INCORPORATING THE SOIL COMMUNITY INTO PLANT POPULATION DYNAMICS : THE UTILITY OF THE FEEDBACK APPROACH

1 Although its importance for plant mineral nutrition and nutrient cycling has long been recognized, the soil community has rarely been integrated into dynamical frameworks of plant populations, in spite of abundant evidence for its involvement. The concept of feedback may provide theoretical and experimental tools for investigating the importance of the soil community in the population ecology and evolution of plants. 2 A mathematical model demonstrates the potential for two divergent dynamics, with positive feedback leading to the loss of diversity at a local scale and negative feedback leading to its maintenance. A linear contrast of the growth of plants in association with their own soil communities compared to the growth of plants in association with each others' soil communities can be used to differentiate between these possibilities in empirical studies. 3 Spatially explicit computer simulations demonstrate that the dynamics of a spatially structured community, as the soil community is likely to be, can differ from those predicted for a well-mixed population. Specifically, diversity can be maintained between locally homogeneous patches when positive feedback and dispersal occur at local scales. 4 Using a simple experimental protocol, we have found substantial negative feedback on plant growth through the soil community, suggesting that it may be involved in the maintenance of plant species diversity. 5 We discuss the importance of the soil community in other areas of plant ecology and evolution, including the suggestion that interactions with the soil community may be involved in the maintenance of sexual or asexual reproductive systems.

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