干旱胁迫对高山柳和沙棘幼苗光合生理特征的影响

为了解干旱河谷-山地森林交错带植物光合生理特征对干旱胁迫的响应。以交错带两种典型植物高山柳(Salix paraqplesia)和沙棘(Hippophae rhamnoides)为研究对象,研究其在不同程度的干旱胁迫条件下植株气体交换参数的日变化特征。干旱胁迫显著降低了两种植物叶片数、叶面积、叶片生物量、比叶面积、色素含量、净光合速率(Pn)、气孔导度(gs)和气孔限制值(Ls)等与光合生理过程密切相关的叶片指标,但增大了胞间CO₂浓度(Ci)和内禀水分利用效率(WUEi)。植物叶片的气体交换参数(如:Pn和gs)日变化并未完全随着光合有效辐射的增强和温度的升高而增加,全天以11:00最大,"午休"现象明显。相对而言,沙棘在干旱胁迫条件下表现出相对较高的叶面积、Pn、gs和WUEi,具有相对更强的适应干旱环境的能力,而高山柳对干旱胁迫更为敏感。

Effects of drought stress on the photosynthesis of Salix paraqplesia and Hippophae rhamnoides seedlings

Increasingly drought is changing the structure and function of terrestrial ecosystem and as a consequence of which numerous studies have focused on the responses of plants to drought stress in the dry area. Photosynthetic process is an essential process in plant growth, which is sensitive to environmental change. Many evidences have documented that Minjiang dry valley at the upper reaches of Yangtze River is expanding upward as affected by human activity, environmental changes and their interactions under the global climate change scenarios. The ecotone between dry valley and mountain forest is honored by "the last defense" in slowing or restraining the expansion of dry valley, which is also one of the heavy destroyed areas in the "5.12" Wenchuan earthquake. In order to understand the effects of drought on the plant photosynthesis in the ecotone,(Salix paraqplesia and Hippophae rhamnoides), which are two representative plants, were selected to study leaf morphological characters and the diurnal dynamics of leaf gas exchange under the treatments with different drought stress (control: 80% water field capacity (FC), moderate drought stress: 40% FC, and severe drought stress: 20% FC). The controlled water experiment was arranged in the typical ecotone at Jiashan village of Li county (31°32'N, 103°26'E) in Sichuan Province. Five individuals of S. paraqplesia and four individuals of H. rhamnoides were dead under severe drought stress (20%FC) during the drought stress experiment. Drought stress significantly decreased the leaf number, leaf area, leaf mass, specific leaf area, the content of chlorophyll and carotenoids, net photosynthetic rate (Pn), stomatal conductance (gs) and stomatal limitation value (Ls), which are greatly related to the photosynthetic processes of both S. paraqplesia and H. rhamnoides. However, intercellular CO₂ content (Ci) and intrinsic water use efficiency (WUEi) increased with the increase in drought stress. Leaf gas exchange parameters such as Pn and gs were not increased with the increase of photosynthetic photo flux density and air temperature. The maximum of Pn and gs were observed at 11:00 hrs, and the "midday depression" was also observed in these two species. In addition, compared with S. paraqplesia, H. rhamnoides displayed relative higher leaf area, Pn, gs and WUEi under drought stress treatments, indicating that H. rhamnoides is better adapted to drought environment, while S. paraqplesia is more sensitive to drought stress. The results suggested that the plant at the ecotone might receive strong effects under increasing drought conditions as affected by climate change in the future. Drought significantly decreases the photosynthetic efficiency of S. paraqplesia and H. rhamnoides at the ecotone, and leading to decreased plant growth. However, the responses to drought stress were inconsistent between two thespecies. Compared with S. paraqplesia, H. rhamnoides showed relatively greater adaptation to drought environments with higher leaf area, Pn, gs and WUEi. The results from this study provide information for plant selection and species arrangement in relation to vegetation improvement management in the ecotone between Minjiang dry valley and mountain forest.