Carbon dynamics of temperate savannas: Effects on prescribed fire on microbial activity and potential carbon mineralization. Hollister, Emily^*,1, Boutton, Thomas¹, Ansley, R. James², ¹ Texas A&M University, College Station, TX² Texas Agricultural Experiment Station, Vernon, TX

ABSTRACT- Land uses and land cover changes frequently alter key ecosystem processes, such as productivity and decomposition, and influence the magnitude and direction of ecosystem nutrient fluxes. In the southern Great Plains, prescribed burning is often used in the management grasslands that have been invaded by mesquite (Prosopis glandulosa). As part of a broader effort to understand the effects of prescribed fire on ecosystem carbon dynamics we quantified soil microbial biomass (SMB) and potential carbon mineralization (CM) rates in soils collected monthly beneath grass vs. woody vegetation in 3 long-term fire treatments (controls, winter fire, and summer fire). SMB ranged from 511 mg C kg^-1 soil in the controls to 897 mg C kg^-1 soil in the summer fire treatment and was controlled by significant (p < 0.01) interaction among vegetation type, fire, and season in all treatments. SMB in all fire × vegetation combinations generally peaked in autumn and was lowest in spring. Conversely, rates of potential CM experienced significant interaction (p < 0.05) between fire treatment and vegetation type and peaked in mid-summer. Trends of long-term CM showed similar patterns of CO₂ release across all treatments, with soils from the summer fire treatment having lower respiration rates than those from all other treatments after 272 days of incubation. These differences were significant between the summer and winter fire treatments (p <0.05). Results indicate that fire and vegetation type exert important controls over the magnitude and activity of SMB pools and have potential implications for ecosystem carbon storage.

KEY WORDS: prescribed fire, soil microbial biomass, potential carbon mineralization, carbon cycle