Crested wheatgrass growth and replacement following fertilization, thinning, and neighbor plant removal.

Abstract

The growth and annual replacement of crested wheatgrass (Agropyron desertorum (Fisch. ex Link) Schult.) tillers are affected by resource availability. Fertilization and grazing affect the resources available to crested wheatgrass plants directly, by increasing nutrient supply or by reducing photosynthetic area and root elongation, and indirectly, by changing the competitive status of neighboring plants. To determine the time and manner of crested wheatgrass response to alterations in resource availability, we assessed the growth, flowering, and replacement of tillers on plants treated as follows: tiller thinning, neighbor plant removal, combined thinning and neighbor plant removal, and nitrogen fertilization. These treatments were repeated on different sets of plants in early spring 1984 and 1985. Plant response was inferred from tiller heights, number of flowering culms, and new spring tiller production within the season of manipulation, and the number and heights of replacement tillers the following spring. Neighbor removal, and in 1 year fertilization, increased the size of tillers and stimulated the emergence of new spring tillers. Fertilization effects did not persist into the following year whereas neighbor removal increased annual tiller replacement at least two-fold on target plants. Tiller-tiller competition was not important in plants of crested wheatgrass because tiller growth and replacement on thinned plants did not differ from that of intact plants. This result occurred when thinned and intact plants were compared when both were growing with or without neighbors. Thinned plants replaced only the remaining tillers by the following spring. They did not regain their pretreatment status, presumably because of the encroachment of neighbors. These results indicate that thinned plants probably would lose their position in a plant community unless their neighbors are affected similarly.