Effect of Earthworms On Methane Flux In Temperate Pastures.

Methane, a potent greenhouse gas, is produced or consumed by microorganisms in soil depending on soil conditions.  In general, anaerobic conditions promote activity of methane-producing (methanogenic) Archaea, whereas aerobic conditions promote methane consumption by methanotrophic bacteria.  Earthworms may have an effect on methane flux in soil by altering soil pore space, aeration, moisture content, and organic carbon availability, all of which affect activities of methanogens and methanotrophs.  As the range of earthworms expands, their potential effects on methane flux may have global implications.  We focused on effects of earthworms on methane flux in a temperate pasture field and on potential mechanisms involved.  In November, 2009, we established 24 experimental plots at Peckham Farm, Kingston, and W. Alton Jones, West Greenwich, both in southern Rhode Island.   Three treatments (n=8) were implemented: (i) earthworms removed, (ii) earthworms removed, counted and returned to the plot, and (iii) undisturbed.  Plots were fitted with closed chamber gas collectors.  Weekly methane flux measurements were started in April, 2010 and will be made until November, 2010.  In addition, soil moisture and temperature are continually recorded and relevant soil chemical and physical properties determined periodically.  Samples from cast, burrow, and bulk soil will be analyzed to determine rates of methanogenesis and methane oxidation.  This will allow examination of mechanisms by which earthworms affect methane flux in the field.  Preliminary results for data from April 15, 2010 to July 1, 2010 show both sites on all sampling days to be net consumers of methane, with flux values ranging from -18.0 to -99.5 ng/m²/sec.  The Peckham Farm site shows no significant differences in methane flux relative to earthworm treatment (p=0.0374).  However, the W. Alton Jones site shows significantly lower net methane consumption for the earthworm treatment (p<0.001), suggesting that the presence of earthworms affects net consumption of methane in soil.