Transpiration Characteristics Of Three Desert Shrubs Under Different Habitats On The Southern Margin Of The Junggar Basin

The desert vegetation growing in the southern edge of Junggar Basin mainly depends on precipitation and groundwater. it is degenerating due to over-exploitation and irrational usage of water resources. The purpose of this research is for deeply understanding the water physiological characteristics of desert plants and its mechanism of water consumption. There are great significance for the water allocation and the vegetation restoration of degeneration desert ecosystem.This study focuses on the three dominant species shrubs:Haloxylon Bunge, Tamarix elongata and Calligonum arborescens growing in the southern edge of Junggar Basin. The experiments was carried out in the National Fukang Desert Ecosystem Field Sciences Observation and Research Station, by means of thermal diffusion sap flow measure system, Li-6400 photosynthesis systems and so on. The sapflow of 3 desert shrubs in different habitats and its relationship with meteorological factors and soil water were studied. The main results are as follows.(1) The sapflow velocity at different depths of xylem of Haloxylon ammodendron growing in the Gurbantunggut Desert have consistent diurnal variation procedure. The peak value of sapflow velocity at 10mm in xylem (VTDP10= 15.73 cm·hr-1) is higher than that at 30mm (VTDP30= 10.545 cm·hr-1). The variance of diurnal average sapflow velocity in different depths has no significant differences, and the average sapflow velocity has significant differences. The sapflow velocity has a positive correlation with solar radiation, air temperature and soil temperature, and negative correlation with relative air humidity and vapor pressure. The correlation coefficient of solar radiation is higher than other parameters. The effect of wind speed on the sapflow velocity during the bloom is larger than other growing periods. The begining and falling time of sapflow velocity on the north and south of trunk are consistent. The sapflow velocity on the north was generally higher than that on the south., the time appearing the peak of sapflow velocity on the northern trunk is delayed 30 min Comparing with the southern trunk. The start-up time of sapflow velocity on the northern trunk is earlier 30 min than the southern trunk in the later growing period. The diurnal process showed single-peak. The variations of daily average sap flow velocity on both directions had no significant difference, and the same for the daily average sapflow velocity. The sapflow velocities of Haloxylon ammodendron growing in different position of the sand dune are different seriously. The sapflow velocity are 2.51 L·d-1,2.5 L·d-1 and 1.78 L·d-1 at the foot, nose and top respectively. Drought resistance of Haloxylon persicum is better than that of Haloxylon ammodendron.(2) The mean sapflow velocity and diurnal cumulative sapflow flux of the three artificial planting desert shrubs are:Haloxylon ammodendron> Tamarix elongata> Calligonum arborescens. The highest sapflow velocity of artificial planting Haloxylon ammodendron is 33.44 cm·hr-1. The curve of daily process of sapflow velocity is single-peak style. The more abundant water, the more obvious single peak. The mean sapflow velocity and diurnal cumulative sap flow flux at 30mm depth of xylem are respectively 3.16 cm·hr-1 and 3.01 L·d-1 during the observation period. The sapflow velocity are significantly correlated with air temperature, and significantly negative correlated with relative air humidity and vapor pressure. The highest sapflow velocity for artificial planting Tamarix elongata was 46.60 cm-hr-1. The curve of daily process of sapflow velocity is single-peak style, and there was sapflow at night. The mean sapflow velocity and diurnal cumulative sap flow flux at 30mm depth of xylem are respectively 2.67 cm·hr-1 and 2.47 L·d-1. The sapflow velocity are significantly correlated with air temperature and solar radiation, and negative correlated with relative air humidity. The correlation coefficient are 0.835,0.656 and -0.631 respectively. The highest sapflow velocity for artificial planting Calligonum arborescens was 48.90 cm·hr-1. The mean sapflow velocity and diurnal cumulative sap flow flux are respectively 0.81 cm·hr-1 and 0.46 L·d-1. The curve of daily sapflow velocity is single-peak style. The highest sapflow velocity is on sunny day, then the light day, cloudy day, and rainy day in proper order. The sapflow velocity are significantly correlated with air temperature and solar radiation, negative correlated with relative air humidity significantly.(3) For the sand dune growing the experimental Haloxylon ammodendron in the Gurbantunggut Desert, the volumetric soil moisture content in 2 m layer increased gradually from the top to the foot. The amplitude of soil moisture content decreased gradually from the nose, the base and to the top of sand dune. The soil moisture in 40 cm below the surface varies most, followed by 70 cm to 160 cm layer, and other layer varied relatively smaller. In the layer with biggest amplitude, The lower soil moisture content, the better relationship between diurnal cumulative sapflow flux and the soil moisture at root zone. The irrigation could influnce the Haloxylon ammodendron, Tamarix elongata and Calligonum arborescens till 110cm,130cm and 160cm below the surface respectively.(4) The start-up time of sapflow velocity of natural Haloxylon ammodendron at the first day after the rainfall is postponed about two hours than that before the rainfall. The time happened the sapflow velocity peak is postponed one hour than that before the rainfall. The longer time after the rainfall, the closer the starting time of sapflow velocity and the time appearing sapflow peak to that before the rainfall. The scarcer of soil moisture, the shorter time appearing the sapflow peak postponed than that before the rainfall. The time appearing the sapflow velocity peak of artificial Haloxylon ammodendron at the first day after the rainfall is delayed only 10 minutes than that before the rainfall. The rainfall response for artificial planting Haloxylon ammodendron is less sensitive than the natural Haloxylon ammodendron.