Clonal Foraging in Perennial Wheatgrasses: A Strategy for Exploiting Patchy Soil Nutrients

Abstract

1 Foraging by means of plasticity in placement of tillers in response to low-and highnutrient patches was examined in the rhizomatous wheatgrass Elymus lanceolatus ssp. lanceolatus. Its ability to exploit soil nutrient patches was compared to that of the closely related but caespitose E. lanceolatus ssp. wawawaiensis. 2 Clones of 14 genets of each taxon were planted in boxes consisting of two 30 x 30 cm cells: the 'origin cell' where clones were planted, and the adjacent 'destination cell', with each cell containing soil with either low or high levels of nutrients. 3 The rhizomatous taxon, which can produce intravaginal, short-rhizome and longrhizome tillers, preferentially produced short-rhizome and intravaginal tillers in highnutrient destination cells. Effects of nutrient status of the origin cell as well as of the destination cell on total tiller numbers indicated clonal integration, yet tiller placement responded to local conditions. 4 Roots of both taxa accessed nutrients in destination cells (the caespitose subspecies by root growth only), and above-ground biomass of both taxa increased to a similar extent with high-nutrient destination cells. With the patch sizes used in this experiment, root growth was as important as ramet placement in exploiting nutrients in destination cells. 5 There was no relationship between degree of plasticity in ramet placement and biomass of the clone when high-nutrient destination cells were present.

On the evolution of clonal plant life histories

“…Benefits of plasticity in clonal traits have been shown in mathematical models, where plastically increased sexual reproduction was of advantage under poor conditions, because seed dispersal can act as an escape mechanism (Williams, 1975;Gardner and Mangel, 1999), and where growth form plasticity was of advantage, which enabled vegetative offspring to avoid occupied recruitment sites (Winkler and Schmid, 1995; see above for benefits of plastic foraging). Fitness benefits of plastic foraging have been experimentally confirmed in a heterogeneous competitive environment for a stoloniferous herb (van Kleunen and Fischer, 2001) but not for a grass with heterogeneously distributed soil nutrients (Humphrey and Pyke, 1997). However, field evidence for benefits of plasticity in clonal life-history traits is lacking.…”

“…Significant variation among genotypes of clonal plants has been reported for the allocation to sexual and vegetative reproduction (Schmid and Weiner, 1993;Prati and Schmid, 2000), for growth form and foraging, respectively (Cheplick, 1995(Cheplick, , 1997Humphrey and Pyke, 1997;Skalova el aI., 1997;Cheplick and Gutierrez, 2000;van Kleunen el (II., 2000a;van Kleunen and Fischer, 200 I), and for clonal integration (Alpert, 1999;van Kleunen el al., 2000b). These studies underline the importance of using several genotypes in studies on clonal life histories (de Kroon el al., 1994).…”

Ecology and Evolutionary Biology of Clonal Plants

“…Benefits of plasticity in clonal traits have been shown in mathematical models, where plastically increased sexual reproduction was of advantage under poor conditions, because seed dispersal can act as an escape mechanism (Williams, 1975;, and where growth form plasticity was of advantage, which enabled vegetative offspring to avoid occupied recruitment sites ; see above for benefits of plastic foraging). Fitness benefits of plastic foraging have been experimentally confirmed in a heterogeneous competitive environment for a stoloniferous herb (van Kleunen and Fischer, 2001) but not for a grass with heterogeneously distributed soil nutrients (Humphrey and Pyke, 1997). However, field evidence for benefits of plasticity in clonal life-history traits is lacking.…”

“…Significant variation among genotypes of clonal plants has been reported for the allocation to sexual and vegetative reproduction (Schmid and Weiner, 1993;, for growth form and foraging, respectively Humphrey and Pyke, 1997;Skalova et at., 1997;Cheplick and Gutierrez, 2000;van Kleunen et at., 2000a;van Kleunen and Fischer, 2001), and for clonal integration van Kleunen et aI., 2000b). These studies underline the importance of using several genotypes in studies on clonal life histories .…”

A developmental morphologist's perspective on plasticity

“…Clonal plants often have been used to examine the potential for integrated plastic responses to spatial environmental variability (see extensive discussion of clonal integration in the contributions by Alpert and Simms (2002), and Sachs (2002)). Physiological studies tend to show a high degree of integration among ramets (e.g., Lo¨tscher and Hay, 1997;Humphrey and Pyke, 1997;de Kroon et al, 1998;Stoll and Schmid, 1998). For example, nutrients tend to move from areas of higher to lower supply.…”