Abstract
Background and aims
Nitrogen (N2) fixation in feather moss-cyanobacteria associations is a major source of N for boreal ecosystems. However, mosses experience significant shifts in their moisture status due to daily and yearly fluctuations in sunlight, temperature and precipitation. While the effects of drying and rewetting on nutrient leaching and photosynthesis in mosses have been studied, no attempt has been made to assess the consequences for N2 fixation in feather mosses.
Methods
We conducted an experiment in which we dried (3 day at 28 °C; <9 % of field moisture) and rewetted samples of the feather moss Pleurozium schreberi (Brid.) Mitt. that is colonized by N2-fixing-cyanobacteria to assess the influence on N2 fixation. Further, we tested how long it takes for N2 fixation to recover from a drying-rewetting cycle. In addition, we assessed how N2 fixation changes with incubation time with acetylene (2–65 h).
Results
A drying period of 3 days almost completely eliminated N2 fixation (<0.2 μmol m−2 h−1) in the moss. However, rates slowly recovered after rewetting, reaching N2 fixation levels of moist (non-water stressed) moss 5 days after rewetting. Nitrogen fixation increased significantly with incubation time with acetylene (0 μmol m−2 h−1 at 2 h vs. 26 μmol m−2 h−1 at 65 h incubation).
Conclusions
Although N2 fixation recommenced upon rewetting, the recovery was slow. Thus, recurrent drying and rewetting cycles could reduce total N2 fixation in moss-cyanobacteria associations over time, leading to reduced total N input to the system.
