Abundance of fungi and bacteria in a nutrient-impacted Florida wetland

Microorganisms have been proposed as early indicators of wetland change; however, there is often too little information to reliably use microbial parameters for this purpose. The objective of this study was to document how nutrient loading, plant community, and season affected arbuscular mycorrhizal (AM) fungi (expressed as percent colonized root length), other fungi (estimated by ergosterol concentration), and bacteria (quantified by direct counts) in soil and detritus, and thereby to broadly evaluate the potential of native microorganisms to serve as indicators of wetland integrity. Dominant wetland plant communities (Panicum, Cladium, Typha, Salix, mixed herbaceous, and deep-water slough) were sampled seasonally from nutrient-impacted and reference areas of a central Florida wetland with historic nutrient loading (only Cladium occurred in both impacted and reference areas). Nutrient impact increased soil and detrital ergosterol and bacterial counts in some plant communities and seasons (e.g., Cladium sampled in the fall); however, the nutrient effect was confounded by interactions with the plant community and season. Nutrient impact reduced AM root colonization in samples from impacted compared to reference Cladium communities during summer and fall; however, there were again significant interactions with season and other plant communities. We conclude that before soil fungi and bacteria can be used as indicators of wetland integrity background values for each plant community and season need to be well documented.