Selection of micro‐organisms in a spatially explicit environment and implications for plant access to nitrogen

Evolution of a microbial nitrogen‐uptake strategy that removes nitrogen at less than the maximum potential rate creates soil environments favourable for increased plant access to nitrogen. Plant productivity is thus increased, and achievement of maximum microbial biomass is facilitated through increased microbial access to plant‐derived carbon. Simulations show that micro‐organisms exhibiting such a ‘strategic’ nitrogen uptake will be competitively excluded by more voracious micro‐organisms in a homogeneous system, but can persist in a spatially explicit system. This persistence of less voracious micro‐organisms contrasts with the frequently held view that micro‐organisms in soil systems take up nitrogen at the maximum possible rate. The selection of strategic or voracious microbial types in a spatially explicit environment is sensitive to the frequency of plant and microbial disturbance, and to the rate of diffusion of inorganic nitrogen in the soil system. In particular, the strategic (less voracious) microbial types are favoured under conditions of low plant disturbance, low to moderate diffusion of inorganic nitrogen, and moderate microbial disturbance. When selection favours strategic microbial types, plant access to nitrogen is increased. Plants may also evolve strategies in a spatially explicit environment that will increase population densities of favourable, strategic microbial types.