Nitrogen Cycling Microbial Community Affected By Perennial Energy Crops on Riparian Buffer.

The relationship between nitrogen application and bioenergy crop production is well demonstrated through growth development and biomass yield. However, there is limited understanding of the interaction between soil microbial communities and bioenergy crops. The objective of this study was to determine the effects of perennial energy crop management practices, including species (switchgrass, prairie cordgrass, Miscanthus x giganteus, and a grass mixture), harvest timing (at anthesis and a after killing frost), and N-rate (0, 56, and 112 kg N ha^-1), on soil functional microbial communities involved in the nitrogen cycle on a riparian buffer. We investigated eight target genes of N cycling functional groups involved in ammonia oxidation (bacterial amoA, archaeal amoA), nitrite ammonification (nrfA), denitrification (nirK, nirS, norB, and nosZ), and nitrogen fixation (nifH). Overall, the results indicated that the interaction among N-rates, harvest timing, and species had significant effects on the abundance of microbial communities. The copy number of ammonia-oxidizing bacteria (B amoA) increased as N fertilization increased, thereby increasing the proportion of B amoA compared to archaeal amoA. Denitrifier (nirK) was also more abundant in the plot with 112 kg N ha^-1 applied. Delaying biomass harvest until after a killing frost increased populations of all tested N cycling microbes. Our data implies that management practices of perennial grasses, especially N application and harvest timing, could have significant impacts on changes in soil microbial communities within the rhizosphere.