COMPETITION Dynamics of Competition between Wheat and Oat I. Effects of Changing the Timing.pdf

COMPETITION Dynamics of Competition between Wheat and Oat: I. Effects of Changing the Timing of Phenological Events Roger D. Cousens,* Allan G. Barnett, and Geoffrey C. Barry ABSTRACT The identification of such traits has usually involved correlation analyses between final yield and morpholog-Supply and demand for resources change dynamically throughout ical descriptors of plants at maturity or at some arbitrarythe growing season. If we are to understand the differences in competi- earlier stage (e.g., Reeves and Brooke, 1977; Balyan ettiveness among crop cultivars, we need to study the dynamics of species interactions, not just their outcomes. We examined the tempo- al., 1991; Lemerle et al., 1996). Such simple correlations, ral patterns in competition between wheat (Triticum aestivum L.) however, ignore the dynamics of competition. By defini- and oat (Avena sativa L.) in a series of field experiments. The com- tion, competition occurs when plants take up resources bined effects of shifts in height growth and phenological development that are in limited supply. Resources vary in availability were described for monocultures and mixtures by varying the sowing throughout the year; different resources will vary in the dates of the species. Similar observations were made for oat competing timing and extent to which they become limiting. Forwith wheat lines differing in flowering time and for wheat competing example, competition for nutrients may begin early,with a range of Avena taxa. In contrast to earlier work, no reversals whereas water may not become limiting until after an-of competitive hierarchy were seen during the season. The species that thesis; uptake of a resource early in the season when itachieved the greater biomass early on remained the better competitor is not limited may intensify competition for it muchthroughout growth. The hypothesis that a delay in emergence will move the timing of such reversals was thus not supported. There were later. Remarkably