VARIATIONS IN MICROBIAL-POPULATIONS IN SOILS WITH DIFFERENT METHANE UPTAKE RATES

The rate of methane oxidation has been measured from under a variety o f land uses and management practices on Rothamsted Experimental Statio n. 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 associa ted with land use, where the rate of methane oxidation in unfertilized arable soil (c. 30 mu g CH4 m(-2) d(-1)) is only 15 % that in undistu rbed grassland and woodland soils (c. 200 mu g CH4 m(-2) d(-1)). Inves tigation of the mechanisms regulating these differences have shown tha t they are microbially mediated. The microbial basis for differences i n methane uptake rates are unclear, but probably involve three groups of microorganism, methanogens, methanotrophs and ammonia oxidisers. Us ing traditional enumeration techniques we show that soils under grassl and and woodland have similar numbers of bacteria and also similar num bers of putative methane oxidisers (organisms of unknown identity, tha t can oxidise methane), but that an unfertilized arable soil has signi ficant lower total bacterial numbers and also putative methane oxidise rs. This study is extended to compare the capacities of the soils unde r the different land uses to metabolise multi-carbon compounds in addi tion to methane. Using a modification of the Biolog<reg> technique we demonstrate that the microbial populations in the soil under the woodl and and grassland can metabolise a greater range of carbon compounds c ompared to the arable soil, as well as having higher methane oxidising capabilities.