The Prairie Underground: Soil Recovery in Chicago Wilderness Restoration

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The tallgrass prairie once dominated much of the mid-western United States. Today, this highly productive system has been severely reduced, contributing to an array of environmental problems. The recent renaissance in natural area restoration and stewardship of the tallgrass prairie in the Chicago Wilderness region (Illinois, USA), especially in the efforts to restore former agricultural fields to tallgrass prairie, offer a valuable opportunity to assess the generality of changes in soil ecosystem-level processes in managed grassland systems. In this study, I examine the changes in the abundance of fungi relative to bacteria (F: B, by qPCR) and physical and chemical factors (texture, aggregate structure, acidity, soil organic matter (SOM), nitrogen (N) and phosphorous (P) fertility) in soils collected from prairie restorations of varying ages, as well as abandoned fields and undisturbed native prairie remnants. I used these data to ask whether shifts in microbial abundance and community structure occur within aggrading soil systems, and how these shifts might be related to other soil factors. More specifically, Ipredicted that the abundance of fungi relative to bacteria should increase following conversion from tillage agriculture to tallgrass prairie, and continue to increase with increases in SOM over the management period. If so, the detection of a substantial increase in microbial biomass and F: B could be used to indicate effective restoration progress, or reflect changes in other indicators of soil function. My results demonstrate that F: B were lower in abandoned fields than in restored sites, and that F:B was related to soil fertility and other edaphic properties. These data support my prediction, and indicate that management on a regional scale promotes a shift in microbial community structure. This finding is important because it suggests that fungi play an increasingly significant role in soil biological processes of managed and restored grasslands. Further, the observed shifts in F: B were correlated with decreasing soil fertility (N) and changes in other edaphic properties, such as silt and pH. The shift in F: B was not substantially correlated with soil aggregation, clay, or P. While these results support my predictions, they also suggest that changes in abiotic soil properties may be a prerequisite for increases in fungal biomass toward levels found in pristine prairie remnants. Overall, these findings lay an important foundation for understanding tallgrass prairie restoration and management in that: deficits in the microbial community structure resulting from intensive agriculture may be reversible; restoration management may facilitate the shift to a fungal-based soil food web; and F: B ratios provide a valuable integrative measure of system development and maturity.

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  • 02/01/2019
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