Endogeic earthworms lower net methane production in saturated riparian soils

Abstract

Methane (CH₄) emissions from soils are erratic, the typical pattern being long periods of imperceptible emissions punctuated by short periods of high CH₄ release. These short peaks are a result of higher gross CH₄ production rates (methanogenesis) relative to gross rates of CH₄ consumption (methanotrophy), and can be induced by rising water table level and periodic flooding in riparian soils. Soil fauna, specifically earthworms, affected soil CH₄ cycling in some studies. We studied the effect of the endogeic earthworm Aporrectodea turgida (Eisen) on CH₄ production and consumption activities in saturated and field-moist soils collected from a riparian area in southern Québec, Canada. Saturated (100 % water-filled pore space, WFPS) and field-moist soils (31.5 % WFPS) were incubated at 20 °C, with difluoromethane added to quantify gross CH₄ production (i.e., methanogenesis activity) and consumption rates (i.e., methanogenic activity). The pattern of gross CH₄ consumption followed that of gross CH₄ production, and net CH₄ production was an order of magnitude lower than the gross rate. Gross rates of CH₄ production were 41 to 65 ng CH₄ g⁻¹ h⁻¹, gross CH₄ consumption rates were estimated to be 37 to 63 ng CH₄ g⁻¹ h⁻¹, and the net CH₄ production ranged from 2 to 4 ng CH₄ g⁻¹ h⁻¹. Saturated soils with earthworms had consistently lower net CH₄ production, relative to field-moist and saturated soils without earthworms. This means that earthworms could potentially reduce the impact of periodic flooding on CH₄ emissions from riparian soils.