Trees are not passive chimneys venting greenhouse gases from the soil, but function as active biochemical reactors. This is the finding of research conducted in wet forests of north-eastern New South Wales, Australia, where microbial communities in tree bark simultaneously produce and consume multiple climate-active gases. The study, published on 8 January in Science, focuses primarily on the broad-leaved paperbark Melaleuca quinquenervia.
Measurements on tree trunks show that these trees can be net emitters of carbon dioxide and methane, whilst simultaneously taking up hydrogen and carbon monoxide – gases that indirectly influence atmospheric chemistry. The researchers measured gas fluxes directly on the trunk using sealed measurement chambers, and in doing so also mapped oxygen gradients within the bark (see photo). These gas fluxes vary considerably with season, trunk height, and oxygen availability in the bark. In the lower sections of the trunk in particular, oxygen-depleted micro-environments arise readily, in which methane production can predominate. Higher up the trunk, where more oxygen penetrates, micro-organisms that consume methane and hydrogen dominate instead.
According to the authors, this calls for an adjustment of climate models, which have largely ignored tree trunks until now, although it remains unclear exactly how large this contribution is on a global scale.