Effects of disturbance on microbial activity and N-cycling in forest and shrubland ecosystems

Disturbances involving removal or destruction of plant biomass or mixing of soil typically increase nitrogen (N) availability. Increased N availability above plant requirements can have detrimental effects by increasing soil nitrate concentrations, which can lead to increased N losses or increased abundance of undesireable weedy plant species. The increase in nitrate concentrations following disturbance can be attributed in part to increases in populations and activity of nitrifying bacteria, but an even more important cause appears to be a reduction in rates of assimilation of nitrate by soil microorganisms. This decline in microbial assimilation rates appears to be direct result of smaller amounts of belowground plant carbon-inputs following disturbance. Maintaining C-inputs to the soil following disturbance will allow continued microbial assimilation of N, which will minimize the adverse affects associated with excess N availability.