Widespread production of nonmicrobial greenhouse gases in soils

Abstract

Carbon dioxide (CO ), methane (CH ), and nitrous oxide (N O) are the three most important greenhouse gases (GHGs), and all show large uncertainties in their atmospheric budgets. Soils of natural and managed ecosystems play an extremely important role in modulating their atmospheric abundance. Mechanisms underlying the exchange of these GHGs at the soil-atmosphere interface are often assumed to be exclusively microbe-mediated (M-GHGs). We argue that it is a widespread phenomenon for soil systems to produce GHGs through nonmicrobial pathways (NM-GHGs) based on a review of the available evidence accumulated over the past half century. We find that five categories of mechanistic process, including photodegradation, thermal degradation, reactive oxidative species (ROS) oxidation, extracellular oxidative metabolism (EXOMET), and inorganic chemical reactions, can be identified as accounting for their production. These pathways are intricately coupled among themselves and with M-GHGs production and are subject to strong influences from regional and global change agents including, among others, climate warming, solar radiation, and alterations of atmospheric components. Preliminary estimates have suggested that NM-GHGs could play key roles in contributing to budgets of GHGs in the arid regions, whereas their global importance would be enhanced with accelerated global environmental changes. Therefore, more research should be undertaken, with a differentiation between NM-GHGs and M-GHGs, to further elucidate the underlying mechanisms, to investigate the impacts of various global change agents, and to quantify their contributions to regional and global GHGs budgets. These efforts will contribute to a more complete understanding of global carbon and nitrogen cycling and a reduction in the uncertainty of carbon-climate feedbacks in the Earth system.

Methane Feedbacks to the Global Climate System in a Warmer World

“…This includes mechanisms that are not driven by methanogenic archaea (e.g., Liu et al, 2015) or those that are governed by alternative pathways and nonoxygen sensitive enzymes (Tang et al, 2016), such as CH 4 production in freshwater lakes as a by-product of phosphorus metabolism rather than C or energy metabolism (Yao et al, 2016) or CH 4 production in oxygenated shallow marine waters by zooplankton (Schmale et al, 2017). There have been other recent indications of nonmicrobial CH 4 production, although only at very small levels insignificant in the context of the global CH 4 budget (Table 1) (Wang, Lerdau, & He, 2017). The presence of CH 4 in oxic zones in lakes is likely driven by the transport of dissolved CH 4 from CH 4 production areas, rather than aerobic, algae-related CH 4 production (Encinas Fernández et al, 2016).…”

Smith, K.A., Ball, T., Conen, F., Dobbie, K.E., Massheder, J. & Rey, A. 2003. Exchange of greenhouse gases between soil and atmosphere: interactions of soil physical factors and biological processes. European Journal of Soil Science, 54, 779–791.

“…Vigano et al, 2008;Fraser et al, 2015;Rey, 2015;Wang et al, 2017), which are more important in arid and semiarid environments. Vigano et al, 2008;Fraser et al, 2015;Rey, 2015;Wang et al, 2017), which are more important in arid and semiarid environments.…”

Thermal abiotic emission of CO2 and CH4 from leaf litter and its significance in a photodegradation assessment

“…, Wang et al. ), Lee et al. () found that thermal emission of CO 2 and CH 4 from dried green leaves of four species, as well as cellulosic filter paper and basswood wood, increased exponentially from 25°C to 55°C.…”

“…These emissions are typically very low at temperatures below 30°C, but increase exponentially at higher temperatures, particularly above %50°C (but well below the ignition point of organic matter). While this process is not well characterized (reviewed by Carmichael et al 2014, Wang et al 2017, Lee et al (2012) found that thermal emission of CO 2 and CH 4 from dried green leaves of four species, as well as cellulosic filter paper and basswood wood, increased exponentially from 25°C to 55°C. Rates varied appreciably among plant materials implying that chemical composition is a potential factor in emission rates.…”