Indirect microbial effects on methane flux are stronger when the environmental influence is weaker in a temperate forest ecosystem

Microbial gene markers are hypothesized to be mediating factors between environment factors and methane flux, but mediation is not typically modeled directly in ecosystem studies using graphic models. Structural equation modelling (SEM) was used to test if mcrA and 16S markers were mediating the effects of soil moisture on methane flux in two ecosystem types, Upland and Wetland Forest. SEM results indicated that mcrA functional marker was a mediator in the Upland Forest but not in the Wetland Forest. In the Upland Forest, the 16S marker indirectly effected methane flux though its effect on the mcrA marker. The results suggest that functional genes are mediating drivers in ecosystems where environmental factors are weak drivers of methane fluxes. Our results highlight the importance of testing for microbial indirect pathways in assessing drivers of methane cycling and provide a basis for more complex modelling of mediated pathways in analysis of ecosystem processes.