Monocultures and diverse mixtures of perennial bioenergy crops are being considered for sustainable energy feedstocks, and diverse mixtures offer additional value by increasing species diversity and providing wildlife habitat. Perennial cropping systems are known to enhance ecosystem services relative to annual crops; however, the difference in services provided by perennial monocultures versus diverse species mixtures is not yet well understood. We investigated belowground ecosystem effects of a monoculture of switchgrass (Panicum virgatum) and a diverse mixture of native grassland species established on erodible agricultural land in SW Wisconsin, USA. These crops were established in 2008 and received a treatment of prescribed fire or no fire in 2009. We estimated the effects of species diversity and prescribed fire on N availability, net mineralization rate, and soil respiration in May, July and September 2010. We also measured activities of 8 microbial exoenzymes in September 2010.
Preliminary analyses indicate that species composition and burning did not affect N availability and net mineralization rates. N availability was greatest and net mineralization rate was lowest in July, relative to May and September. Soil respiration in was increased by fire in the monoculture and decreased by fire in the diverse mixture in July, and the opposite trend was observed in September. Soil respiration decreased over time in the burned monoculture and unburned diverse mixture. Analyses of microbial exoenzyme activities will be presented. Together, the processes we evaluated elucidate the effects of plant species diversity and fire on overall resource availability and nutrient cycling across a growing season. These results will help evaluate the effects of alternative bioenergy crops on ecosystem function.