Responses of the clonal Fragaria vesca to microtopographic heterogeneity under different water and light conditions

Vegetative multiplication allows clonal systems to spread horizontally and to establish (descendents) ramets in sites of contrasting resource status. Stolon or rhizome connections between ramets permit the transport of resources within the clone. As a result of such physiological integration, clones can act as cooperative systems, enabling buffering of any differences in resource supply among ramets due to local heterogeneity. This study tests the hypothesis that parent ramets of Fragaria vesca L. enhance their photosynthetic activity when connected to shaded or drought-stressed offspring ramets as result of the assimilate demand from those ramets. The study also investigated the extent to which small-scale topographic heterogeneity (i.e. offspring ramets at higher or lower level than parents) may influence the physiological integration, in terms of photosynthetic efficiencies, biomass and production of new ramets. Results showed that the photosynthetic efficiencies of parent ramets were increased in response to the assimilate demand made by drought-stressed offspring ramets, especially under shade conditions. We attribute this response to a mechanism of feed-back regulation in line with the source-sink hypothesis. We also found that offspring ramets at a raised topographic position with respect to parents showed a significant decline in the production of new ramets and a reduction in total biomass relative to offspring at a lower level or the same level. We conclude that microtopographic aspects of environmental heterogeneity may involve additional costs for ramet establishment of ramets. (C) 2007 Elsevier B.V. All rights reserved.