杭州石荠苧的光合特性及其对土壤水分的响应

FEATURES OF THE PHOTOSYNTHESIS OF MOSLA HANGCHOWENSIS AND THE RESPONSE OF PHOTOSYNTHESIS TO SOIL WATER STATUS

本文通过控制土壤水分条件杭州石荠（Ｍｏｓｌａｈａｎｇｃｈｏｗｅｎｓｉｓ）光合的生理生态研究，解释了１９９３～１９９５年野外种群生态和生理生态研究中发现的问题，并分析了该种的濒危机制。结果表明：（１）杭州石荠的光饱和点较低，在土壤水分充足时仅３０ｋＬｕｘ左右。当土壤含水率从５％增加至２１％时，光饱和点、最大净光合速率和初始Ｐ／Ｌ值随之增加，而光补偿点则随之降低，但当土壤湿度超过２１％时，各参数的变化呈现出相反趋势。（２）在诸环境因子中，土壤含水率对光合速率的影响最显著，土壤从湿到干，光合土壤含水率回归直线的斜率增大，土壤湿度为６％时的斜率达１２．２２０８，是８％～１０％时的２～４倍和２４％～２５％时的６～９倍。（３）极端干旱时的水分利用效率最低，中等偏干时最高，湿润时又降低。（４）从光合特征值、解剖结构和叶绿素含量等判断，该种应属于Ｃ３光合类型、需光量介于阳性植物和阴性植物之间的耐阴植物。杭州石荠的上述光合生理生态特点及其它一些生物学特性，以及其分布地的环境之间的诸多矛盾可能是造成其濒危的主要原因之一。

The physiecological features of the net photosynthesis (Pn) of Mosla hangchowensis under controlled soil water status were studied,so as to answer the questions from the population and physiecological study in field in 1993～1995,and to analyze the mechanism of the species to be endangered.Results show that:(1) The saturation point of the photosynthesis of M.hangchowensis was low and was 30kLux in the moist soil.When soil water content (Sm)went up from 5% to 21%,the saturation point,maximum Pn and the initial P/L (Pn/light intensity)increased,while the compensation point dropped.But when Sm was over 21%,these parameters changed just contrary.(2) Among the environmental factors,the effect of the Sm on Pn was the most significant.From wet to dry,the value of b of the regression equations between Pn and Smincreased,It was as high as 12.2208 when the content of water in soil was 6%,being 2～4 times higher than the water content was 8%～10% and 6～9times higher than the water content was 24%～25%.(3) Water utilization efficiency (WUE) was lowest when soil was extremely dry,highest when soil was medium or drier and decreased when soil was wet.(4) The photosynthesis characters and the chlorophyll content implies that M.hangchowensis was a shade tolerant herb,which interposes between the heliophytcs and the sciophytes and it belonged to the C 3 type of photosynthesis.The contradictions among the photosynthetic features,the bio ecological characters and the environment in which M.hangchowensis distributed may be one of the main causes which made it endangered.