustrated by Origin 9.1 and Excel.The results showed:(1)The dynamic monitoring of soil moisture in shallow soil and the seasonal sampling of deep soil moisture showed that the soil moisture of different vegetation types had the characteristics of high volatility in the shallow layer.At the same time,due to rainfall,vegetation transpiration and soil evaporation,the function of soil moisture in 1 m appeared a relatively obvious turning point,where the depth of 1 m below the soil moisture content would be stabilized with the increase of the depth of the seasonal change while moisture content would have obvious rise.In general,the soil moisture content of all kinds of soil showed a decrease from May to August,yet increase in August to October.The soil moisture content of shallow soil was relatively varied due to seasonal effect,while the deep soil moisture content was relatively stable.Rainfall could have a great influence on the change of soil moisture content in shallow soil.However,the change of soil moisture content in deep soil was more likely to be influenced by vegetation.Rainfall would supplement the soil water in the area,but not in artificial vegetation.Therefore,the selection of vegetation types is also critical to the protection and restoration of soil moisture in the region.(2)The soil moisture content of farmland,natural grassland and abandoned farmland should be significantly better than artificial vegetation(alfalfa,caragana,peaches,oil pine,and side cyb).Especially,for deep soil moisture,the deep soil moisture of artificial vegetation was much lower than of abandoned farmland,natural grassland and farmland,which indicated that artificial vegetation had a significant impact on soil moisture.This indicated that deep soil water could provide limited water for introduced-vegetation under normal precipitation.(3)For evergreens like Pinus tabulaeformis and arborvitae,leaf area index of the overall change in its growing season was not significant.Pinus tabulaeformis and arborvitae sample area had soil moisture in severe deficit condition,where the effect of rainfall on soil moisture complement were not obvious.Armeniaca sibirica,wild peach,caragana korshinskii,poplar,lai and esparto grass vegetation were greatly influenced by rainfall and leaf area index in growing season increased first and then decreased.In raining season,alfalfa was affected by local farming related,showing increasing trend of leaf area index.Overall,semiarid loess hilly-gully region vegetation the leaf area increased where the rainy season gave rise to the fastest-growing.Adaptation of leaf area change was affected by factors such as vegetation types and the external environment.(4)The effect of soil moisture on vegetation growth displayed a certain time delay effect that the soil moisture status of the previous year has a significant effect on vegetation growth in the next year.From April to June,water loss had the most significant influence on next year's arbor vegetation growth,while for herbs early hydrating soil moisture condition from June to September was the major player.Vegetation growth of soil moisture is mainly concentrated in the 0.4-1 m soil depth,whereas 0-0.4 m shallow soil moisture was affected by evaporation and vegetation transpiration therefore not for plant absorption.