The exploitation of heterogeneity by a clonal plant in habitats with contrasting productivity levels

Abstract

Summary 1 We investigated habitat exploitation by the rhizomatous grass Elymus repens in a heterogeneous environment in both productive and unproductive habitats. We tested whether there was selective entry of rhizomes into favourable microsites or random exploration of the habitat, and whether the benefits of selective exploitation were higher in productive than unproductive habitats. 2 Trays were divided into four quadrants around a common central area. Homogeneous environments were created by planting vegetation throughout the trays; heterogeneous environments were created by planting only centre and two opposite quadrants. Contrasting productivity levels were established by fertilizing half of the trays of each environment type. A single rhizome fragment of E. repens was planted in the centre of the trays and allowed to exploit the trays for two growing seasons. 3 Elymus repens effectively exploited habitat heterogeneity at both productivity levels. However, only unproductive trays showed preferential growth of rhizomes into bare quadrants. 4 In the productive trays individual rhizomes that grew into bare quadrants showed a significantly greater production of shoots and total biomass than those that grew into vegetated quadrants. Smaller, non‐significant effects were observed at lower productivity. 5 Increased growth of primary rhizomes, once they had entered a bare quadrant, with or without selective growth into these patches, led to similar increases in heterogeneous compared to homogeneous trays at the two productivity levels (3.0 vs. 2.7). Heterogeneity was not therefore more effectively exploited at high productivity. 6 We suggest that sectorial transport of nutrients through the rhizomes, resulting in directional outgrowth of bud meristems into the bare quadrants, may have been responsible for the selective placement of rhizomes in the unproductive trays. Our results suggest that selective entry of rhizomes into favourable microsites may complement morphological plasticity in enabling rhizomatous plants to forage in heterogeneous environments.