INTRASPECIFIC COMPETITION IN CHENOPODIUM-ALBUM VARIES WITH RESOURCE AVAILABILITY

The intensity of intraspecific competition under different levels of light and nitrogen supply was assessed for the temperate zone herb, Chenopodium album Plants were grown at two densities (one or six plants/pot) in a modified factorial design with three levels each of light and nitrogen availability. This yielded five light/nitrogen treatments which comprised two gradients, one extending from low light and nitrogen to conditions of high light and nitrogen, the other from conditions of low light/high nitrogen to conditions of low nitrogen/high light. Competition among plants grown six per pot significantly affected growth in all treatments and was most intense where resource supply was greatest. When one or both resources were limiting, competition was less intense. This pattern held whether assessed for total biomass, aboveground biomass, or belowground biomass only. Thus, it seems that the relative amount of resource limitation, not the source (light or nitrogen Limitation), determined the intensity of intraspecific competition for this species. Those resource conditions most conducive to intense competition were also the most conducive to high productivity (dry biomass of plants grown alone). The pattern of competitive intensity observed in Chenopodium album suggests that the intensity of intraspecific competition is greatest under optimal resource conditions. We suggest that patterns of intraspecific competition may be important in community dynamics, and that the interpretation of future interspecific competition studies would be more complete if intraspecific competition were also considered.