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Biology researchers discover that bacteria living in mosses on tree branches twice as effective at 鈥榝ixing鈥� nitrogen as those on the ground

A new study by Dr. Zo毛 Lindo, a post-doctoral fellow in the Department of Biology at 捆绑SM社区, and Jonathan Whiteley, a doctoral student in the same department, shows that large, ancient trees may be very important in helping forests grow.

These findings highlight the importance of maintaining the large old-growth trees in the coastal temperate rainforests that stretch from Southern Alaska to Northern California. Lindo鈥檚 findings suggest that it is the interactions between old trees, mosses and cyanobacteria, which contribute to nutrient dynamics in a way that may actually sustain the long-term productivity of these forests.

鈥淲hat we鈥檙e doing is putting large old trees into a context where they鈥檙e an integral part of what a forest is,鈥� says Dr. Lindo. 鈥淭hese large old trees are doing something: 听they鈥檙e providing habitat for something that provides habitat for something else that鈥檚 fertilizing the forest. 听It鈥檚 like a domino effect; it鈥檚 indirect but without the first step, without the trees, none of it could happen.鈥�

There are three players in this story: 1) large, old trees; 2) mosses that grow along their branches; and 3) a group of bacteria called cyanobacteria associated with the mosses. The cyanobacteria take nitrogen from the atmosphere and make it available to plants鈥揳 process called 鈥渘itrogen fixation鈥� that very few organisms can do.

The growth and development of many forests is thought to be limited by the availability of nitrogen. Cyanobacteria in mosses on the ground were recently shown to supply nitrogen to the Boreal forest, but until now cyanobacteria have not been studied in coastal forests or in canopies (tree-tops). By collecting mosses on the forest floor and then at 15 and 30 metres up into the forest canopy, Lindo was able to show both that the cyanobacteria are more abundant in mosses high above the ground, and that they 鈥渇ix鈥� twice as much nitrogen as those associated with mosses on the forest floor.

Moss is the crucial element. The amount of nitrogen coming from the canopy depends on trees having mosses.

鈥淵ou need trees that are large enough and old enough to start accumulating mosses before you can have the cyanobacteria that are associated with the mosses,鈥� Lindo said. 鈥淢any trees don鈥檛 start to accumulate mosses until they鈥檙e more than 100 years old. So it鈥檚 really the density of very large old trees that are draped in moss that is important at a forest stand level. We surveyed trees that are estimated as being between 500 and 800 years old.鈥�

The research was funded by the Natural Sciences and Engineering Research Council of Canada (NSERC).

For an abstract of the article:

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