Drivers of Plot-Scale Variability of CH4 Consumption in a Well-Aerated Pine Forest Soil

Abstract

While differences in greenhouse gas (GHG) fluxes between ecosystems can be explained to a certain degree, variability of the same at the plot scale is still challenging. We investigated the spatial variability in soil-atmosphere fluxes of carbon dioxide (CO 2 ), methane (CH 4 ) and nitrous oxide (N 2 O) to find out what drives spatial variability on the plot scale. Measurements were carried out in a Scots pine (Pinus sylvestris L.) forest in a former floodplain on a 250 m 2 plot, divided in homogenous strata of vegetation and soil texture. Soil gas fluxes were measured consecutively at 60 points along transects to cover the spatial variability. One permanent chamber was measured repeatedly to monitor temporal changes to soil gas fluxes. The observed patterns at this control chamber were used to standardize the gas fluxes to disentangle temporal variability from the spatial variability of measured GHG fluxes. Concurrent measurements of soil gas diffusivity allowed deriving in situ methanotrophic activity from the CH 4 flux measurements. The soil emitted CO 2 and consumed CH 4 and N 2 O. Significantly different fluxes of CH 4 and CO 2 were found for the different soil-vegetation strata, but not for N 2 O. Soil CH 4 consumption increased with soil gas diffusivity within similar strata supporting the hypothesis that CH 4 consumption by soils is limited by the supply with atmospheric CH 4 . Methane consumption in the vegetation strata with dominant silty texture was higher at a given soil gas diffusivity than in the strata with sandy texture. The same pattern was observed for methanotrophic activity, indicating better habitats for methantrophs in silt. Methane consumption increased with soil respiration in all strata. Similarly, methanotrophic activity increased with soil respiration when the individual measurement locations were categorized into silt and sand based on the dominant soil texture, irrespective of the vegetation stratum. Thus, we suggest the rhizosphere and decomposing organic litter might represent or facilitate a preferred habitat for methanotrophic microbes, since rhizosphere and decomposing organic are the source of most of the soil respiration.

Above- and belowground fluxes of methane from boreal dwarf shrubs and Pinus sylvestris seedlings

“…The results also show some variation in both the belowground CH4 fluxes and the amount of methanotrophs between the species, V. vitis-idaea-rooted-soils indicating the strongest uptake. The effect of plant species and vegetation types on soil CH4 fluxes has also been shown by other studies (Praeg et al 2016;Maier et al 2017b). These differences can result from the different plant species effects on soil microbes, which may again result from the root exudates (Innes et al 2004).…”

Automated measurements of greenhouse gases fluxes from tree stems and soils: magnitudes, patterns and drivers

“…Under low soil moisture conditions, we would expect low transpiration and thus, less stem CH 4 emissions, but also high soil diffusivity resulting in higher diffusion of atmospheric CH 4 and O 2 into the soil, and consequently more soil CH 4 consumption. On the other hand, high SWC would enhance transpiration, resulting in higher sap flux and high stem emissions but it would also cause a reduction of soil diffusivity, then a reduction in soil oxygenation and CH 4 diffusion from the atmosphere and consequently a reduction of CH 4 soil uptake 58,59 .…”

From above the forest into the soil – How wind affects soil gas transport through air pressure fluctuations

“…Soil aeration controls the supply of oxygen in the soil and allows aerobic or anaerobic conditions, on which other soil processes like denitrification and methane production are coupled. Moreover, the oxidation of CH4 in upland forests is assumed to be controlled by the supply rate of CH4 and O2 from the atmosphere to methanotrophic bacteria located in the topsoil (Maier et al, 2017b;Smith et al, 2000). Increasing gas transport by PPE could potentially increase the CH4 consumption.…”