| The in vivo photosynthetic traits at the stage switched from vegetative to reproductive growth of spring ephemeral species,which widely distributed in the Junggar Desert of Xinjiang,were measured by an open gas-exchange measurement system (Li-6400). The diurnal changes of photosynthesis and fluorescence in four ephemeral species belonging to two life forms were compared and the biomass allocation traits, leaf mass ratio and root activity of several annual ephemeral species were analyzed. The main results indicated:1) Maximum net photosynthesis rate (Pn),transpiration rate (Tr) and instantaneous water use efficiency (iWUE) of 16 spring ephemeral species ranged from 8.07 to 35.96μmol CO2·m-2·s-1, 3.16 to 29.64mmol H2O·m-2·s-1 and 0.54 to 4.26μmolCO2·mmol-1H2O, respectively. Maximum Pn was positively correlated with maximum stomatal conductance (Gs), the correlation coefficient was 0.77 (p<0.05) and the slope in the linear region was 26.36μmol·mmol-1. Based on the analysis for the response of Pn to internal CO2 concentration and to photosynthetic photon flux density, the apparent CO2 compensation point are in the range of 4 to 5 Pa (ambient air temperature of 28 ~ 30℃during the measurement), the apparent carboxylation efficiency is ranged from 0.64 to 1.86μmolCO2·m-2·s-1·Pa-1, and the apparent quantum yield is ranged from 0.05 to 0.06.2) Two annual ephemeral species (Heteracia szovitsii Fisch. et Mey. and Malcolmia africana (L.) R. Br.) had one peak of Pn, Tr and Gs during a sunny day, while two perennial ephemeral species (Tulipa tianschanica Regel and T. dasystemon (Regel) Regel) had two peaks. Depression of photosynthesis was observed in T. tianschanica and T. dasystemon, primarily due to decrease of Gs and down-regulation of the photochemical efficiency. The daily mean values of Pn, Tr, Gs and electron transfer rate in two annual species were higher than that in two perennial species, but the daily mean values of iWUE and non photochemical quenching were lower than that in two perennial species.3) The data analysis of biomass allocation showed that individual biomass, total leaf area and root/above biomass ratio of seven annual ephemeral species which growing in both Gobi desert and sandy dune were very low, while leaf mass per unit leaf area and leaf area ratio of these species were high. Besides, the percentage of total biomass allocated to roots was positively correlated with iWUE in seven species growing in Gobi desert (r=0.93, p<0.01), while root activity is negatively correlated with iWUE (r= -0.667, p<0.01).The photosynthetic characteristics of the investigated spring ephemeral species indicated that they were typical C3 plants. Those spring ephemeral species are characterized by higher Pn, Tr and lower iWUE in comparison with other desert species. The unique biomass allocation of low root/above biomass ratio, higher leaf area ratio and leaf mass per unit leaf area of spring ephemerals species, as well as the photosynthetic traits, are involved in the physiological mechanisms contributed to their especially fast growth rhythm.
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