Journal
NEW PHYTOLOGIST
Volume 214, Issue 1, Pages 97-107Publisher
WILEY
DOI: 10.1111/nph.14331
Keywords
biological nitrogen fixation; boreal forests cyanobacteria; Hylocomium splendens; molybdenum (Mo); phosphorus (P); Pleurozium schreberi; subarctic tundra
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Funding
- Danish Council for Independent Research and FP7 Marie Curie Actions - COFUND [DFF - 1325-00025]
- Danish National Research Foundation (Center for Permafrost, CENPERM) [DNRF100]
- Canadian Research Chair in Boreal Biogeochemistry [CRC-950-230570]
- Natural Sciences and Engineering Research Council of Canada through a Strategic grant [305985129]
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Biological nitrogen fixation (BNF) performed by moss-associated cyanobacteria is one of the main sources of new nitrogen (N) input in pristine, high-latitude ecosystems. Yet, the nutrients that limit BNF remain elusive. Here, we tested whether this important ecosystem function is limited by the availability of molybdenum (Mo), phosphorus (P), or both. BNF in dominant mosses was measured with the acetylene reduction assay (ARA) at different time intervals following Mo and P additions, in both laboratory microcosms with mosses from a boreal spruce forest and field plots in subarctic tundra. We further used a N-15(2) tracer technique to assess the ARA to N-2 fixation conversion ratios at our subarctic site. BNF was up to four-fold higher shortly after the addition of Mo, in both the laboratory and field experiments. A similar positive response to Mo was found in moss colonizing cyanobacterial biomass. As the growing season progressed, nitrogenase activity became progressively more P limited. The ARA : N-15(2) ratios increased with increasing Mo additions. These findings show that N-2 fixation activity as well as cyanobacterial biomass in dominant feather mosses from boreal forests and subarctic tundra are limited Mo availability.
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