The effects of spatial pattern of nutrient supply on the early stages of growth in plant populations

1 We report an experimental study of the effects of pattern of nutrient supply on the early stages of growth in populations of Cardamine hirsuta. Populations were grown with nutrients provided in one of four spatial patterns (three heterogeneous and one homogeneous). In the three heterogeneous treatments, nutrient-rich and nutrient-poor substrate patches of different sizes were set up in chequerboard patterns, with patches of each type accounting in total for half of the substrate, both by volume and area. All treatments provided the same total quantity of nutrients. 2 After 31 days of growth, populations in the heterogeneous treatments had produced significantly more root, shoot and total biomass than those in homogeneous conditions. The coefficient of variation in shoot sizes, and the variation in root biomass per unit of substrate, were also significantly greater in populations growing under heterogeneous conditions. In the heterogeneous treatments significantly more than 50% of the biomass was located in nutrient-rich patches, and this proportion increased significantly as patch size increased. 3 In heterogeneous treatments, yield of plant parts from nutrient-rich locations was significantly greater than that of plant parts in nutrient-poor locations. It was also significantly greater than that recovered from equivalent locations in the homogeneous treatment. 4 We conclude that the spatial configuration of nutrients significantly affects plant population yield, the spatial distribution of population biomass, and plant size hierarchy during the early stages of population growth, even when total nutrient supply is held constant. We predict that these early effects of heterogeneity will continue to have impacts, not only on size structure, but also on the spatial pattern of mortality and the overall level of mortality, at later stages of population growth.