干旱区生态环境知识资源中心

To investigate the variations of anatomical and photosynthetic carbon metabolic characteristics within one species in response to increasing soil water stress, leaf anatomical characteristics, gas exchange and the activity of key enzymes in photosynthesis and photorespiration were compared in different ecotypes of Phragmites communis growing in an oasis-desert transitional zone (ODTZ) from swamp habitat (plot 1-3) via heavy salt meadow (plot 4-7) and light salt meadow habitat (plot 8-9) to dune habitat (plot 10-13) in Northwest China. The results showed that interveinal distance (ID) decreased with increasing water stress except that in plots of dune reed (DR). Vein mean diameter (VMD) in plot 10, 11 and 12 of the DR was significantly larger than that in other ecotypes. Leaf specific porosity (LSP) enhanced from plot 4 to plot 13 from heave salt meadow reed (HSMR) to light salt meadow reed (LSMR) and to DR. Chlorophyll fluorescence in bundle sheath cells were microscopically found in four ecotypes, especially significantly in the DR. Net CO2 assimilation rate (A (n)) dropped rapidly from the swamp reed (SR) to the HSMR and then increased progressively from the LSMR to the DR. Stomatal conductance (g (s)) decreased and the water use efficiency (WUE) rose from the wet to the dry ecotypes. Sensitivity of g (s) to intercellular CO2 concentration (C (i)) increased, but glycolate oxidase (GO) activity gradually reduced with increasing soil water deficiency. The RuBPCase activity did not reduce in four ecotypes even in DR, but, the PEPCase and NAD-ME activities as well as the ratio of PEPCase/RuBPCase were gradually enhanced with increasing soil water stress. We concluded that anatomical and photosynthetic carbon assimilating characteristics in P. communis were developing to the direction of C-4 metabolism in response to the increasing drought stress in desert areas. The DR enduring severe water stress had more C-4 like photosynthetic features than the HSMR and LSMR as well as SR, according to significantly increased VMD and LSP and higher g (s) sensitivity to C (i) as well as higher PEPCase activity and lower GO activity in the DR.