Experimental derivation of functions relating growth of Arabidopsis thaliana to neighbour size and distance

1 A dynamic competition kernel for a plant growing in the presence of a neighbour is a function describing how the competitive effect experienced by the plant depends on its own size, and the size of and distance to a neighbour. Competition experiments on Arabidopsis thaliana were used to derive dynamic competition kernels for this species. 2 The experiments entailed growing target plants in isolation, and with single neighbours of different relative sizes, and at different distances. Growth was determined from repeated measures of the area occupied by each plant. Target plants with smaller neighbours, or with neighbours that were further away, grew to a larger size than targets with larger, or closer, neighbours. 3 Relative growth rate (RGR ) of isolated plants was best described by the Gompertz equation, a standard plant growth equation that reduces RGR in proportion to the logarithm of plant size. 4 Competition kernels were constructed by modifying the Gompertz equation to include the competitive effect of a neighbour. Alternative kernels (including the zone of influence model), with and without a parameter of asymmetry of competition, were constructed from observed growth rates of target plants with neighbours over short time intervals. The kernels were evaluated based on their ability to predict the size of targets and neighbours over a much longer time period. 5 The kernel that best described growth overall was a simple function proportional to the logarithm of neighbour size, and decreasing with distance to the neighbour. The zone of influence model was best able to describe the effects of distance on competition, but was relatively unsuccessful when the two plants differed substantially in size. Including a parameter for asymmetry did not provide any notable improvements in predictive ability, and in many cases made the predictions worse.