Abstract
Methane (CH4 ) exchange in tree stems and canopies and the processes involved are among the least understood components of the global CH4 cycle. Recent studies have focused on quantifying tree stems as sources of CH4 and understanding abiotic CH4 emissions in plant canopies, with the role of microbial in situ CH4 formation receiving less attention. Moreover, despite initial reports revealing CH4 consumption, studies have not adequately evaluated the potential of microbial CH4 oxidation within trees. In this paper, we discuss the current level of understanding on these processes. Further, we demonstrate the potential of novel metagenomic tools in revealing the involvement of microbes in the CH4 exchange of plants, and particularly in boreal trees. We detected CH4 -producing methanogens and novel monooxygenases, potentially involved in CH4 consumption, in coniferous plants. In addition, our field flux measurements from Norway spruce (Picea abies) canopies demonstrate both net CH4 emissions and uptake, giving further evidence that both production and consumption are relevant to the net CH4 exchange. Our findings, together with the emerging diversity of novel CH4 -producing microbial groups, strongly suggest microbial analyses should be integrated in the studies aiming to reveal the processes and drivers behind plant CH4 exchange.
Highlights
The first evidence on aerobic methane (CH4) emissions by terrestrial vegetation was provided by Keppler et al (2006), estimating that plants – including woody and grass species – are a large source of CH4
Discussion on aerobic plant CH4 production has mainly concentrated on plant physiology, which was recently reviewed by L
Potential microbial CH4 production within the aboveground tree habitat remains less studied in comparison with other mechanisms
Summary
Methane (CH4) exchange in tree stems and canopies and the processes involved are among the least understood components of the global CH4 cycle. Recent studies have focused on quantifying tree stems as sources of CH4 and understanding abiotic CH4 emissions in plant canopies, with the role of microbial in situ CH4 formation receiving less attention. Despite initial reports revealing CH4 consumption, studies have not adequately evaluated the potential of microbial CH4 oxidation within trees. We demonstrate the potential of novel metagenomic tools in revealing the involvement of microbes in the CH4 exchange of plants, and in boreal trees. We detected CH4-producing methanogens and novel monooxygenases, potentially involved in CH4 consumption, in coniferous plants. Together with the emerging diversity of novel CH4-producing microbial groups, strongly suggest microbial analyses should be integrated in the studies aiming to reveal the processes and drivers behind plant CH4 exchange
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