Gas exchange characteristics of Reaumuria soongorica from three geographical populations.

【Objective】 This paper researched diurnal change characteristics of phtosynthsis and transpiration of Reaumuria soongorica from three geographical populations,and analysed their characteristics of water use efficiency(WUE) and their reaction mechanism to drought stess.【Method】 Using portable photosynthesis analysis system,the gas exchange characteristics such as the net photosynthetic rate(Pn),transpiration rate(Tr) and stomatal conductance(Gs) diurnal changes of R.soongorica from three geographical populations(LZJ,WWM,and ZYL) were studied from July to August under natural environment.【Result】 The net photosynthetic rate and transpiration rate diurnal changes of R.soongorica from LZJ,WWM and ZYL were all bimodal,and there was the phenomenon of midday depression at 13:00.The Pn and Tr of R.soongorica from ZYL and WWM where had lower water condition such as annual mean precipitation(AMP) and soil water content(SWC) were lower than that of LZJ,and the maximum Pn and Tr of R.soongorica from ZYL and WWM presented at 09:00 that was one hour advanced than that of LZJ,and the time of midday depression was prolonged,but the Pn and Tr of R.soongorica from three geographical populations were all low and their phtosynthetic types were low Pn and Tr.The phenomenon of midday depression(09:00(10:00)-13:00) of R.soongorica from three geographical populations resulted from the stomatal factors,and the non-stomatal factors contributed much to the rising in the morning(07:00-09:00(10:00))and the decline in the afternoon(15:00-18:00) of Pn.WUE of R.soongorica from three geographical populations were also bimodal and rose with the lowering of water condition.【Conclusion】 The diurnal changes of gas exchange characteristics of R.soongorica from three geographical populations have some generality,but also have difference.Water condition is the main factor that causes the difference.R.soongorica is the desert plant that adapts to the adverse circumstances by reducing Tr and increasing WUE.