Clonal integration and plasticity in foraging behaviour in Glechoma hederacea

(1) The effects of subjecting different parts of Glechoma hederacea clones to different levels of light intensity and soil nutrient availability were investigated. The plastic responses of clonal morphology to different conditions were interpreted in terms of the degree and direction of photoassimilate and nutrient translocation between adjacent ramets along stolons and in terms of the degree of integration within the clone. It is suggested that experiments like this may provide viable alternatives to the use of radioactive tracers in elucidating translocation patterns within clones. (2) Low light intensity and low soil nutrient availability produced similar effects on clonal morphology, but light intensity appeared to exert the greater effect. Low availability of either resource resulted in extensive foraging whereas greater supply of resources resulted in more intensive foraging. (3) When individual clones grew from resource-poor conditions into resource-rich conditions, the morphology of the ramets developing along the stolon changed significantly as soon as growing conditions improved. In comparison, the change in ramet morphology along the stolon was more gradual when clones grew from resource-rich to resource-poor growing conditions. While local conditions largely determined the growth form of the developing ramets, this response was modified by the presence of priorestablished ramets, particularly when these were growing in more favourable conditions. (4) Results demonstrated considerable acropetal translocation of photoassimilates and nutrients along the stolons from established to developing ramets. When new ramets developed in resource-poor sites (low light, low nutrients), there was evidence that additional resources were translocated acropetally from prior-established, resource-rich ramets to growing ramets, enabling them to develop in a manner more characteristic of ramets growing in resource-rich rather than resource-poor conditions. The results provided no evidence of effective within-stolon basipetal translocation of resources between resource-rich and resource-poor parts of the clone, even when prior-established ramets were growing in resource-poor conditions. (5) In heterogeneous habitats acropetal support of ramets developing in unfavourable conditions results in them foraging more intensively than ramets of clones growing in uniformly unfavourable conditions. Acropetal translocation enables developing ramets to establish and survive, even if local growing conditions are unfavourable. Thus, in clonal species, integration between ramets enables the impact of local adverse selection pressures to be moderated.