Ecological legacies from grasslands to agroecosystems : microbial ecology, plant community assembly, and resource allocation
Large scale soil degradation is pervasive across the modern landscape. The expansion of municipal infrastructure and the legacy effects of agriculture play key roles in the continued alteration of the soil profile. The response of the soil physical, chemical, and biological properties along with the plant community composition in response to land-use changes is poorly understood. These ecological variables are often compared to like compositions and ecological structures (i.e., agricultural soils to agricultural soils, forested soils to forested soils), but rarely compared to what once was, the native state prior to large scale manipulation of the landscape. The goal of this study has been to compare what soil once was to what it is at present. In this case, the once vast prairie soils and plant communities of Missouri to the degraded soils of agriculture whether currently active or not. The variables considered within this research were 1) the microbial communities of remnant, restored, and reconstructed prairie communities, 2) the potential soil nutrient environment or "nutrient spectrum" associated with three common species of plants found in remnant, restored, and reconstructed prairies, and 3) the comparative ability of carbon (C) and nitrogen (N) allocation between common Missouri crops and their native analogs, sharing the same photosynthetic and morphological distinctions. Within this dissertation I found remnant soils and floristic communities are distinct from more degraded prairie states (restorations and reconstructions). Microbial community biomass is highest in remnant sites and depletes along a degradation gradient from remnant to restored and finally reconstructed sites having the lowest overall microbial biomass. The same is true of soil nutrients and species quality and quantity metrics along the same gradient. For instance, I found the quality of plant communities within remnant grassland systems was largely unchanged, regardless of nutrient status. This was not the case for sites with altered soil profiles. In addition, legacy effects of agriculture play a role in the outcome of restoration practices, leading to variability in the plant communities that can establish in a given site. Finally, C and N allocation among common midwestern crops and native prairie analogs was variable across time within a growing season. A comparison of legumes yielded significantly different concentrations of C and N across a growing season, yet their allocation timing was similar. This was not true of C4 grasses by comparison. There were significant differences in allocation strategies in both timing and concentrations across tissues and seed. Across these studies, I conclude the juxtaposition of what the soil ecosystem once was (e.g., the ecological reference state) to what it is at present is a valuable ecological comparison. This approach has far-reaching implications, especially as sustainability is at the forefront of current research. I advocate that the sustainability of the current land use model is dependent on a thorough understanding of the attributes the remnant state represented in the not-so-distant past. The remnant state may not be capable of providing for current societal needs, but it holds ecological information that can ensure a more sustainable path forward. This dissertation presents what has been lost, gained, or maintained across a wide ecological gradient. This dissertation accounts for human alteration of the soil profile and floristic communities in the hopes of adding to a thorough understanding of what once was to benefit what will be.
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