Studies On The Characteristics Of Water Absorption, Transpiration Water Consumption And Eco-Hydrological Effects Of Caragana Intermedia

In Arid and Semi-arid Regions, water becomes the main factor to constrain plant growth. So to calculate accuvelocityly the absorption and water deprivation of plant and its eco-hydrological effects has the guiding significance to the rational planting and scientific management of plant. In this research, we choose Caragana intermedia as the object, which is an excellent wind-breaking and sand-fixing shrub species widely distributed in the Desert-steppe of Mongolian Plateau and the typical steppe region of northern Loess Plateau. On the basis of predecessors' work and the adoption of advanced Granier's thermal dissipation probe method and stable isotope technique, we have a detailed analysis on Caragana intermedia in sand soil and in loess about the water absorption, characteristics of stem sap flow, transpiration water consumption, community characteristics and water utilization. While clarifying the drought resistance mechanism of Caragana intermedia, we have an analysis on the water balance condition of Caragana intermedia community in the Hunhe river basin. On the basis of general investigation, we choose Maowusu sandlot and the Hunhe river basin in the hilly area of Loess Plateau as the research area. The results are as follows:1. Water absorption characteristic of Caragana intermedia1) The root system of Caragana intermedia is quite plastic, which can help the plant to adapt to different water capacity in different ground substances. The characteristic of root morphology of Caragana intermedia in sand soil is as below: the rooting depth of main root is shallow; the branch roots and absorbing roots (diameter less than lmm) mainly distribute in 10-30cm soil layer, which account for 72.2% of the total amount of roots, and the branch roots mainly grow horizontally. The characteristic of root morphology of Caragana intermedia in sand loess is different:the main root takes root deep, and its diameter becomes smaller as it goes deeper; the number of branch roots and absorbing roots (diameter less than 1mm) decreases as the depths grows. The branch roots and absorbing roots mainly distribute in the 0-70 cm soil layer and the number of those in the 0-50 cm soil layer account for 91.7% of the total amount of roots.2) There is hydraulic lift phenomenon in Caragana intermedia, but it is the most important effect plant between 18:00 and 2:00 the next day. This phenomenon can not only satisfy its own needs for water, but also provide water for plants nearby, thus improving the competitive strength of Caragana intermedia and other nearby plants without hydraulic lift. Experiments show that the amount of water lifted by young plant of Caragana intermedia is 1.33g per plant per day.3) There are different ways of water absorption for Caragana intermedia in two different ground substances. Caragana intermedia growing in sand loess can absorb water in deep soil with main root and also water in shallow layer of soil with its rich absorbing roots. Caragana intermedia in sand soil mainly makes use of water in the shallow surface and increases absorbing area by its branch roots that grow horizontally.2. Sap flow characteristics of Caragana intermedia1) The daily variation of sap flow velocity of Caragana intermedia is wide-peak curve, and there is no obvious phenomenon of "nap". It can be divided into four stages:rapid ascending period, stationary period, rapid descending period and nighttime period. The variation is mainly influenced by factors such as solar radiation, air temperature, vapor pressure deficit, relative air humidity, soil temperature and wind speed. Among these factors, relative air humidity has the obvious negative correlation with sap flow velocity, while all others have obvious positive correlation.2) The daily variation of sap flow velocity of Caragana intermedia does not keep pace with solar radiation, and vapor pressure deficit, but there is time-delay. The sap flow velocity variation of Caragana intermedia in sand soil is 60 minutes behind solar radiation and 90 minutes before vapor pressure deficit. The sap flow variation of Caragana intermedia in May and July in loess is 30 minutes behind solar radiation, and there is no time delay in September. In May and September, the vapor pressure deficit is 150 minutes behind the sap flow variation of Caragana intermedia, and the time delay in July is 120 minutes.3) There is a difference between sap flow velocity and sap flow capacity in Caragana intermedia. In May, the sap flow velocity (0.05kg·h-1), and the sap flow capacity (36.75kgH2O·strain-1) are the lowest, while that in July reach the highest in the grow season with the sap flow velocity (0.08kg·h-1) and the sap flow capacity (62.52kgH2O·strain-1). In August and September, the sap flow velocity and sap flow capacity begin to drop but still keep at a relatively high level. The seasonal sap flow velocity variation of Caragana intermedia has positive correlation with vapor pressure deficit, solar radiation, air temperature and wind speed while it has negative correlation with relative air humidity.4) There is nighttime water compensation in Caragana intermedia. Nighttime sap flow still exits in Caragana intermedia, but compared to daytime sap flow,the rate variation at night is slow, the curve is relatively smooth and the amount of sap flow is obviously lower. This is to compensate for the water deficit caused by strong transpiration during the day, and the nighttime sap flow rate in different months are different.5) The sap flow of Caragana intermedia varies in different weather conditions, and the environmental factors that affect the sap flow are different. But solar radiation is always the main environmental factor that affects the sap flow of Caragana intermedia.3. The transpiration water consumption characteristics of Caragana intermediaWhen calculating the transpiration water consumption by way of sap flow, it is necessary to get rid of the sap flow at night. The seasonal variation curve of transpiration of single Caragana intermedia is paracurve. The transpiration is the highest in July, and the lowest in May. In September, the transpiration still keeps at a high level, even though it has reached the later period of growth. Besides, the transpiration is different in different weather conditions, in which it is higher in clear days than in cloudy days.4. The transpiration water consumption of Caragana intermedia shrub and its eco-hydrological effects1) The transpiration of Caragana intermedia community is the highest in July. The transpiration of Caragana intermedia community in sand loess during the whole growth period reaches the lowest in May (19.53mm) and the highest in July (45.65mm). In September, the transpiration still keeps at a high level (27.6mm), even though it has reached the later period of growth. The seasonal variation curve of transpiration of Caragana intermedia is paracurve.2) There is a water balance in Caragana intermedia community. In an ideal state, there is a water surplus in July (middle period of growth); while there is a water deficit in varying degrees in May (early period of growth) and September (later period of growth). This explains that precipitation can not satisfy the water need of Caragana intermedia community, and the plant has to absorb water from the soil, which accelevelocitys the water deficit in the soil.3) The eco-hydrological effects of Caragana intermedia community.①There is a phenomenon of dry layer of soil every month in the Caragana intermedia community. The water content in the soil is below the point of wilting moisture most of the time. The soil is extremely lack of water.②There is an obvious difference in soil water content in and outside the Caragana intermedia community. The dry layer of soil is quite obvious in the Caragana intermedia community, but it is not the case outside the Caragana intermedia community.③Compared to other plant communities nearby, the water content in different layers of soil in the Caragana intermedia community is lower, and there is obvious dry layer of soil. The water content below 80cm is below the point of wilting moisture, and there is extreme lack of water in the soil, which means Caragana intermedia is more likely to cause dry layer of soil.④Compared to other plant communities, the soil reservoir in the Caragana intermedia community lacks the ability of the self-control, which means 88.53% of ability is permanently lost. The water exchange depth in the Caragana intermedia community is 80-100cm, below which the water can not exchange effectively and the problem of day layer of soil can not be solved.4) The water budget of Caragana intermedia community during growth period in the Hunhe River basin is as follows:if only depending on precipitation, there is a water surplus of 26.9mm in July, and there is a water deficit in varying degrees in May and September, which are 8.58mm and 2.8mm respectively.