Abstract:

To assess the ecophysiological responses and adaptive strategies to rainfall exhibited by different plant functional types, we compared gas exchange, leaf water potential (Y_leaf) and PSⅡ photochemical efficiency (Fv/Fm) between Hedysarum fruticosum Pall. (shrub) and Salsola collina Y. L. Chang (herb) under a series of simulated rainfalls. The experiment was conducted in Hunshandak Sandy Land, North China. The values of net photosynthetic rate (P_n), transpiration rate (E), stomatal conductance (g_s), Fv/Fm and Y_leaf always elevated with the increasing amount of simulated rainfall. Whereas water use efficiency (WUE) maintained constant in H. fruticosum while always decreased in S. collina. Both species fully recovered their P_n and Fv/Fm 3 d after rainfall, while g_s and Y_leaf recovered only within 2 d. However, the response patterns were obviously different. H. fruticosu promote its physiological traits within 5-15 mm rainfall but no further positive enhancement was noted when rainfall was larger than 15 mm. In S. collina, however, the enhancement continued with more water applied. We inferred that H. fruticosum and S. collina responded similarly to rainfall in time courses but differential to simulated precipitation change. S. collina was likely to be physiologically sensitive to instant increasing soil water, that can be regarded as a prodigal water use type; whilst H. fruticosum was a conservative water user.

Key words: gas exchange, leaf water potential (Y_leaf), Hedysarum fruticosum , Salsola collina , Hunshandak Sandy Land