羊草种群对遮荫的适应性生长对策

Adaptive growth strategies of Leymus chinesis population in response to shading

自20世纪50年代以来,太阳到达整个地球的短波光能辐射量每10年减少2.7%,即"全球变暗",这会对植物及其所在的生态系统的功能产生影响,然而,目前关于这种影响的研究尚未得出一致的结论。本文利用不同程度的遮荫(0、30%、50%和70%)模拟全球变暗的效应,研究了我国北方草原优势植物羊草的种群密度、形态指标和光合生理等对遮荫的响应。结果表明:遮荫使羊草枝条密度有所降低,枝条高度明显增加,叶面积显著扩大,抽穗枝条比例即抽穗率升高;遮荫使羊草接受到的光合有效辐射显著下降,在0、30%、50%遮荫强度下羊草的气孔导度、光合速率和蒸腾速率仍表现出"午休"现象,而遮荫70%的处理下气孔导度、光合和蒸腾速率在11:00—16:00时间段均高于其他处理,而且光合和蒸腾速率未出现"午休"现象。这种"午休"现象的消失可能是一定程度遮荫或全球变暗导致某些植被系统生产力增加的重要原因之一。为更加准确预测各类生态系统对全球变暗的响应,必须针对更多地域、更多生境、更多类群和更多生育期植物对遮荫的响应开展实验研究,并加以整合和模拟。

Since the 1950s, the shortwaved solar radiation that the earth received has been reduced by 2.7% every decade, and this phenomenon is called ＆ldquo;global dimming＆rdquo;, which may impact plants and their inhabitant ecosystems. However, no consensus concerning such impacts has been reached. In this paper, different degrees （0, 30%, 50% and 70%） of shading were installed to simulate the global dimming effect to study the population density, morphological features （shoot height, leaf area, and heading rate）, and photosynthetic physiology （stomatal conductance, photosynthetic rate, and transpiration rate） of Leymus chinensis in response to shading. Shading decreased the shoot density somewhat, but increased the shoot height obviously, enlarged the leaf area significantly, and promoted the heading rate. Shading also significantly reduced the PAR that L. chinensis received. Under 0, 30%, and 50% shading, the afternoon depression in stomatal conductance, photosynthetic rate, and transpiration rate occurred. Under 70% shading, the stomatal conductance, photosynthetic rate, and transpiration rate at 11：00-16：00 were higher than those in other shading treatments, and the afternoon depression of photosynthetic rate and transpiration rate did not occur. The absence of the afternoon depression of photosynthetic rate and transpiration rate under 70% shading could be one of the main reasons of the increased productivity of some vegetation types after being shaded or being exposed to global dimming. To more precisely predict the responses of various ecosystems to global dimming, it would be necessary to conduct more empirical studies about the responses of plants to shading in more regions, with more habitat types and more plant functional types, and at more growth stages, and do more model studies and meta-analyses to incorporate the empirical data.