Variations in microbial populations in soils with different methane uptake rates

The rate of methane oxidation has been measured from under a variety of land uses and management practices on Rothamsted Experimental Station. All these sites have their management histories well documented, in many cases over centuries, and experience the same atmospheric inputs. We have found consistent patterns in methane oxidation rates associated with land use, where the rate of methane oxidation in unfertilized arable soil (c. 30 µg CH₄ m^-2 d^-1) is only 15 % that in undisturbed grassland and woodland soils (c. 200 µg CH₄ m^-2 d^-1). Investigation of the mechanisms regulating these differences have shown that they are microbially mediated. The microbial basis for differences in methane uptake rates are unclear, but probably involve three groups of microorganism, methanogens, methanotrophs and ammonia oxidisers. Using traditional enumeration techniques we show that soils under grassland and woodland have similar numbers of bacteria and also similar numbers of putative methane oxidisers (organisms of unknown identity, that can oxidise methane), but that an unfertilized arable soil has significant lower total bacterial numbers and also putative methane oxidisers. This study is extended to compare the capacities of the soils under the different land uses to metabolise multi-carbon compounds in addition to methane. Using a modification of the Biolog technique we demonstrate that the microbial populations in the soil under the woodland and grassland can metabolise a greater range of carbon compounds compared to the arable soil, as well as having higher methane oxidising capabilities.