Abstract

Soil-to-atmosphere methane (CH4) fluxes are dependent on opposing microbial processes of production and consumption. Here we use a soil–vegetation gradient in an Australian sub-alpine ecosystem to examine links between composition of soil microbial communities, and the fluxes of greenhouse gases they regulate. For each soil/vegetation type (forest, grassland, and bog), we measured carbon dioxide (CO2) and CH4 fluxes and their production/consumption at 5 cm intervals to a depth of 30 cm. All soils were sources of CO2, ranging from 49 to 93 mg CO2 m−2 h−1. Forest soils were strong net sinks for CH4, at rates of up to −413 µg CH4 m−2 h−1. Grassland soils varied, with some soils acting as sources and some as sinks, but overall averaged −97 µg CH4 m−2 h−1. Bog soils were net sources of CH4 (+340 µg CH4 m−2 h−1). Methanotrophs were dominated by USCα in forest and grassland soils, and Candidatus Methylomirabilis in the bog soils. Methylocystis were also detected at relatively low abundance in all soils. Our study suggests that there is a disproportionately large contribution of these ecosystems to the global soil CH4 sink, which highlights our dependence on soil ecosystem services in remote locations driven by unique populations of soil microbes. It is paramount to explore and understand these remote, hard-to-reach ecosystems to better understand biogeochemical cycles that underpin global sustainability.

Highlights

  • Counteracting biogeochemical processes that consume or produce greenhouse gases (GHGs) regulates whether soils act as net sources or sinks

  • We developed a model to estimate annual CH4 production across the Australian Alps based on a number of geographic information system (GIS) datasets

  • Gravimetric water content on 17 February ranged from 0.25 to 0.79 for forest soils, 0.25–0.38 for grassland soils, and 0.9–4.66 g H2 O g dry soil−1 for bog soils (Table S4)

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Summary

Introduction

Counteracting biogeochemical processes that consume or produce greenhouse gases (GHGs) regulates whether soils act as net sources or sinks. Soils can routinely be either sources or sinks for methane (CH4 ). Soils can switch from being a net source to a net sink for CH4 in a matter of minutes to hours [8,9,10]. Lateral distances of less than a meter may be enough for a soil to switch from a sink to a source of GHGs or vice versa [11,12,13]

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