Print PageIntroduction of new crops to agro-ecosystems can change the composition of the atmosphere by altering the bouquet of plant-derived biogenic organic volatile compounds (BVOCs). BVOCs are low molecular weight secondary metabolites that are used by plants for defense, pollination and communication. They also influence the chemical and physical constituents of the atmosphere as potential greenhouse gases and precursors of particulate matter. In this study, we compared BVOC emissions from three potential biofuel crops, Miscanthus (Miscanthus x giganteus), switchgrass (Panicum virgatum) and native prairie grasses (mix of ~28 species) and estimated their potential impacts on bioenergy agro-ecosystems.
Closed volatile collection chambers were used to eliminate soil and farm machinery volatiles. In addition, volatiles were collected at four different heights within the canopy of each species and also at two different heights above the canopies. The measurements above the vegetation were used to calculate vertical fluxes of BVOCs using the flux-gradient method. All volatiles were analyzed by gas chromatography-mass spectrometry. Auxiliary data included air temperature, vapor pressure deficit, photosynthetically active radiation, wind speed and COfluxes from an eddy covariance system.
Results/Conclusions
More than 30 compounds were isolated from each plant in closed chambers. The pattern of emission within each plant canopy differed among plant species [F3,48=14.998, p<0.05]. Miscanthus produced a uniform emission level across the canopy while switchgrass and native prairie grasses produced higher levels of emissions at the upper canopy. We found significant differences in the chemical composition of volatiles across plant canopies in all three plants [F30,288= 2.408, p<0.05]. BVOCs from Miscanthus were depleted in terpenoids relative to the other vegetation types.
The carbon flux via BVOC emission in the native prairie grasses was significantly higher than miscanthus and switchgrass [F2,26=8.035, p<0.05]. Environmental factors were not significantly correlated with the BVOC fluxes.
Although the BVOC carbon fluxes of miscanthus and switchgrass were not significantly different [p>0.05 (0.954)], measurements of net ecosystem exchange indicated that miscanthus was a stronger carbon sink than switchgrass or native prairie grasses [F2,12=30.732, p<0.05]. Extrapolation of our findings to the landscape scale leads us to suggest that the widespread adoption of biofuel crops can potentially alter the composition of BVOCs in the atmosphere, thereby influencing its warming potential, the formation of atmospheric particulates and interactions between plants and arthropods.
