Competition for newly fixed N2 within the boreal bryosphere. moss metagenome

The boreal forest is the largest terrestrial ecosystem in the world and its productivity is primarily regulated by nitrogen (N) availability. Biological N fixation by feather mosses-cyanobacteria associations may be the single largest N input to boreal ecosystems; however, our knowledge of N dynamics within the bryosphere remain inadequate. For the first time and under natural conditions we show that N2 fixed by cyanobacteria in feather mosses is found in multiple recipients within the complex moss-microbiota system before entering the larger ecosystem. The fixed N can be incorporated into photosynthetically active moss tissue or taken up by resident bacteria, fungi and micro-algae. The pathway for N uptake has implications for how rapidly N is turned over. N taken up by moss tissue is likely cycled slowly when compared to N captured by bacteria and fungi within the bryosphere. These results highlight the role of bryosphere microorganisms in mediating the gateway to the boreal N cycle and emphasize the need for a better ecological understanding of the microbial dynamics of the bryosphere.