Sustainable nitrogen cycling processes in the rhizosphere of perennial energy crops: N acquisition and retention

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Danyang Duan and Angela Kent, Natural Resources & Environmental Sciences, University of Illinois at Urbana-Champaign, Urbana, IL, Danyang Duan, Di Liang, Niuniu Ji and Angela Kent, DOE Center for Advanced Bioenergy & Bioproducts Innovation, University of Illinois at Urbana-Champaign, Urbana, IL

Background/Question/Methods

Warm-season grasses such as switchgrasses and miscanthus are ideal bioenergy feedstocks because of the high productivity with low levels of N inputs. Little to no N responses in miscanthus and switchgrass have been recorded previously, and a number of lines of evidence suggest that biological N fixation could be an N source. In addition, while the capacity for N retention derived from nitrification inhibition occurs in sorghum, a close relative of Miscanthus, little work has been done to evaluate the capacity of biological nitrification inhibition in other biofuel crops. To elucidate the N sustainability of bioenergy crops, nitrification and N fixation rates were tested in rhizosphere and bulk soils of different grass species: switchgrass (Panicum virgatum), prairie cordgrass (Spartina pectinata), a grass mixture (big bluestem, Indiangrass and side-oats grama), and four genotypes of miscanthus (‘Miscanthus x giganteus’, ‘Illinois’, ‘12UI-002-008’ and ‘64-1’). We also investigated the microbiome of different grass species by 16S rRNA sequencing, and the recruitment of nitrifiers and diazotrophs by sequencing N cycling marker genes (amoA and nifH).


Results/Conclusions

Despite the high variability of nitrification potentials in bulk soils, strong control of the host plants over the rhizosphere N cycling processes was displayed. The potential nitrification rates in rhizosphere soils were generally lower than bulk soil for all grass species. Specifically, the relative abundance of nitrifier taxa is the highest in cordgrass, followed by switchgrass, prairie mixture and miscanthus. In addition, there were no significant differences in N fixation measured among miscanthus genotypes. Results of microbial community structure revealed Nitrososphaera as the most abundant nitrifiers, and the dominant genera in miscanthus rhizosphere diazotroph assemblage included Rhodoplanes, Hyphomicrobium, Geobacter, Anaeromyxobacter and Bradyrhizobium. Overall, miscanthus ‘Illinois’ showed the best N sustainability with the highest rates of N fixation and nitrification suppression.