Resistance of the Microbial Community within Salt Marsh Soils to Selected Perturbations

The response of the soil microbial community in a short Spartina alterniflora salt marsh to selected, long term perturbations was examined. Alternative hypotheses of linkage between macrophyte production and the microbial community biomass and activity were tested. In 2 perturbation experiments macrophytic primary production was removed from marsh plots by clipping shoots and printing beneath ground parts for periods up 10 18 mo. In a third experiment monthly enrichments of glucose, ammonium nitrate and their combination were made for 5 mo to both clipped and pruned plots as well as unclipped control plots. The state of the microbial community was monitored by adenosine triphosphate and total adenylate concentration, community adenylate energy charge ratio and anaerobic uptake of ¹ ⁴C—glucose by mud slurries. The overall responses of the various parameters were consistent with the hypothesis that the soil microbial community is relatively unlinked to plant growth. This "unlinking" appears responsible for the observed resistance to change by the microbial community in the face of perturbations to the marsh system. Two mechanisms of resistance were postulated. First, while the microbial community resides in a large reservoir of organic matter, most of this organic matter may be relatively refractory. Hence, the microorganisms would be nutrient limited by the slow transformation of this material. Such a large resource pool with a long turnover time would promote resistance to perturbations that alter plant productivity. Second, the microbial community would be resistant to changes rather than nutrient status if in fact it were limited by physiochemical, spatial constraints rather than nutrients. While neither hypothesis could be totally rejected, our results give greater support to the second hypothesis.