Edaphic properties, their heterogeneity, and associated microbial communities in headwater wetland complexes of the Ridge and Valley Region, Pennsylvania.

摘要

Small in area, headwater wetland complexes provide a disproportionate share of valuable ecosystem functions to the larger landscape. Through microbial biochemical cycling of large portions of the global carbon and nitrogen pools, they act as sinks for and transformers of inorganic nutrients and as sources of organic material to aquatic systems. Our current understanding of these systems suggests that anthropogenic activities have altered their hydrologic disturbance regimes with subsequent material fluxes and changed the structure of their biologic components (e.g., vegetation, macroinvertebrates, and birds). These changes can ultimately affect microbial biochemical cycling. In this dissertation I evaluated the condition of headwater wetland complexes, in terms of their edaphic properties, edaphic heterogeneity, and microbial communities in two landscape contexts, forested (> 80% forested) and mixed (< 50% forested), with mixed complexes also having a range of land use legacies. Edaphic properties and heterogeneity did vary between forested and mixed complexes. Edaphic heterogeneity measurements were higher in forested complexes compared to mixed complexes. The most homogenized complexes were those in mixed landscapes with past residential, cropland, and fill activities. In forested complexes the spatial heterogeneity of edaphic properties, most notably of soil organic matter (SOM) and soil moisture, were associated with a range of microbial habitats that varied in microbial biomass and composition. This range in microbial habitats was absent from complexes within mixed landscapes. In fact, these complexes, although left to reestablish after legacy land uses, were not necessary developing microbial communities similar to those in forested landscapes. This was evident through the differences between microbial community composition, pH, and soil texture classes of mineral soils across the landscape classes. The large difference in SOM accumulation between landscape contexts was further assessed by developing a method to characterize a portion of the labile SOM pool. This fraction was quantitatively and compositionally more sensitive to landscape context than SOM levels. The overall lack of SOM accumulation in mixed complexes was attributed to differences in vegetative community composition and structure (via temperature shifts), and hydrological regime shifts thought to affect litter quality inputs, decomposition rates, and/or the amount of scouring.