Birch bark hosts hidden microbe communities shaped by sun and pollution
Brealey JC, Davey ML, Pedersen B
Urban Ecology
Next time you walk past a birch tree, run your hand over the bark on its north side versus south side, you're touching two genuinely different microscopic ecosystems shaped by sunlight and decades of air pollution history.
Tree bark isn't just dead wood covering, it's a living surface crawling with its own community of bacteria and tiny algae, distinct from what lives on leaves or in soil. Researchers studying Norwegian birch trees found that the north-facing side of a trunk often hosts more nitrogen-fixing cyanobacteria than the south-facing side, and that trees in areas with a history of heavy nitrogen pollution have swapped out those nitrogen-fixers for ordinary green algae instead. It's a reminder that every tree you pass is really a small, layered ecosystem responding to sun, wind, and decades of atmospheric chemistry.
Key Findings
Bacterial and algal communities on birch bark differed across three Norwegian sites but shared the same dominant taxa overall
At the most open, oceanic site, north-facing bark had a notably higher abundance of cyanobacteria than south-facing bark
Nitrogen-fixing cyanobacteria were more abundant at the site with the lowest historical nitrogen deposition, while non-diazotrophic green algae dominated at the highest-deposition site
chevron_right Technical Summary
Scientists found that birch tree bark hosts thriving communities of bacteria and algae, and which species live there depends on which side of the tree faces north versus south, and how much nitrogen pollution has historically fallen on the area.
Abstract Preview
Original paper
Bacterial and Green Algal Communities of Norwegian Birch Tree Bark.
Tree bark hosts a unique community of microorganisms, distinct from that of other plant tissues and from the microbial associates of macrophytic epiphytes. These corticolous communities are importa...
open_in_new Read full abstractAbstract copyright held by the original publisher.
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