Effects of water stress on Haloxylon ammodendron seedlings in the desert region of Heihe inland river watershed, Gansu Province, China

The water relation and leaf gas exchange of saxoul (Haloxylon Ammodendron Bge, a C4 shrub) seedlings were studied under water stress in 2001. Saxoul seedlings maintained high transpiration when the soil moisture was above 11%. The seedlings were able to take up water from soil with above 6 % soil water content, which was the threshold level of soil moisture for seedlings. The relationship between transpiration and potential evaporation was linear for well-watered seedlings. The decrease of soil water availability led to different degrees of down-regulation of stomatal conductance, leaf transpiration and net CO2 assimilation rate. The stomata played a relatively small part in determining the net CO2 assimilation rate for the same seedling. The relationship between net CO2 assimilation rate and transpiration was linear diurnally, and reduction scale of leaf transpiration was much bigger than that of net CO2 assimilation rate by waters tress treatments, therefore intrinsic water-use-efficiency increased. High evaporative demand increased the leaf transpiration but inhibited net CO2 assimilation rate.Because of the effect of VPD on transpiration in this region, the transpiration of well-watered and mild water stress seedlings becomes responsive to change in stomatal conductance over a wider range.

Effects of water stress on<Emphasis Type="Italic">Haloxylon ammodendron</Emphasis> seedlings in the desert region of Heihe inland river watershed,Gansu Province,China

The water relation and leaf gas exchange of saxoul (Haloxylon Ammodendron Bge, a C₄ shrub) seedlings were studied under water stress in 2001. Saxoul seedlings maintained high transpiration when the soil moisture was above 11%. The seedlings were able to take up water from soil with above 6% soil water content, which was the threshold level of soil moisture for seedlings. The relationship between transpiration and potential evaporation was linear for well-watered seedlings. The decrease of soil water availability led to different degrees of down-regulation of stomatal conductance, leaf transpiration and net CO₂ assimilation rate. The stomata played a relatively small part in determining the net CO₂ assimilation rate for the same seedling. The relationship between net CO₂ assimilation rate and transpiration was linear diurnally, and reduction scale of leaf transpiration was much bigger than that of net CO₂ assimilation rate by waters tress treatments, therefore intrinsic water-use-efficiency increased. High evaporative demand increased the leaf transpiration but inhibited net CO₂ assimilation rate. Because of the effect of VPD on transpiration in this region, the transpiration of well-watered and mild water stress seedlings becomes responsive to change in stomatal conductance over a wider range. Foundation item: The research was supported by Innovation Research Project of Chinese Academy of Sciences (KZCX1-10-03), National Natural Sciences Foundation of China (90102003), and West Development Technology Project (2001BA901A42). Biography: LIU Fa-min (1963-), male, Ph. Doctor of Cold and Arid Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou 730000, Gansu, P. R. China. Responsible editor: Song Funan