MICROBIAL BIOMASS DYNAMICS IN TALLGRASS PRAIRIE

The temporal dynamics and effects of burning, mowing, and N fertilizat ion on microbial biomass (MBM) in tallgrass prairie were studied in a field experiment established in 1986. Microbial C (MC) and microbial N (MN), determined by the fumigation-incubation procedure during the gr owing seasons of 1989 through 1991, averaged 217 mg C kg-1 and 32.6 mg N kg-1, respectively, for the 0- to 30-cm depth. Accumulation of litt er and greater production of roots near the surface resulted in strati fication of MBM. Seasonally, MBM was higher in early spring, decreased with the initiation of plant growth, and then recovered by late summe r or early fall. Decreases of MN between March and July coincided with plant N uptake. The increase of MC and decrease of MN during the 3 yr of the study were related to increased plant production. Burning had a short-term and variable effect on MC. Burning tended to reduce MC du ring dry years and increase it in normal to wet years. Mowing and raki ng decreased MC and MN, probably because of reduced root biomass and r emoval of standing vegetation. Nitrogen addition resulted in higher MN and tended to reduce MC, possibly by modifying the composition of the microbial population. Microbial biomass seems to play a critical role in conserving N in the tallgrass prairie ecosystem.