Host Identity as a Driver of Moss-Associated N2Fixation Rates in Alaska

Moss-associated N(2)fixation provides a substantial but heterogeneous input of new N to nutrient-limited ecosystems at high latitudes. In spite of the broad diversity of mosses found in boreal and Arctic ecosystems, the extent to which host moss identity drives variation in N(2)fixation rates remains largely undetermined. We used(15)N(2)incubations to quantify the fixation rates associated with 34 moss species from 24 sites ranging from 60 degrees to 68 degrees N in Alaska, USA. Remarkably, all sampled moss genera fixed N-2, including well-studied feather and peat mosses and genera such asTomentypnum, Dicranum, andPolytrichum. The total moss-associated N(2)fixation rates ranged from almost zero to 3.2 mg N m(-2)d(-1), with an average of 0.8 mg N m(-2)d(-1), based on abundance-weighted averages of all mosses summed for each site. Random forest models indicated that moss taxonomic family was a better predictor of rate variation across Alaska than any of the measured environmental factors, including site, pH, tree density, and mean annual precipitation and temperature. Consistent with this finding, mixed models showed that trends in N(2)fixation rates among moss genera were consistent across biomes. We also found hotspots of high fixation rates in one-fourth of sampled sites. Our results demonstrated the importance of moss identity in influencing N(2)fixation rates. This in turn indicates the potential utility of moss identity when making ecosystem N input predictions and exploring other sources of process rate variation.

Automated summary

Moss-associated N(2)fixation provides varying input of new nitrogen to high-latitude ecosystems. Moss taxonomic family is a better predictor of fixation rate variation in Alaska than environmental factors. High fixation rate hotspots were found in a quarter of sampled sites.