Slow growth and decomposition of mosses in Arctic lakes

Abstract

Aquatic mosses are often the exclusive form of macrophytic vegetation in Arctic lakes. Despite the cold nutrient-poor water and the short ice-free summer, the mosses form dense stands on the lake bottom down to great depths. The environmental conditions suggest that moss growth and decomposition are extremely slow, but logistical and methodological difficulties have so far precluded direct measurements of the processes. Here, we use temporal changes in the size and density of leaves along the axis of moss shoots collected from different depths in Char Lake and North Lake in the Canadian High Arctic to reconstruct the annual growth and decomposition of the mosses during the past 10-17 years. Our results show low but remarkably constant annual elongation rates (about 10 mm·shoot -1 ) in the long-lived shoots that carry green leaves for several years and decompose slowly. Cold temperatures and low nutrient supply in combination with the short Arctic growing season can account for the low growth rate, the low decomposition rates, and the unprecedented longevity of these moss communities relative to other submerged macrophytes.

Mosses in High-Arctic lakes: in situ measurements of annual primary production and decomposition

“…The moss decomposition rate estimated from litter bag experiments on S. scorpioides was around 0.15 year -1 in Lake Sommerfuglesø. This decomposition rate is in close agreement with the decomposition rates determined for aquatic mosses in High-Arctic Canadian lakes (0.11-0.18 year -1 ) when calculated from biomass decrease in older growth segments (Sand-Jensen et al 1999). There was no difference in decomposition rates between the two mesh sizes in the decomposition study, indicating that no invertebrates larger than 200 lm used the moss directly as a food resource.…”

“…Drepanocladus revolvens var. intermedius and Calliergon giganteum in Char Lake (1.0-2.8 mg shoot -1 year -1 ; Sand- Jensen et al 1999) determined by reconstruction methods. However, it was low compared to another direct growth measurements by Priddle (1980) made for moss carpet habitats in an Antarctic lake (40 gC m -2 year -1 ).…”

“…Thus, only few direct quantitative measurements of moss primary production have been reported (Priddle 1980;Finlay and Bowden 1994), and these were reports on short-term measurements of primary production rates during summer without any attempt to scale up to annual production. Annual primary production of Arctic lake moss vegetation has been estimated using annual growth segments (Sand-Jensen et al 1999;Hawes et al 2002), also but this method relies on morphological distinct annual growth segments developing in certain moss species (Riis and Sand-Jensen 1997;Riis et al 2014).…”

Rare Moss-Built Microterraces in a High-Altitude, Acid Mine Drainage-Polluted Stream (Cordillera Negra, Peru)

“…This is well in accordance with growth rates observed in similar extreme environments, such as for Bryum pseudotriquetrum in continental Antarctica (Selkirk and Skotnicki 2007) and for mosses in Arctic lakes and streams (e.g. Sand-Jensen et al 1999). Moreover, accumulation rates in Bryophyte dominated mires and peats in the high-altitude Peruvian Puna peatlands were found to be in the order of 2 mm/year (Salvador et al 2014/15).…”

The Role of Bryophytes in Carbon and Nitrogen Cycling

“…Riis & Sand-Jenson 1997;Sand-Jenson et al 1999), and bryophyte NPP can exceed that of epilithic or periphytic algae (Stream Bryophyte Group 1999). Aquatic bryophyte production can be comparable to growth in terrestrial systems, but varies widely with microhabitat and among species.…”