Research on Leaf Transpiration Response to Soil Water Stress of Caragana korshinskii Kom. in Hedong Sandy Land of Ningxia

Caragana korshinskii Kom., a type of psammophilic shrub growing in Hedong sandy land of Ningxia was transplanted in pots in a greenhouse and treated with progressive water stress. The leaf transpiration characteristics under different soil water condition were studied to reveal the response mechanism of plant leaf transpiration to main environmental factors. It is expected that the study will provide the scientific basis for optimizing forest structure allocation of regional vegetation restoration and reconstruction in arid region. It was shown that:(1) The transpiration rate of C. korshinskii Kom. under the adequate soil water supply is exactly 3.43 times than that in severe water stress. The transpiration peak moved forward while increasing of soil water stress, and the daily transpiration rate varied in a double-peak curve under the severe drought stress. There was a linear correlation between leaf transpiration(Tr) and stomatal conductance, both were the same dynamics under different soil water condition.(2) As the soil water content reduction, the transpiration rate of C. korshinskii Kom., after reaching its peak figure, will slowly decrease. The critical value of soil water content(SWC) was 15.78%(that was 74.1% of field moisture capacity).(3) Light response curves of leaf transpiration under low photosynthetically available radiation(PAR) in different SWC made little different. The leaf transpirations under low solar radiation were up with linear while increasing of PAR. However, the start-up speeds of Tr were decrease with soil water content reduction. Under the soil water stress(SWC≤40% of field moisture capacity), any further increase in PAR(≥1 000 μmol·m-2·s-1), however, was not helpful to improve Tr. Meanwhile, it was arguable that increase the light radiation intensity led to decreased transpiration rate under the severe soil water stress. And(4) after analysis of partial correlations, the PAR was the major factor influencing changes of Tr under the adequate soil water supply, contributing 54.4% of the variation Tr. But with the decline in soil moisture, the sensitivity of stomata decreased to PAR. The vapour pressure deficit between air and leaf became the dominant factor in regulating transpiration process of C. korshinskii Kom..