Microbial community PLFA and PHB responses to ecosystem restoration in tallgrass prairie soils

Native North American prairie grasslands are renowned for the richness of their soils, having excellent soil structure and very high organic content and microbial biomass. In this study, surface soils from three prairie restorations of varying ages and plant community compositions were compared with a nearby undisturbed native prairie remnant and a cropped agricultural field in terms of soil physical, chemical and microbial properties. Soil moisture, organic matter, total carbon, total nitrogen, total sulfur, C:N, water-holding capacity and microbial biomass (total PLFA) were significantly greater (p<0.05) in the virgin prairie remnant as well as the two long-term (21 and 24 year) prairie restorations, compared with the agricultural field and the restoration that was begun more recently (7 years prior to sampling). Soil bulk density was significantly greater (p<0.05) in the agricultural and recently restored sites. In most cases, the soil quality indicators and microbial community structures in the restoration sites were intermediate between those of the virgin prairie and the agricultural sites. Levels of poly-β-hydroxybutyrate (PHB) and PLFA indicators of nutritional stress were significantly greater (p<0.05) in the agricultural and recent restoration sites than in the long-term restorations or the native prairie. Samples could be assigned to the correct site by discriminant analysis of the PLFA data, with the exception that the two long-term restoration sites overlapped. Redundancy analysis showed that prairie age (p<0.005) was the most important environmental factor in determining the PLFA microbial community composition, with C:N (p<0.015) also being significant. These findings demonstrate that prairie restorations can lead to improved quality of surface soils. We predict that the conversion of farmland into prairie will shift the soil quality, microbial community biomass and microbial community composition in the direction of native prairies, but with the restoration methods tested it may take many decades to approach the levels found in a virgin prairie throughout the soil profile.