Soil microbial communities in grasslands: Spatial and temporal patterns at the local scale

Background/Question/Methods

Land-use intensity and seasonal plant-growth changes can modify both spatial distributions and functions of soil microorganisms. Previous studies from grasslands in southwest Germany have indicated strong spatial dependence of microbiological properties with high plant species diversity. Geostatistical analyses of soil biogeochemical properties, together with microbial biomass and enzymes involved in nutrient cycling, indicated spatial relationships at multiple scales. Temporal variability in these same parameters, however, was not explored. To address this gap, one low land use intensity grassland in the same region was selected to characterize how changes in the distribution of plant communities and substrate quality throughout a growing season changed the biogeography of soil microorganisms at the plot scale (10×10 m). Sixty samples/date were collected and analyzed six times over one growing season; at five plant growth stages, and once after frost-induced plant dormancy (360 total samples in a grid pattern). Belowground samples were analyzed for physical, chemical, and biological soil parameters, archaeal, bacterial, and fungal abundances, extracellular enzymes produced by microorganisms to exploit available plant-produced substrates, and microbial communities involved in nitrogen cycling. Aboveground samples were analyzed for plant and litter biomass, plant community composition, and species diversity. 

Results/Conclusions

Analysis of temporal changes indicated significant differences among most measured biological parameters between sampling dates. Geostatistical analyses of spatial heterogeneity of below-ground biological parameters also indicated changes with season. Plant functional group succession (grasses and forbs early, legumes and mosses late) correlated strongly and in some cases inversely with bacterial and fungal PLFAs both spatially and temporally. Additionally, both spatial patterns and abundances of microbial parameters showed strong spatial and temporal relationships to aboveground processes. Mean differences between dates often did not reflect observed spatial shifts in belowground parameters, however, indicating that both temporal and spatial approaches are needed to accurately characterize interactions between above- and below-ground processes in low land use intensity grasslands. This further suggests that changes in land use may influence belowground microbial communities in ways not yet understood.