| As a global problem,desertification has seriously affected the sustainable development of Northwest,Northeast and North China.Therefore,the study of hydrology and water resources is a key and hot issue in desert ecosystem,and soil water is playing a key role in this issue.Driven by soil water,the succession of Artemisia Ordosica community in Mu Us sandy land undergoes a cyclic process:bare sandy land shifting sandy land(pioneer species stage)?semi-fixed sandy land(sparse stage)?fixed sandy land?fixed sandy land degradation stage?bare sandy land(or mobile sandy land).Previous studies focused on surface soil water content and shallow soil infiltration under simulated rainfall conditions,but they lacked real-time,long-term and continuous monitoring of soil water.Based on the existing research,this study used automatic monitoring system to monitor the precipitation and soil water in the study area continuously and quantitatively.Field investigation and field measurement were carried out.Combined with the root distribution of dominant species in the area,different types of sandy land(fixed sandy land,semi-fixed sandy land and shifting sandy land)in the study area were systematically analyzed.Distribution and dynamics of soil water in fixed sandy land and mobile sandy land,the response of soil water in different sandy land to natural rainfall,the factors affecting soil water change,the difference of rainfall recharge to soil water in different sandy land,the relationship of water balance and the proportion of soil water transformation in different sandy land were estimated and explored.Discuss the vegetation stability of sand consolidation and the vegetation carrying capacity of soil water.This study is helpful to reveal the characteristics of water change and water balance mechanism under rainfall and drought conditions.It has important theoretical and practical significance for further understanding the succession of vegetation communities in Maowusu sandy land,and can provide scientific basis for rational allocation of vegetation,vegetation restoration and reconstruction in arid and semi-arid sandy areasCompared with the traditional fixed-time and fixed-point soil moisture monitoring system,EC-5 soil moisture monitoring system,which is the latest monitoring method,can be used to monitor soil moisture for a long time and on a large scale,which ensures the quantity and continuity of data and better reflects soil moisture dynamics,precipitation infiltration and soil water balance.Condition.Compared with the traditional soil moisture dynamic analysis,the study period was divided into different periods by the standardized precipitation index method.In each period,the classical statistics and geostatistics were used to analyze the internal relationship between the spatial and temporal variability of soil moisture,and the main environmental factors were pre-sorted through RDA analysis.The factors affecting the spatial and temporal dynamics of soil moisture in different periods were analyzed.Then the contribution of the main controlling factors to soil moisture change was studied by quantitative separation of environmental factors The main conclusions of this study are as follows:(1)2014 is a wet year(moderate wet year),2015 is a water deficit year(moderate drought year),2016 and 2017 are normal years.There are significant differences in precipitation and effective precipitation times under different precipitation years.The precipitation times and precipitation amount in the growing season account for 87%or more of the total precipitation in the whole year,especially in July-September,which accounts for more than 80%of the total precipitation in the whole growing season.Rainfall intensity and frequency are at a low level in the study area.The occurrence frequency of rainfall intensity less than 2.5 mm/h is more than 80%,only about 1%of the rainfall intensity is more than 15 mm/h.The average precipitation interval in growing season is mainly 48-120 hours.(2)With the increase of vegetation coverage,the content of soil silt increased,soil structure became stable,soil water holding capacity and soil organic matter content gradually increased,which improved the ability of soil to retain water,fertilizer and wind erosion.The distribution trend of underground biomass in different plots was fixed sandy land>semi-fixed sandy land>shifting sandy land,and there were significant differences among them.Most root biomass was concentrated in 0-40 cm soil layer,and the root biomass decreased exponentially with the increase of soil depth.In the three types of plots,with the increase of vegetation coverage,the proportion of fine roots increased gradually,while the proportion of coarse roots and medium roots decreased gradually.(3)The change of soil water content is mainly affected by precipitation,root distribution of vegetation and soil physical properties.The seasonal dynamics of soil moisture in 0-120 cm layer of three types of plots can be roughly divided into three periods:1.From November to February of next year,the soil moisture content increased steadily,and maintained between 4%and 7%.(2)From March to July,soil water content increased significantly at first,but decreased slowly from May,and the minimum value was generally below 4%.(3)From August to October,soil water content increased significantly on the whole,and with the precipitation occurred many peaks.After September,precipitation decreases gradually and soil moisture decreases until the soil freezes.Soil moisture generally varies linearly from May to August and from August to October,but the slope and intercept of linear regression equation have no fixed law.The seasonal variation of soil moisture in fixed and semi-fixed sandy land is basically similar to that in mobile sandy land,that is,the change of soil moisture is synchronized with that in rainy season.But the main difference between them and mobile sandy land is the distribution of soil water content in May-July.Precipitation in August and September resulted in two peaks of soil water content in mobile sandy land and semi-fixed sandy land,while soil water content in 160 cm and 200 cm layers of fixed sandy land remained unaffected by excessive precipitation.Value.(4)The spatial distribution of soil water content is mainly divided into three layers:0-10cm layer has the greatest change in soil water content,which is the dramatic change layer;10-120cm layer is the active layer of soil water content,which is mainly affected by moderate rain,heavy rain,rainstorm and continuous precipitation;120-200cm layer has relatively stable change in soil water content,which is soil water content.Soil water stable layer has little effect on precipitation,temperature and plant root distribution,and is generally only affected by heavy rainfall.The change of soil water content with soil depth in fixed sandy land has the characteristics of "slow rise and fast decline".The slope of the regression equation of soil water content with soil depth in 10-40 cm layer is significantly lower than that in semi-fixed Sandland and mobile Sandland in 10-60 cm,while the regression equation of soil water content with soil depth in 40-200 cm layer is significantly lower than that in semi-fixed Sandland and mobile Sandland in 10-60 cm.The slope of the course is significantly smaller than that of semi-fixed sand land and mobile sand land,but there is no fixed law between the slope of semi-fixed sand land and mobile sand land.The intercept of regression equation is positively correlated with precipitation.The intercept of regression equation in the same soil layer between flood year,deficit year and peacetime year in the study period shows that the intercept of abundant year is significantly larger than that of deficit year and peacetime year,the intercept of deficit year is significantly smaller than that of flood year and peacetime year,and the intercept of regression equation in the same soil layer between flood year,deficit year and peacetime year.There was no significant difference between them.(5)From 2014 to 2017,after each precipitation event,the soil water content of 0-60 cm layer in each plot will change greatly,and the correlation with the soil water content before precipitation is significant and extremely significant.With the increase of vegetation coverage,the spatial heterogeneity caused by randomness decreases and the continuity of spatial distribution of variables increases.After each precipitation,the maximum value of surface soil water content is significantly higher than that of deep soil The maximum value of soil water content after the second precipitation is significantly higher than that after the first precipitation.In terms of time,there is a significant difference in the time required for soil water content to reach the maximum value after two precipitations,showing the rule of mobile sandy land<semi-fixed sandy land<fixed sandy land.Initial soil water content has a significant effect on infiltration and redistribution,which makes a significant difference between the migration rate of wetting front and the maximum soil water content after rain.The establishment of sand-fixing vegetation increases the temporal stability of soil moisture,reduces the spatial heterogeneity of soil moisture,and has a significant impact on the distribution and dynamics of soil moisture,precipitation infiltration and soil water balance in the study area.Soil water storage will not decrease in the year of high water and peaceful water,and the recharge of precipitation to soil water can basically meet the evapotranspiration demand.However,under drought conditions and water deficit years,the soil water storage of fixed sandy land appears deficiency.In order to avoid the degradation of Artemisia ordosica community in fixed sandy land,this study suggested that the maximum vegetation coverage should not exceed 70%in vegetation restoration.The two chamber model of the chamber analysis method is used to simulate the infiltration of precipitation.After the preliminary verification of the model,the parameters are modified.The results show that the parameters of the model after the parameter modification meet the set value range,the goodness of fit meets the statistical requirements,and the modified model can better reflect the infiltration of different precipitation,different rainfall intensity and different areas.According to the different range of parameters in the improved model,it can express the relationship between plant and soil water under different rainfall conditions and different time periods.After applying the precipitation data of 2015-2017 to verify the model,it is found that the applicability of the modified model is good,and the model classification is also very reasonable(6)13 environmental factors(precipitation,rainfall intensity,precipitation interval,soil initial water content before precipitation,root biomass,soil bulk density,soil particle size,soil temperature,wind force and wind speed,solar radiation,soil organic matter content and air)affecting soil water storage in different plots,time periods and soil layers Humidity)can explain more than 85%of the variation of soil water storage,and can provide more than 90%of the relative contribution rate,and the top two environmental factors can provide more than 80%of the relative contribution rate.However,only precipitation,precipitation interval,rainfall intensity,root biomass and initial soil water content can significantly affect soil water content;soil bulk density and soil particle size have little contribution to soil water storage change,and moisture,temperature,soil organic matter,wind and wind speed have little effect on soil moisture in three types of sample plots.The effect of soil water storage is almost negligible.In addition to initial soil moisture,the most important factor affecting soil moisture in fixed sandy land is vegetation coverage(root biomass).The most important factor affecting soil moisture in mobile sandy land is precipitation pattern(including precipitation,rainfall intensity and precipitation interval).Soil moisture balance in semi-fixed sandy land is affected by vegetation and precipitation.Double effects.After path analysis and redundancy analysis of soil water storage,the variation of soil moisture in different layers can be well predicted by multiple regression equation. |
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