Rhizosphere activity and atmospheric methane concentrations drive variations of methane fluxes in a temperate forest soil

Catherine S. Moody,Timothy C. Hill,Yit Arn Teh,Philip Ineson,Sylvia Toet,Naomi Voke,Jens-Arne Subke

doi:10.1016/j.soilbio.2017.10.037

Abstract

Aerated soils represent an important sink for atmospheric methane (CH4), due to the effect of methanotrophic bacteria, thus mitigating current atmospheric CH4 increases. Whilst rates of CH4 oxidation have been linked to types of vegetation cover, there has been no systematic investigation of the interaction between plants and soil in relation to the strength of the soil CH4 sink. We used quasi-continuous automated chamber measurements of soil CH4 and CO2 flux from soil collar treatments that selectively include root and ectomycorrhizal (ECM) mycelium to investigate the role of rhizosphere activity as well as the effects of other environmental drivers on CH4 uptake in a temperate coniferous forest soil. We also assessed the potential impact of measurement bias from sporadic chamber measurements in altering estimates of soil CO2 efflux and CH4 uptake. Results show a clear effect of the presence of live roots and ECM mycelium on soil CO2 efflux and CH4 uptake. The presence of ECM hyphae alone (without plant roots) showed intermediate fluxes of both CO2 and CH4 relative to soils that either contained roots and ECM mycelium, or soil lacking root- and ECM mycelium. Regression analysis confirmed a significant influence of soil moisture as well as temperature on flux dynamics of both CH4 and CO2 flux. We further found a surprising increase in soil CH4 uptake during the night, and discuss diurnal fluctuations in atmospheric CH4 (with higher concentrations during stable atmospheric conditions at night) as a potential driver of CH4 oxidation rates. Using the high temporal resolution of our data set, we show that low-frequency sampling results in systematic bias of up-scaled flux estimates, resulting in under-estimates of up to 20% at our study site, due to fluctuations in flux dynamics on diurnal as well as longer time scales.

Highlights

Biogenic trace gases such as carbon dioxide (CO2) and methane (CH4) play a pivotal role in global climate change (Ciais et al, 2013; Tian et al, 2016)
Methane oxidation in upland soils represent an important sink for atmospheric CH4, but poor constraints on the uptake of atmospheric CH4 by soil microorganisms contributes to overall uncertainty in the global atmospheric CH4 budget, and predictions of how soil-atmosphere feedbacks may modulate future changes in atmospheric CH4 concentrations (Kirschke et al, 2013; Nisbet et al, 2014)
Cumulative flux sums were analysed by means of a two-way Analysis of Variance (ANOVA) for each chamber to look for a block and treatment effect, and a post-hoc Duncan's MRT test applied, if the data met the assumptions of homogeneity of variance and normality

Summary

Introduction

Biogenic trace gases such as carbon dioxide (CO2) and methane (CH4) play a pivotal role in global climate change (Ciais et al, 2013; Tian et al, 2016). Driven increases in atmospheric CO2 from fossil fuel combustion and land-use change are the main drivers of climate change. Increasing atmospheric CH4 concentrations are thought to contribute 20% of the total greenhouse gas warming (Ciais et al, 2013; Myhre et al, 2013). Methane oxidation in upland soils represent an important sink for atmospheric CH4, but poor constraints on the uptake of atmospheric CH4 by soil microorganisms contributes to overall uncertainty in the global atmospheric CH4 budget, and predictions of how soil-atmosphere feedbacks may modulate future changes in atmospheric CH4 concentrations (Kirschke et al, 2013; Nisbet et al, 2014). Whilst the dynamics and drivers of CO2 exchange from terrestrial ecosystems are reasonably well understood (Jung et al, 2011), there remain significant uncertainties around feedbacks between plants, soil microbes, and the potential role of rhizosphere priming effects (Talbot et al, 2013)

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