Integrating the ecology of the soil microbiome into our understanding of bioproduct agroecosystem productivity and sustainability

Jenni Kane, Jeffrey G. Skousen, Louis McDonald and Ember Morrissey, Division of Plant and Soil Sciences, West Virginia University, Morgantown, WV, Zachary Freedman, Department of Soil Science, University of Wisconsin, Madison, WI

Background/Question/Methods
Optimizing how land is used for agriculture is critical, since food and energy production must increase alongside the growing population. Anthropogenically damaged land is often not an option for large-scale food production due to poor soil conditions leading to high input needs and low yield. However, utilizing these lands to grow robust bioproduct crops like Miscanthus × giganteus could help relieve competition for land while contributing to green energy production and enhanced soil fertility. Interactions between Miscanthus plants and the soil microbiome determine crop success and mediate the cycling and storage of nutrients. The Miscanthus microbiome is sensitive to environmental change; however, the influence of agricultural practices on these communities remains understudied. When systems are over-fertilized, microbial communities may shift toward lower nutrient use efficiency as fast-growing life strategies become favored. This may lead to consequences like nutrient runoff and poor crop quality or yield. To test this, an experiment was initiated in anthropogenically disturbed soils whereby Miscanthus plots were established and treated with one of four amendment treatments (low- and high-level inorganic, organic, control). The structure and function of the soil microbiome was assayed by sequencing gene amplicons and tracking carbon and nitrogen cycling using isotopically labeled substrate additions.
Results/Conclusions
After two years of Miscanthus production, the uptake of ammonium into microbial biomass decreased by ~30% in the high-inorganically amended plots and by ~20% in the low inorganically amended plots, but it did not significantly change in the organically amended plots relative to the control. Respiration was stimulated in the high-inorganically amended plots, increasing ~10% relative to the control. However, crop yield was not enhanced in fertilized plots. These results indicate that microbiome function is sensitive to land management practices in Miscanthus agroecosystems. However, the pulse of nutrients that comes with the high-inorganic amendment stimulates respiration but not nitrogen incorporation into microbial biomass or crop yield, resulting in overall losses of carbon and nitrogen from the system. Hence, we may be able to leverage microbiome structure and function through land management to decrease environmental impacts and restore soil fertility in agroecosystems without sacrificing crop yield.