San Diego State University, California, United States
Abstract: Background/Questions/Methods
It has been proposed that mesic grasslands have greater carbon sink potential compared to xeric grasslands. Woody plant encroachment and land management practices are factors that may significantly impact microbial carbon cycling processes in mesic grasslands. Even though encroachment of trees and shrubs leads to increases in soil organic inputs of structurally complex litter, some studies have found that woody-derived carbon accumulates primarily in rapidly cycling and physically unprotected soil fractions. Additionally, the majority of findings on woody encroachment into grasslands has accumulated from xeric systems, so relatively little is known about how this ecological phenomenon plays out in mesic grasslands. Mesic grasslands, such as those that once dominated the Upper Midwest of the United States, have also been heavily impacted by agricultural disturbance. Today this landscape consists of small patches of remnant prairie and restoration prairies that were formerly used for agriculture. The objective of this study was to investigate how land management practices and woody encroachment influences microbial carbon cycling dynamics in a mesic temperate grassland. We performed amplicon sequencing and conducted extracellular enzyme assays on soils collected from a remnant prairie and an adjacent restoration prairie in the prairie-forest border region of southern Wisconsin to address the following hypotheses: 1) Remnant soils will contain more copiotrophic microbial taxa and will yield faster C degradation rates than restoration soils; 2) the relative abundance of copiotrophic taxa will increase with woody encroachment, which will stimulate higher C degradation rates relative to unencroached soils.
Results/Conclusions
We found that land management and woody encroachment substantially influenced both microbial community composition and extracellular enzyme activity. Contrary to our land management hypothesis, remnant prairie soils contained lower relative abundance of copiotrophic taxa compared to restoration prairie soils. Degradation rates of glucose and chitin were slightly higher in remnant soils compared to restoration soils. In support of our woody encroachment hypothesis, copiotrophic taxa were more abundant in encroached soils compared to unencroached soils. In addition, degradation rates of multiple carbon substrates were significantly higher in encroached soils compared to unencroached soils.
