浑善达克沙地典型灌木和草本植物对模拟降雨的不同反应

为了探讨不同生活型对瞬时降雨的适应策略,比较了浑善达克沙地常见灌木羊柴(Hedysarum fruticosum Pall.)和其共生草本植物猪毛菜(Salsola callina Y.L. Chang)在降雨解除干旱后的生理生态反应.光合速率(Pn)、蒸腾速率(E)、气孔导度(gs)、PSⅡ最大光化学效率(Fv/Fm)和叶片水势(ψleaf)均随着模拟降雨量的增加而增大;羊柴的水分利用效率(WUE)随降雨量的变化不大,而猪毛菜的WUE却随降雨量的增加一直处于下降趋势.两种植物的Pn和Fv/Fm都在雨后3 d完全恢复,而gs和ψleaf却提前1或2 d恢复,这说明气孔和非气孔因素综合限制了羊柴和猪毛菜的同化速率.两种植物对模拟降雨量的反应方式不同,15 mm的雨量就使羊柴的Pn、E和gs达到最大值,而猪毛菜却随着雨量的增加一直增大.我们认为,羊柴和猪毛菜对于模拟降雨的反应在时间上具有同步性,但对雨量的反应方式却不一致,猪毛菜对水分的利用不经济且瞬时反应,而羊柴可以被认为是节约型用水植物.

Differential Responses to Simulated Precipitation Exhibited by a Typical Shrub and a Herb Coexisted in Hunshandak Sandy Land

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.