Mutualism and competition between plants and decomposers: implications for nutrient allocation in ecosystems.

By examining the consequences of simultaneous mutualism and competition between plants and decomposers, we show that testable predictions about nutrient allocation in ecosystems follow from the assumption that decomposers allocate for their own growth the fraction of mineralized nutrient that maximizes their population biomass, leaving the remainder available for plant uptake. Available data for a wide variety of ecosystems are nearly all consistent with the predicted quantitative relationships among nitrogen flow rates and nitrogen fractions in plants, decomposers, and nonliving organic matter. Our predictions are robust against changes in the detailed structure of the nutrient-cycle models we use for our derivations.