生境斑块对比度对鹅绒委陵菜克隆内分工的影响

PATCHY CONTRAST OF HABITAT AFFECTS INTRACLONAL DIVISION OF LABOR OF POTENTILLA ANSERINA

相互连接的克隆植物分株分别处于资源互补性的不同斑块时,将可能发生形态结构的特化,以更有效地吸收利用所处斑块中丰富的资源,形成分株的功能分化,即克隆内分工。生境的斑块对比度,作为资源或环境异质性的主要素,在一定程度上决定克隆内分工的发生状况。该文以鹅绒委陵菜(Potentilla anserina)为材料,在自然条件下将多组分株对置于不同的斑块对比度处理下,比较了它们克隆内分工的发生状态,试图发现分工与斑块对比度的关系,同时考察在克隆分工过程中分株的可塑性变化及其与分工的关系。该实验的理论假设是:分株发生分工的程度与分株所处斑块的资源对比度成正相关。研究结果表明,鹅绒委陵菜分株的高度和叶面积对局部光照环境产生强烈的可塑性反应,反应的结果是增加了对匮乏的光资源的获取。从分株根冠比和我们提出的分工指数来看,分工的程度在一定的斑块对比度范围内随斑块对比度的增强而增强,但到达一个最大值后又迅速降低。鹅绒委陵菜分株之间的分工和结构特化往往滞后于分株对所处局部环境的适应性可塑性变化,而后者往往在分株之间具有独立性和局部特征。克隆内分工主要依赖于生物量分配的调节而实现,其发生状态都是分株系统在分工收益、分工代价与分工风险之间权衡的结果,而这种结果在很大程度上取决于分株所处的斑块对比度。

Aims When interconnected ramets of clonal plants grow under reciprocal patches in terms of the availabilities of different resources, they likely specialize morphologically and functionally to exploit locally abundant resource（s） more efficiently. This phenomenon is known as division of labor. Patchy contrast is a critical component that partially determines the occurrence and magnitude of division of labor. We investigate the effect of patchy contrast on intraclonal division of labor and test the hypothesis that the magnitude of division of labor is positively correlated with patchy contrast. We also examine the association between adaptive plasticity and division of labor. Methods We subjected connected ramet pairs ofPotentilla anserina to reciprocal patchy environments with four levels of patchy contrasts, which were formed by providing ambient daylight but altering soil nutrient level for one ramet within each pair and providing a high soil nutrient level but changing light regime for the other. We measured shoot height, leaf area and shoot and root biomass. To quantify the magnitude of division of labor, we proposed an index based on root/shoot ratio （R/S） of ramets, namely, the ratio of difference between ramets in R/S to the sum of them. Important findings Shoot height and leaf area ofP anserina were highly plastic in response to local light availability, and such plasticity ultimately resulted in better ability to acquire scarce light resource, instead of abundant resource as predicted according to the rule of division of labor. This contradiction was probably due to the fact that the locally adaptive plasticity of shoot height and leaf area in response to local light environment took precedence over ramet specialization and division of labor, which was realized primarily by regulating biomass partitioning. The magnitude of division of labor peaked at the intermediate level of patch contrast and decreased both at the higher and lower levels. This pattern was likely an ultimate consequence of cost-benefit tradeoffs of ramet specialization. In conclusion, only when the benefits outweigh the costs at a certain patchy contrast, does division of labor occur, and there likely is an optimum patchy contrast that maximizes the division of labor. But under higher patchy contrast than the optimum one, division of labor may decrease as consequence of increased risks.