The interaction of competition for light and for nutrients

A new technique is described for the study of the interaction between competition for light and competition for a nutrient or for water. The technique was applied in a study of the competition between two grasses for light and for nitrogen. The aggressor species showed a negative interaction in the effect of the two modes of competition; it was slightly reduced in yield by competition for either factor alone, but when competition for both factors was operative, it achieved almost the same yield as in the absence of competition. The effect of the two modes of competition on the suppressed species showed a positive interaction; the depression in yield when there was competition for both factors greatly exceeded the sum of the effects of competition for the separate factors. An analysis is made of the nature of competition for one or more factors. Competition for even a single factor involves interaction between direct and indirect effects; when competition occurs for two factors, it leads to multiple interactions between two groups of effects and thus greatly intensifies the effects of competition for either factor operating alone.