The effects of spatially heterogeneous nutrient supply on yield, intensity of competition and root placement patterns in Briza media and Festuca ovina

1. An experiment was carried out to determine whether the spatial pattern of soil nutrient distribution influences plant growth and root placement, and the intensity of competition between plants. Our hypotheses were that (i) growth would be greater for plants in heterogeneous than homogeneous conditions (ii) competitive intensity would be greater when nutrients were confined to a small proportion of the substrate volume than when uniformly distributed, and (iii) plants would selectively place roots in nutrient-rich patches in heterogeneous conditions. 2. We grew plants of Briza media and Festuca ovina alone, or with an intra or interspecific competitor, in pots in which the same total supply of nutrients was distributed either homogeneously or heterogeneously. Nutrients in the heterogeneous treatment were confined to three soil cores occupying only 6.5% of the substrate volume. 3. Pattern of nutrient supply did not affect yield of plants grown alone. However, the reduction in target plant yield caused by competition was much greater in heterogeneous than homogeneous conditions (i.e. competitive intensity was greater in heterogeneous conditions). 4. Plants growing in heterogeneous conditions placed roots preferentially in the nutrient-rich substrate patches. This may have been the cause of greater competitive intensity in heterogeneous conditions. It is speculated that soil-based heterogeneity might exert an important influence on community structure and composition through its effects on competition.