Nitrogen retention by Sphagnum mosses: responses to atmospheric nitrogen deposition and drought

Abstract

Sphagnum mosses are assumed to be effective at acquiring low amounts of nitrogen (N) in precipitation to support annual growth. However, N concentrations in precipitation have increased from anthropogenic sources over the last 150 years. I hypothesized that N retention from wet atmospheric deposition decreases with increased N availability, by comparing Sphagnum mosses in a high N deposition region in the Adirondack Park, New York, to a low-deposition region in eastern Maine. A 15 NH 4 15 NO 3 tracer was applied to mosses in both regions, and retention after 24 h was estimated. Nitrogen retention ranged from 50 to 90% of N applied. Most 15 N was recovered from the apical capitula and upper stems. Nitrogen retention was greater in the Maine sites in 1998. However, in 1999, a drought year, particularly in Maine, N retention was less in Maine than in New York. The drier climate appeared to lower N retention, possibly through its physiological effects on the mosses. Although atmospheric deposition might be the only exogenous source of N, it satisfied only a small fraction of N required for annual growth. These data suggest that internal cycling processes, such as mineralization, may be much more important N sources to support Sphagnum growth.Résumé : On assume que les mousses du genre Sphagnum (sphaignes) sont efficaces à acquérir de faibles quantités d'azote (N) à partir des précipitations, pour supporter leur croissance annuelle. Cependant, les teneurs en N de sources anthropogènes dans les précipitations ont augmenté au cours des 150 dernières années. Ayant comparé des sphaignes du parc des Adirondack (New York), une région à forte déposition de N, avec celles d'une région à faible déposition dans l'est du Maine, l'auteur formule l'hypothèse que la rétention de l'azote à partir de précipitations atmosphériques humides diminue avec une augmentation de la disponibilité de N. L'auteur a appliqué le traceur 15 NH 4 15 NO 3 sur des mousses des deux régions, et en a estimé la rétention après 24 h. La rétention de l'azote va de 50 à 90 % de l'azote appliqué. La majeure partie du 15 N se situe dans les capitules apicaux et la partie supérieure des tiges. La rétention a été plus forte sur les sites du Maine en 1998. Cependant, en 1999, une année sèche, surtout dans le Maine, la rétention de N à été plus faible dans le Maine que dans l'état de New York. Le climat plus sec semble diminuer la rétention, possiblement via ses effets physiologiques sur les mousses. Bien que la déposition atmosphérique puisse être la seule source exogène de N, elle ne remplit qu'une petite partie des besoins en N pour la croissance annuelle. Ces données suggèrent que les processus de cyclage interne, tels que la minéralisation, pourraient être des sources de N beaucoup plus importantes pour supporter la croissance des sphaignes.

Nitrogen Transfer from Four Nitrogen-Fixer Associations to Plants and Soils

“…Similarly, given the close proximity of root nodules and surrounding soil, legumes likely lose more N to the soil than rootless lichens and mosses, whose connections to soil are limited and which decompose slowly (Hobbie 1996;Cornelissen and others 2007). In addition, mosses and lichens are extremely efficient in retaining and recycling acquired N (Oechel and Van Cleve 1986;Crittenden 1998;Aldous 2002;Rousk and others 2014) and therefore regulate the amount and timing of N input to the system (see also Lindo and others 2013). These collective observations suggest that the range of N 2 fixers in the subarctic differ fundamentally in timing and amount of N release to the ecosystems.…”

The limiting roles of nitrogen and moisture on Sphagnum angustifolium growth over a depth to water table gradient

“…In accordance with the triphasic model (Lamers et al 2000), Sphagnum, in areas characterized by lower nitrogen regimes, has had higher nitrogen retention (Li and Vitt 1997), and increased growth with higher nitrogen inputs (Vitt et al 2003), yet the effects of incoming nitrogen retention also can be confounded by climatic factors such as drought (Aldous 2002a). In spite of this efficient uptake of nitrogen, there are striking deficits of incoming atmospheric nitrogen required to meet the growth demands of Sphagnum primary production in peatlands (Hemond 1983;Damman 1988;Urban and Eisenreich 1988;Aldous 2002b).…”

“…In addition to being dominant peat-forming plants, Sphagnum mosses are also recognized for their ability to efficiently up-take and retain aerially deposited nitrogen (Woodin and Lee 1987;Li and Vitt 1997;Aldous 2002a). In accordance with the triphasic model (Lamers et al 2000), Sphagnum, in areas characterized by lower nitrogen regimes, has had higher nitrogen retention (Li and Vitt 1997), and increased growth with higher nitrogen inputs (Vitt et al 2003), yet the effects of incoming nitrogen retention also can be confounded by climatic factors such as drought (Aldous 2002a).…”

How bird droppings can affect the vegetation composition of ombrotrophic bogs

“…Since most Irish bogs suffer from the effects of water table draw-down as a result of small-scale peat extraction and the presence of drainage ditches, reduced water input from precipitation may enhance the water shortage for ombrotrophic vegetation. In Sphagnum suffering from water stress, gas exchange is suppressed, resulting in reduced photosynthetic rates and growth (Hayward and Clymo 1983;Schipperges and Rydin 1998), reduced immobilization of nutrients by the Sphagnum layer (Aldous 2002), and increased availability of nutrients for vascular plants. All these processes will ultimately stimulate the growth of atypical grasses and trees and are disastrous for characteristic ombrotrophic species.…”