关键词: 旧水, 同位素, 喀斯特, 水文路径, 养分流失

Abstract: In arid areas, small rainfall (≤5 mm) events account for a large proportion of annual precipitation frequency, and occur in short time intervals. To elucidate the possible strategies of desert plants in utilizing small rainfall, this paper studied the photosynthetic responses of 28 plant species to simulated 1 and 6 mm rainfalls in Junggar Basin of Northwest China. For comparison, the 28 species were grouped into four plant functional types, i.e., herbaceous plants with short life cycle, herbaceous plants with long life cycle, nonphreatophyte shrubs, and phreatophyte shrubs. The results showed that after 1 mm rainfall, the net photosynthetic rate (P_n) and stomatal conductance (g_s) of most herbaceous plants increased, while the g_s of nonphreatophyte shrubs and the instantaneous water use efficiency (WUE) of phreatophyte shrubs had a response magnitude similar to that after 6 mm rainfall. In order to explore the possible mechanisms of small rainfall utilization, the leaf water uptake content (LWUC) and the percentage increase of leaf water content (R_w) were measured for assessing the leaf water uptake capacity of all the test species. The results revealed that most herbaceous plants with trichomes could directly absorb small rainfall, while shrubs could be indirectly benefited via increasing the humidity of microhabitat, regulating stomatal conductance, and reducing transpiration.

Key words: hydrological pathway, karst, old water., nutrient loss, isotope