Pleurozium schreberi and Nitrogen Fixation

I first became acquainted with this moss when I started to take workshops at Eagle Hill Institute in Maine. I would drive down the long gravel drive into Eagle Hill with woods on both sides. In places I would see what looked like monocultures of a mat moss. On closer look all the mosses had a very apparent reddish stem. All I could think was, what is this moss? It of course was Pleurozium schreberi.

And indeed, it did cover large swaths around Eagle Hill. It does occur in Ohio in numerous counties, but in much smaller patches than seen in Maine. In large sections of the Boreal Forest, it can account, along with another pleurocarpous moss, Hylocomium splendens (stair-step moss) up to 95% of the ground cover.

Why is this moss so common in these boreal areas? Researchers have found that this species commonly is associated with cyanobacteria that assist with N fixation. These mosses may be responsible for much of the N fixation that occurs in boreal areas.

It was found that Pleurozium schreberi alone fixes from 1.5 to 2.0 kg N ha-1 yr-1 in mid- to late-successional forests of northern Scandinavia and Finland. These are areas where otherwise there are very few other N fixing tree or forbs.

Large parts of the boreal area are dominated by infertile acid sandy soils—spodosols. It is in these kind of soil areas naturally low in N where N fixing plants thrive. They, along with possibly Hylocomium and associated cyanobacteria, may possibly be the most broadly distributed N fixers on earth.

It is uncertain though how much N fixation occurs in the Pleurozium that we find in Ohio, as fixation appears to mainly occur in low N deposition areas such as found in boreal forest areas—very much unlike Ohio.

Pleurozium schreberi Photo from Internet

One question is what happens to the N in these mosses and associated cyanobacteria? While it makes sense that N would “leak” from them, but whether this is transferred to the soil, and how much, and over how long a time period is unknown.

So the next time you see a patch of Pleurozium in Ohio or elsewhere, you can think of the large role it plays in the boreal ecosystem and how much there still is still to be learned about this intriguing moss.

Sources:

Feather mosses, nitrogen fixation, and the boreal biome. T. H. DeLuca School of the Environment and Natural Resources, Bangor University, Bangor, UK

DeLuca, T. H., Zackrisson, O., Nilsson, M.-C. and Sellstedt, A. (2002). Quantifying nitrogen-fixation in feather moss carpets of boreal forests. Nature 419, 917-920.

Rousk K, Jones DL, Deluca TH. Moss-cyanobacteria associations as biogenic sources of nitrogen in boreal forest ecosystems. Front. Microbiol. 2013;4:150. Published 2013 Jun 17. doi:10.3389/fmicb.2013.00150

-Bill Schumacher