Morphological Plasticity in Clonal Plants: The Foraging Concept Reconsidered

Abstract

1 Studies of morphological plasticity in clonal plants have analysed responses to habitat quality in terms of spacer (stolon or rhizome internode) length and branching intensity. The capacity for these parameters to respond to environmental quality has been interpreted as an expression of foraging behaviour, as it confers the potential to intensify the placement of ramets in the more favourable microhabitats (patches) of a heterogeneous environment. This plasticity in clonal morphology is compared with similar responses of individual shoots and roots to habitat quality that have also been accepted as manifestations of foraging behaviour. 2 The most consistent morphological response shown by clonal species is a higher branching intensity an increased propensity of lateral meristems to grow out and form lateral rhizomes and stolons under conditions of higher resource supply. In contrast, spacer lengths show a variety of responses to light and nutrient availability, and many species exhibit no significant response. Even in stoloniferous species, where stolon internodes tend to shorten under higher photon flux densities, the degree of shortening may often be insufficient to elicit a significant concentration of ramets in favourable habitat patches. 3 Many clonal and nonclonal species have however, been shown to be very efficient in placing leaves and roots in areas of high resource supply within their environment. This is achieved by a high level of morphological plasticity of the shoot and root branches. 4 We therefore suggest that it is the highly plastic changes in the morphology of individual ramets that enable effective exploitation of local concentrations of essential resources once they have been located. The unresponsive spacer lengths of many clonal species may permit a continuous search of habitat space by the plant, rather than a selective placement of ramets. 5 The foraging concept is reformulated in more general terms relating to resourceacquisition strategies, so that it is applicable to both clonal and nonclonal species of plants.