EFFECTS OF NUTRIENT PATCHES AND ROOT SYSTEMS ON THE CLONAL PLASTICITYOF A RHIZOMATOUS GRASS

Clonal plant foraging has been examined primarily on individual clones exposed to resource-poor and resource-rich environments. We designed an experiment to examine the clonal foraging behavior of the rhizomato us grass Elymus lanceolatus ssp. lanceolatus under the influence of ne ighboring plant root systems in a heterogeneous nutrient environment. Individual Elymus clones were planted in large bins together with one of three neighboring grass species, Agropyron desertorum, Pseudoroegne ria spicata, or Bromus tectorum, which differ in rooting density and g rowth activity. The position of Elymus clones was manipulated so rhizo mes encountered a short-duration nutrient patch and subsequently root systems of the neighboring plants. Unexpectedly, the morphological pla sticity of the perennial grass Elymus lanceolatus ssp. lanceolatus was influenced by the presence of the neighboring species much more than by the local nutrient enrichments, although nutrient patches did ampli fy some of the foraging responses. Elymus rhizomes branched readily an d initiated large daughter plants as they encountered the low-density root systems of Pseudoroegneria. When Elymus encountered the fine, den se root systems of the annual Bromus, clonal expansion was initially r educed. Yet, after the short growing season of Bromus, Elymus resumed clonal expansion and produced several daughter plants. Elymus clones w ere most constrained by the fine, dense root systems of Agropyron dese rtorum. In this case, a few, long rhizomes avoided the densely rooted soil environment by growing aboveground as stolons crossing over the A gropyron tussocks. Elymus clonal biomass was largest in neighborhoods of Pseudoroegneria, intermediate in neighborhoods with Bromus, and sma llest in neighborhoods with Agropyron. The latter were approximately h alf the size of those in the Pseudoroegneria environments. Elymus grow th could not be explained by simple resource competition alone; other mechanisms must have been involved in the apparent differences in inte rference patterns of neighboring plants with Elymus.