Toward belowground restoration: understanding the effects of land management on soil microbial processes in a tallgrass prairie
Agricultural cultivation in the Midwestern United States has caused an 82-99% decline in the tallgrass ecosystems that once dominated North America and has severely impacted the ecosystem services they provide. Current prairie restoration and land management approaches focus on improving aboveground ecosystems, but are poorly integrated with restoration of soil microbial biodiversity and carbon cycling. Restored prairies harbor microbial communities that metabolize more labile forms of carbon and have greater rates of soil respiration than pristine remnant prairies, suggesting that traditional prescribed burn approaches lead to an alternative stable belowground community. In this study, we examined the impact of a prescribed fire over the course of one year, in a chronosequence of remnant and restored tallgrass prairies located in southwest Michigan. In addition to characterizing the plant community and soil abiotic characteristics, we examined16S rRNA-based soil microbial biodiversity, extracellular enzyme activities of B-glucosidase, cellobiohydrolase, N-acetylglucosaminidase and phosphatase and microbial utilization of 31 carbon substrates using a Biolog Ecoplate approach.
Prior to implementing a prescribed burn, soil nitrate, ammonium and total phosphorus concentrations were significantly higher in restored prairies than in the remnant (p < 0.01). Soil microbial carbon utilization (p = 0.046) and 16S rRNA Bacterial diversity (p = 0.03) also differed between restored and remnant prairies. Taxa in the restored prairies preferentially utilized labile carbon compounds that contained nitrogen, while taxa in the remnant prairies used higher molecular weight carbon compounds. In addition, phosphatase and cellobiohydrolase enzyme activities were higher in the remnant prairie than in the restored prairies (p < 0.04), but B-glucosidase and N-acetylglucosaminidase activities did not differ (p > 0.07). Prescribed fire had a homogenizing effect on soil microbial carbon utilization and enzyme activities, increasing the similarity between restored and remnant prairies in the time series following the fire. Burning did not influence microbial diversity, and the differences we observed pre-fire between the prairies returned one year following the fire. This suggests that low-temperature prescribed fires have an immediate effect on microbial activity, but that the effect does not lead to long-term restoration of microbial biodiversity and function.