Bryophyte-cyanobacterial associations as a key factor in N2-fixation across the Canadian Arctic

Abstract

Nitrogen inputs via biological N2-fixation are important in arctic environments where N often limits plant productivity. An understanding of the direct and indirect theoretical causal relationships between key intercorrelated variables that drive the process of N2-fixation is essential to understanding N input. An exploratory multi-group Structural Equation Modeling (SEM) approach was used to examine the direct and indirect effects of soil moisture, plant community functional composition, and bryophyte and lichen abundance on rates of nitrogen fixation at a low arctic ecosystem, two high arctic oases and a high arctic polar desert in the Canadian Arctic. Increasing soil moisture was strongly associated with an increas- ing presence of bryophytes and increasing bryophyte abundance was a major factor determining higher N2- fixation rates at all sites. Shrubs had a negative effect on bryophyte abundance at all sites with the exception of the polar desert site at Alexandra Fjord highland. The importance of competition from vascular plants appears to be greater in more productive sites and may increase at lower latitudes. Moisture availability may have an indirect effect on ecosystem develop- ment by affecting N input into the system with bryophyte-cyanobacterial associations playing an im- portant intermediary role in the process.