New insight to the role of microbes in the methane exchange in trees: evidence from metagenomic sequencing.

Methane (CH ) exchange in tree stems and canopies and the processes involved are among the least understood components of the global CH cycle. Recent studies have focused on quantifying tree stems as sources of CH and understanding abiotic CH emissions in plant canopies, with the role of microbial in situ CH formation receiving less attention. Moreover, despite initial reports revealing CH consumption, studies have not adequately evaluated the potential of microbial CH 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 CH exchange of plants, and particularly in boreal trees. We detected CH -producing methanogens and novel monooxygenases, potentially involved in CH consumption, in coniferous plants. In addition, our field flux measurements from Norway spruce (Picea abies) canopies demonstrate both net CH emissions and uptake, giving further evidence that both production and consumption are relevant to the net CH exchange. Our findings, together with the emerging diversity of novel CH -producing microbial groups, strongly suggest microbial analyses should be integrated in the studies aiming to reveal the processes and drivers behind plant CH exchange.