Characterizing methanogen and methanotroph diversity, abundance and activity within the Hampshire-Avon catchment

Methane (CH4) is an important greenhouse gas and research into its production and oxidation by microbial communities is crucial in predicting their impact in future climate change. Here, potential rate measurements, quantitative real-time polymerase chain reactions (Q-PCR) of pmoA, mcrA genes and next generation sequencing, were applied to characterize methanogen and methanotroph community structure, abundance and activity in the Hampshire-Avon catchment, UK. Soil and river sediments were taken from sites across different underlying geologies based on their baseflow index (BFI); from low (chalk) to medium (greensand) to high BFI (clay). In general, methane oxidation potentials (MOP) and methane production potentials (MPP) were greater in river sediments compared to soils (particularly higher in clays). Sequence analysis identified Methanococcoides, Methanosarcina and Methanocorpusculum as candidates driving methanogenesis across all river geologies. Methylocystis was also found to predominate in all the river sediments and may be a key methane oxidiser. In soils microcosms, MOP doubled when temperature was increased from 4oC to 30oC (in greensand soils sampled in summer but not winter). In long-term in-situ field warming experiments, MOP was unaffected by temperature in the clay and chalk soils, whereas MOP increased by two-fold in the greensand soils. In both microcosms and field warming experiments pmoA abundance was unchanged. In soil microcosms amended with nitrogen (N) and phosphate (P), high N and low P concentrations had the greatest inhibition on methane oxidation in clay soils, whilst chalk and greensand soils were unaffected. The pmoA gene abundance was also the highest in chalk soils (<2.98 x105 gene copies g-1 dry weight soil) and was unchanged across treatments. However, in the greensand and clay soils, pmoA gene abundance fluctuated with treatment. In long-term field N and P manipulations, regardless of treatment, clay soils had the highest MOP followed by chalk and Greensand. There was also a 10-fold increase in pmoA gene abundance across all treatments, and geology. The findings of this research demonstrated that CH4 production and oxidation in soils and sediments can be tied to different underlying geologies, with clay geologies having the highest CH4 production and oxidation. In addition, soil temperature changes are found to likely be secondary factors affecting methanotrophs, with MOP only increasing with temperature if CH4 is abundant. N and P additions to soils had an overall negative effects on methanotrophy in clay soils but an overall positive effect in chalk soils, and no effect on greensand soils. These results may enable more targeted catchment management strategies to be performed to mitigate future increases in CH4 concentrations.