Daily dynamics of gas exchange characteristics of three ephemeral plants in Dzungaria Desert
准噶尔荒漠3种短命植物气体交换特征的日变化

As pioneer plants, desert spring ephemerals play an important role in community succession, biodiversity maintenance and dune stabilization in desert ecosystems. We studied the diurnal changes in gas exchange of three desert spring ephemerals (Eremopyrum orientale, Malcolmia scorpioides, and Tetracme quadricormis, hereafter the genus names only) under natural conditions in the desert area of the Dzungaria Basin. Net photosynthetic rate (Pn) of the three ephemerals all reached the highest values at 12:00. Regarding the curves of diurnal variation, Pn of Eremopyrum and Malcolmia had two peaks, and an obvious midday depression occurred at 14:00; Transpiration rate (E) of all the three ephemerals had only one peak; water use efficiency (WUE) of Eremopyrum and Malcolmia had two peaks, and that of Tetracme had only one. One peak of WUE of all the three ephemerals occurred between 8:00 and 10:00, and the second peak of WUE of Eremopyrum and Malcolmia occurred between 16:00 and 18:00. Based on the tendency of changes in Pn, intercellular CO2 concentration (Ci) and stomatal limitation (Ls), we speculate that the midday depressions of Eremopyrum and Malcolmia were not controlled by stomatal factors, while those of Tetracme were. Daily mean values of Pn, E and WUE of Malcolmia and Tetracme were higher than those of Eremopyrum. The correlation analyses showed that the factors affecting Pn could be ranked as PAR > Gs > Ta > VPD > RH, and that the factors affecting E were different among the three ephemerals.