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

1 We investigated habitat exploitation by the rhizomatous grass Elymus repe ns in a heterogeneous environment in both productive and unproductive habit ats. We tested whether there was selective entry of rhizomes into favourabl e microsites or random exploration of the habitat, and whether the benefits of selective exploitation were higher in productive than unproductive habi tats. 2 Trays were divided into four quadrants around a common central area. Homo geneous environments were created by planting vegetation throughout the tra ys; heterogeneous environments were created by planting only centre and two opposite quadrants. Contrasting productivity levels were established by fe rtilizing half of the trays of each environment type. A single rhizome frag ment of E. repens was planted in the centre of the trays and allowed to exp loit the trays for two growing seasons. 3 Elymus repens effectively exploited habitat heterogeneity at both product ivity levels. However, only unproductive trays showed preferential growth o f 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 quadra nt, with or without selective growth into these patches, led to similar inc reases in heterogeneous compared to homogeneous trays at the two productivi ty levels (3.0 vs. 2.7). Heterogeneity was not therefore more effectively e xploited at high productivity. 6 We suggest that sectorial transport of nutrients through the rhizomes, re sulting in directional outgrowth of bud meristems into the bare quadrants, may have been responsible for the selective placement of rhizomes in the un productive 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.