The influence of plants on atmospheric methane in an agriculture-dominated landscape

The primary objective of this study was to clarify the influence of crop plants on atmospheric methane (CH₄) in an agriculture-dominated landscape in the Upper Midwest of the United States. Measurements were carried out at two contrasting scales. At the plant scale, CH₄ fluxes from soybean and corn plants were measured with a laser-based plant chamber system. At the landscape scale, the land surface flux was estimated with a modified Bowen ratio technique using measurements made on a tall tower. The chamber data revealed a diurnal pattern for the plant CH₄ flux: it was positive (an emission rate of 0.4 ± 0.1 nmol m^-2 s^-1, average of soybean and corn, in reference to the unit ground area) during the day, and negative (an uptake rate of -0.8 ± 0.8 nmol m^-2 s^-1) during the night. At the landscape scale, the flux was estimated to be 14.8 nmol m^-2 s^-1 at night and highly uncertain during the day, but the available references and the flux estimates from the equilibrium methods suggested that the CH₄ flux during the entire observation period was similar to the estimated nighttime flux. Thus, soybean and corn plants have a negligible role in the landscape-scale CH₄ budget.