Abstract
Bryophyte establishment represents a positive feedback process that enhances soil development in newly exposed terrain. Further, biological nitrogen (N) fixation by cyanobacteria in association with mosses can be an important supply of N to terrestrial ecosystems, however the role of these associations during post-glacial primary succession is not yet fully understood. Here, we analyzed chronosequences in front of two receding glaciers with contrasting climatic conditions (wetter vs drier) at Cordillera Darwin (Tierra del Fuego) and found that most mosses had the capacity to support an epiphytic flora of cyanobacteria and exhibited high rates of N2 fixation. Pioneer moss-cyanobacteria associations showed the highest N2 fixation rates (4.60 and 4.96 µg N g−1 bryo. d−1) very early after glacier retreat (4 and 7 years) which may help accelerate soil development under wetter conditions. In drier climate, N2 fixation on bryophyte-cyanobacteria associations was also high (0.94 and 1.42 µg N g−1 bryo. d−1) but peaked at intermediate-aged sites (26 and 66 years). N2 fixation capacity on bryophytes was primarily driven by epiphytic cyanobacteria abundance rather than community composition. Most liverworts showed low colonization and N2 fixation rates, and mosses did not exhibit consistent differences across life forms and habitat (saxicolous vs terricolous). We also found a clear relationship between cyanobacteria genera and the stages of ecological succession, but no relationship was found with host species identity. Glacier forelands in Tierra del Fuego show fast rates of soil transformation which imply large quantities of N inputs. Our results highlight the potential contribution of bryophyte-cyanobacteria associations to N accumulation during post-glacial primary succession and further describe the factors that drive N2-fixation rates in post-glacial areas with very low N deposition.
Highlights
Cryptogamic covers account for nearly half of the biological nitrogen (N) fixation on land [1], representing an important supply of N to terrestrial ecosystems
Our aims were (1) to describe how soil properties and N2 fixation related parameters change along two pro-glacial chronosequences at the Cordillera Darwin (Tierra del Fuego), (2) how species identity, climatic conditions, and the stage of ecological succession, influence N2 fixation rates of bryophytecyanobacteria associations, and thereby ecosystem N accumulation, and (3) whether any of these associations are species specific
We have shown that bryophyte-cyanobacteria associations have the potential to contribute to N accumulation very early after glacier retreat, a process that could help promote soil development
Summary
Cryptogamic covers account for nearly half of the biological nitrogen (N) fixation on land [1], representing an important supply of N to terrestrial ecosystems. Moss-associated cyanobacteria can provide 2–58% of the N input to Arctic ecosystems and in Antarctica the percentage can reach up to 84% [11]. The role of cyanobacteriamoss associations on N inputs has received considerably less attention, despite bryophytes being often the first plants to colonize newly exposed terrain [13]. The lack of studies is marked in temperate and subpolar regions of the Southern Hemisphere, where bryophytes account for more than 50% of the plant species [14]
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