Effects of soil phosphorus level on morphological and photosynthetic characteristics of Ageratina adenophora and Chromolaena odorata
比较研究了紫茎泽兰和飞机草的生长、形态、生物量分配和光合特性对磷营养的可塑性反应，及与其入侵性的关系.结果表明，两种入侵植物对磷营养变化表现出很强的可塑性和适应性.低磷时，两种植物的根生物量比增大，利于养分吸收；高磷时，两种植物的比叶面积、最大净光合速率、光饱和点、单位面积的叶绿素和类胡萝卜素含量增大，同化面积和同化能力增强，利于碳积累.相比之下,紫茎泽兰对磷的适应性更强.随供磷量的增加，紫茎泽兰和飞机草的相对生长速率、总生物量、株高、分枝数、叶面积指数和最大净光合速率均显著增大，过量磷素对上述参数抑制较小，表明两种入侵植物偏好较高的磷环境，土壤磷含量升高有利于其入侵，并在高磷时，通过增大株高、分枝数和叶面积指数荫蔽排挤本地种.在本地种基本停止生长的干季，紫茎泽兰和飞机草仍维持较高的相对生长速率.这也与其入侵性密切相关.
In this paper,a comparative study was made on the growth,morphology, biomass allocation,and photosynthesis of two invasive plant species Ageratina adenophora and Chromolaena odorata under five soil phosphorus levels,aimed to know how the test plant species acclimate to the changes of soil phosphorus level,evaluate which plant traits were associated with the invasiveness of the two species,and know whether the increased level of soil phosphorus could facilitate their invasion.The results showed that the two species had considerable phenotypic plasticity and ?phosphorus acclimation ability.At low phosphorus levels,their root mass ratio increased,which could enhance the nutrient capture ability,while at high phosphorus levels,their specific leaf area,maximum net photosynthetic rate,light saturation point,and chlorophyll and carotenoid contents per unit area were high,and the assimilative capacity and area increased,which could facilitate their carbon gain.A.adenophora had higher phosphorus acclimation ability than C.odorata.With the increase of phosphorous level,the relative growth rate,total biomass,branch number,leaf area index,and maximum net photosynthetic rate of the two species increased significantly,and most of the parameters were not decreased significantly under over-optimal phosphorus level.The two species could grow better under high phosphorus levels which were usually excessive and/or harmful for most native species,and enhanced soil phosphorus level might promote their invasion.At high phosphorus levels,the two invasive plant species might shade out native species through increasing their plant height,branch number,and leaf area index.The two species could maintain relatively high growth rate under high phosphorus levels in dry season when native plant species almost stopped growing.The ability that the invasive plant species could temporally use natural resources which native plant species could not use was also associated with their invasiveness.
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