The Sensitivity of Moss-Associated Nitrogen Fixation towards Repeated Nitrogen Input

• Published in: PloS one Vol. 11; no. 1; p. e0146655
• Main Authors: Rousk, Kathrin, Michelsen, Anders
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 05.01.2016; Public Library of Science (PLoS)
• Subjects: Betula pubescens; Boreal forests; Bryophyta; Bryophyta - physiology; Cyanobacteria; Cyanobacteria - physiology; Deprivation; Ecology; Ecosystem; Ecosystem biology; Ecosystems; Flowers & plants; Forests; Hylocomium splendens; Inhibition; Laboratories; Leachates; Mosses; Nitrates; Nitrogen; Nitrogen - metabolism; Nitrogen fixation; Nitrogen Fixation - physiology; Peatlands; Permafrost; Pleurozium schreberi; Sensitivity; Sphagnum; Taiga; Taiga & tundra; Tundra; Tundra ecology; United States
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0146655

Nitrogen (N2) fixation is a major source of available N in ecosystems that receive low amounts of atmospheric N deposition. In boreal forest and subarctic tundra, the feather moss Hylocomium splendens is colonized by N2 fixing cyanobacteria that could contribute fundamentally to increase the N pool in these ecosystems. However, N2 fixation in mosses is inhibited by N input. Although this has been shown previously, the ability of N2 fixation to grow less sensitive towards repeated, increased N inputs remains unknown. Here, we tested if N2 fixation in H. splendens can recover from increased N input depending on the N load (0, 5, 20, 80, 320 kg N ha(-1) yr(-1)) after a period of N deprivation, and if sensitivity towards increased N input can decrease after repeated N additions. Nitrogen fixation in the moss was inhibited by the highest N addition, but was promoted by adding 5 kg N ha(-1) yr(-1), and increased in all treatments during a short period of N deprivation. The sensitivity of N2 fixation towards repeated N additions seem to decrease in the 20 and 80 kg N additions, but increased in the highest N addition (320 kg N ha(-1) yr(-1)). Recovery of N in leachate samples increased with increasing N loads, suggesting low retention capabilities of mosses if N input is above 5 kg N ha(-1) yr(-1). Our results demonstrate that the sensitivity towards repeated N additions is likely to decrease if N input does not exceed a certain threshold.