Abstract

Dinitrogen (N-2) fixation associated with moss-dwelling bacteria (diazotrophs) is a N source in boreal forests. In feather moss-dominated understories of Fennoscandia, N-2 fixation rates increase with forest age due to N limitation. Whether this is applicable across different boreal ecosystems and successional pathways is not fully understood. In eastern Canada, increasing Sphagnum dominance starting about 100 years post-fire (paludification), is prevalent. Our main objectives were to determine how potential moss-associated N-2 fixation and relative contributions of Sphagnum and other mosses vary with time since fire and to explore the mechanisms driving observed patterns. Sampling was conducted in eight black spruce forests (Picea mariana; 64-724 years post-fire) in northwestern Quebec, Canada, along an established post-fire successional gradient. Potential N-2 fixation was measured with the acetylene reduction method in seven common moss species (Pleurozium schreberi, Hylocomium splendens, Dicranum polysetum, Sphagnum capillifolium, Sphagnum angustifolium, Sphagnum russowii, and Sphagnum magellanicum). N-2 fixation rates by moss communities were low and seemed to increase with stand age, but large variability was found between sites and species. The mechanisms underlying N-2 fixation rates were related to a switch in moss communities from feather moss to a Sphagnum dominance, which had the highest individual acetylene reduction rates, and to an increasing frequency of N-2-fixing samples in old forests. This study provided one of the first records of moss-associated N-2 fixation in eastern Canada and offers insights into how regional and cross-continental differences in moss community composition determine N cycling in boreal forests.

Keywords

Nitrogen fixation; Boreal forest; Feather moss; Sphagnum; Paludification

Published in

Plant Ecology
2021, volume: 222, number: 9, pages: 1007-1022
Publisher: SPRINGER

Authors' information