河西走廊不同生态类型芦苇的气体交换特点的研究

STUDY ON GAS EXCHANGE CHARACTERISTICS OF PHRAGMITES COMMUNIS TRIN. IN DIFFERENT ECOTYPES OF DRY DESERT OF THE HEXI CORRIDOR

在自然条件下对生长在甘肃省河西走廊干旱荒漠地区的水生、沙生和盐生芦苇叶子气体交换特点进行了比较研究。结果表明,水生芦苇具有典型的单峰净光合速率日变化曲线,而沙生和盐生芦苇则具有非典型的双峰净光合速率日变化曲线。水生芦苇的光合速率终日均大于沙生和盐生芦苇,而后二者的光合速率基本相似。水生芦苇气孔导度有明显的日变化,其变化趋势与净光合速率日变化趋势一致,但沙生和盐生芦苇的气孔导度日变化幅度小,且终日低下,而这与群落冠层大气相对湿度密切相关。三个不同生态类型芦苇在12:00—20:00时光合速率下降的决定因素是叶肉细胞光合活性,而在4:00—12:00时,三者净光合速率的下降则主要是由于气孔导度降低之故。

The gas exchange characteristics of leaves of the aquatic, arenaceous and halophilous Phragmites communis Trln. Growing in dry desert region of the Hexi Corridor, Gansu province, were studied under natural conditions by using a protable Li-6000 gas analysis system. Daily time courses of gas exchange, air ternperature(Tα), photon flux density (PFD) and air relative humudity(RH) were monitored in hot, sunny days. Significant differences in gas exchange characteristics were found between the three differente ecoty-pes of Phragmites communis Trin., with aquatic phragmites having higher net photosynthesis rates(PB) and intercellular CO2 concentrations(Ci). In particular, stomatal conductance(Gs) was higher in aquatic phragmites than in arenaceous and halophilous phragmites, and both the latters had very low G, throughout a day. The significant differences in daily time courses of stomatal conductance between the three defferent ecotypes of phragmites are resulted from significant defferences in air relative humidity in canopies of the various ecotypic phragmites without corresponding to incident radiation and air temperature in canopies. On the basis of analysis of stomatal limitation of photosynthesis using two criteria (intercellular CO2 concentration and stomatal limiting value) suggested by Farquhar and Sharkey(1982), it is concluded that although the predominant limiting factor of photosythe-sis in arenaceous and haliphilous phragmites is stomatal conductance which may represent adaptation to low air relative humidity in their habitats, the significant differences in gas exchange characteristics of the three different ecotypes of phragmites cannot rule out the differences in the photosynthe-tic capacity of mesophyll cells between aquatic, arenaceous and halophilous Phragmites communis Trin.