Preliminary Studies on Diurnal Variances of Physio-ecological Characteristics of Photosynthesis of Two Extreme Xerophytes——Reaumuria soongorica and Salsola passerina

Having long lived in rigor habitats,two extreme xerophytes Reaumuria soongorica(RS) and Salsola passerina(SP) formed special biological features and physio-ecological adaptations.The physio-ecological characteristics of photosynthesis of the two extreme xerophytes were studied under natural environment.The results indicated that there was physio-ecological plasticity in the photosynthesis of the two extreme xerophytes to a certain extent:(1) On August 22 when the environmental factors were more favorable for photosynthesis,the curve of diurnal variations of net photosynthesis rate(Pn) and transpiration rate(Tr) were dual-peaked(but not obviously) and Pn of RS was lower than that of SP.Pn on diurnal average value of RS and SP were(7.74±1.06) μmol·m~(-2)·s~(-1)and(5.56±1.71) μmol·m~(-2)·s~(-1) respectively.Tr of RS was also lower than that of SP,Tr on diurnal average value of RS was(24.38±6.2) mmol·m~(-2)·s~(-1)and(15.41±2) mmol·m~(-2)·s~(-1) in SP.Water use efficiency(WUE) was different from Pn and Tr,WUE on diurnal average value of SP(0.34 μmol·mmol~(-1)) was higher than that of RS(0.31 μmol·mmol~(-1))~()of RS.(2) But on September 28 when the environmental factors were less favorable for photosynthesis,the curve of diurnal variations of Pn and Tr changed to be single-peaked and their values were significantly reduced.The values of WUE on September 28 were higher than those of August 22.Through analysis on the variances of the physiological characteristics of small branches water potential,stomatal conductance and chlorophyll fluorescence parameters in leaves of two xerophytes,it was known that the photosynthesis in leaves was influenced by not only the stomatal factors but by the non-stomatal factors.