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 availabilit y above plant requirements can have detrimental effects by increasing soil nitrate concentrations, which can lead to increased N losses or increased a bundance of undesireable weedy plant species. The increase in nitrate conce ntrations following disturbance can be attributed in part to increases in p opulations 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 follow ing disturbance. Maintaining C-inputs to the soil following disturbance wil l allow continued microbial assimilation of N, which will minimize the adve rse affects associated with excess N availability.