Above- and belowground biomass and soil respiration in a low-input perennial biofuel production system

Background/Question/Methods

Corn grain ethanol production results in high levels of CO₂ emissions and agricultural pollution, but cellulosic ethanol from low-input perennial crops could reduce some of these negative impacts and sequester carbon belowground. A production-scale biomass research site was established in 2009 at the University of Northern Iowa to investigate the potential mitigation of these consequences through the use of various mixes of native prairie vegetation harvested from marginal agricultural lands. Plots were seeded with one of four diversity treatments: (1) 1 species – a switchgrass monoculture, (2) 5 species – a mix of warm-season grasses, (3) 16 species – a mix of grasses, legumes and forbs, or (4) 32 species – a mix of grasses, sedges, legumes and forbs. Each treatment was replicated four times on three different soil types for a total of 48 experimental plots. In this study, we measured aboveground biomass, belowground biomass, and soil respiration to quantify the effects of plant diversity and soil type on productivity, CO₂ flux and soil C sequestration. 

Results/Conclusions

Aboveground biomass production differed significantly between diversity levels and between soil types (p < 0.05). In addition, the diversity treatment that achieved the highest aboveground biomass varied between soil types (p < 0.05). Differences in belowground biomass and soil respiration rates paralleled the patterns observed for aboveground biomass. Our results suggest that the use of native prairie vegetation for cellulosic biofuels can result in substantial belowground carbon sequestration which may help mitigate carbon emissions while still producing sufficient biomass for economically-viable biofuel harvest. Differences in the relative ranking of the diversity treatments between soil types suggests that soil properties ought to be considered when selecting a seed mix for bioenergy to maximize yield and ecosystem services. Future research should also consider the effects of diversity and soil type on related ecological processes such as litter decomposition and root formation. Knowledge of these types of responses will expand our understanding of the ecological impacts of harvest-scale biofuel production and the environmental implications of using native prairie vegetation.