| Ningxia desert steppe is one of the areas where desertification occurs seriously in China.In order to restore vegetation and curb the desertification trend of grassland,large-scale plantation of artificial shrubs has been carried out since 1980s.Caragana korshinskii and Salix psammophila are typical artificial sand-fixing forests in Ningxia desert steppe.However,with the decline of branches and leaves,weakening of growth potential and occurrence of pests and diseases in early introduced plantations,it is urgent to study the relationship between growth characteristics of artificial shrub forests and soil moisture in desert steppe.Taking C.plantation and S.in desert steppe of Yanchi County in Ningxia as the research object,the sample plots were set as C.mixed forest,C.pure forest and S.pure forest according to the characteristics of vegetation growth.The soil moisture content,soil physical and chemical properties,growth and development of forest and water physiological characteristics of different shrub forests were monitored regularly,and the growth and physiological characteristics of forest in different shrub forests were analyzed.The relationship between soil water environment provides theoretical and technical basis for vegetation construction in this area.The results show that:（1）The characteristics of soil moisture change of different artificial shrub forests in desert steppe can be divided into five periods in 2018,and three functional levels according to the characteristics of vertical change.The soil moisture content of C.pure forest was higher than that of C.mixed forest and S.pure forest.Soil water content of artificial shrub forests with different groundwater depth in desert steppe is in good agreement with seasonal distribution of precipitation.（2）The content of soil physical and chemical properties in mixed forest sample plot was higher than that in pure forest sample plot.Soil particle size composition showed fine clay in 0-10 cm soil layer,and coarse clay was significantly larger than other layers.Very fine sand in 10-80 cm soil layer was significantly larger than surface soil（0-10 cm）and deep soil（80-100 cm）.Fine clay and coarse clay in pure forest sample land were significantly higher than that in mixed forest sample land.S.pure forest was significantly higher than that of C.pure forest and C.mixed forest.With the increase of soil depth,soil conductivity and total carbon decreased in 0-40 cm soil layer and increased in 40-100 cm soil layer.Soil pH of Caragana Salix mixed forest decreased in 0-40 cm soil layer,and increased in 40-100 cm soil layer.Soil pH of Salix and C.pure forest increased with the increase of soil depth.（3）The plant height,crown width,basal diameter and branch number of C.pure forest and S.pure forest and their mixed forests showed sustained growth in growth.June and September were the months when the growth of different artificial shrubs was significant in desert steppe.The net photosynthetic rate of mixed forest sample plot was higher than that of pure forest,and that of C.forest was higher than that of S.forest.The transpiration rate and stomatal conductance were the same,and reached the peak in August.The change trend of intercellular CO2 concentration and net photosynthesis was inconsistent.The net photosynthetic rate and water use efficiency of C.and S.were higher.（4）Malondialdehyde content of the two plants fluctuated and decreased.C.pure forest was higher than C.mixed forest,and S.mixed forest was higher than S.pure forest.In different plots,the soluble sugar content in the leaves of both plants was increasing,and the soluble sugar content in S.was higher than that in C..Malondialdehyde content in leaves fluctuated during growth,and the pure C.forest was higher than the mixed C.forest,and the mixed Salix forest was higher than the pure S.forest.Peroxidase activity of C.and S.reached its maximum in August and September respectively.Through comprehensive comparative study,it is found that osmotic regulation is affected by both environmental factors and individual development level of plants.（5）Soil water content of different shrub plantations in desert steppe was positively correlated with total nitrogen,bulk density and very fine sand grains,and negatively correlated with C/N ratio.The growth characteristics of C.and S.mixed forests were significantly correlated with soil water content in 0-80 cm soil layer,and the growth indexes of C.and S.pure forests were significantly correlated with soil water content in 0-100 cm soil layer.Soil water content in 40-60 cm soil layer was significantly correlated,and net photosynthetic rate,stomatal conductance,intercellular CO2 concentration,water use efficiency,chlorophyll and other indicators were significantly correlated with soil water.Soil water content of shrub forest has significant effects on soil photosynthetic physiological indices（total nitrogen,bulk density,ultra-fine sand,C/N ratio）,net photosynthetic rate,stomatal conductance,intercellular CO2 concentration,water use efficiency)and stress-resistant physiological indices（chlorophyll）. |
