Soil Microbial Community Response to Climate Change: Results From a Temperate Kentucky Pasture.

Soil microbial communities play a critical role in maintaining some ecosystem services provided by pastures, including determining carbon sequestration rates and plant nutrient availability.  Soil microbes are sensitive to abiotic conditions and substrate availability, and are therefore likely to be both directly and indirectly impacted by climate change through altered temperature and precipitation dynamics and also through plant community response to these changes and resulting feedbacks to the soil microbial community. This study assessed the seasonal dynamics of soil microbes and their response to increased temperature (+3^oC) and growing season precipitation (+30% of the mean annual) in a pasture of central Kentucky. Total soil microbial biomass, community composition, enzyme activities, potential carbon mineralization, and catabolic responses to selected substrates were measured seasonally in the different climate treatments.

Surprisingly, given the dramatic response of the plant community, climate treatments produced few significant effects on the soil microbial biomass and function: warming treatments increased microbial biomass carbon and catabolic response to sucrose and cellulose compared to the other climate treatments. Results illustrated that, in this system, seasonal variability is a dominant driving factor for all the soil microbial characteristics that were investigated.  Summer maxima and winter minima were identified in microbial lipid biomass, while soil microbial community structure differed between each season. Extracellular enzyme activities were generally highest in either the spring or summer, while seasonal patterns for each substrate were unique across catabolic response profiles. The limited response to climate treatments suggests that the soil microbial community in this central Kentucky pasture may be well-equipped to handle future environmental conditions and will maintain critical ecosystem services.