Nitrogenase Activity in Relation to Intracellular Organisms in Sphagnum Mosses

Abstract

Electron microscopic studies oiSphagnum lindbergii (Schimp.) and S. riparium (Angstr.) bave revealed tbe presence of intracellular organisms sucb as blue-green algae, green algae, bacteria and fungi.Nitrogenase activities of tbese Sphagnum mosses were found to be related mainly to tbe presence of intracellular Nostoc filaments. Tbe appearance of nitrogen-fixing blue-green algae witbin bryopbytes is tbus not restricted to liverworts. The association is likely to be of ecological importance as it .seems to occur in very acid babitats generally lacking blue-green algae.Possible interrelations between tbe moss, tbe blue-green algae and different types of bacteria are discussed.

Field studies of nitrogen fixation of Australian alpine plants and soils

“…A more probable explanation of the activity of the blue-green algae living in these very acid environments is that they themselves are capable of limited adaptive self-buffering possibly via their own slime sheaths, and that the close association with the Sphagnum cells enables them to take advantage of the increased cation concentration at the Sphagnum leaf surface -a form of epontic existence in what is otherwise a cation-poor environment. This accords with Granhall & Hofsten's (1976) observation that such close associations are not found in minerotrophic parts of sub-arctic tundra in Sweden.…”

“…Tests on Sphagnum from the Brindabellas showed that white light at 335 J m"^ sec"' did not penetrate as far as 15 cm. No data are given by the authors (or by Granhall & Hofsten 1976) to show whether any acetylene reduction could go on in the dark. The incubations were for 2 hr at 9-14°C, always in daylight (except for peat samples) and the samples were small, since 7 ml serum bottles were used as containers.…”

“…The algae were usually epiphytic on the leaves of the moss but in one, 5. lindbergii, Nostoc filaments were included in 5-10% of the hyaUne cells of the upper leaves of the plants. Granhall & Hofsten (1976) have enlarged on this latter observation and claim a specific nitrogen-fixing association of Nostoc with hyaline cells of two species of Spagnum. No filamentous or other blue-green algae were evident in the Sphagnum of the moss beds of the Bogong High Plains.…”

“…Stewart (1974) states that fixation by bluegreen algae is unlikely to proceed at such low pH values as 4.5. Granhall & Hofsten (1976)seekto explain what they believe to be the unusual effectiveness of blue-green algal filaments intracellular in Sphagnum as attributable to a favourable environment within the hyaline cells 'due to their buffering capacity'. But the water in the empty hyahne cells with their very large pores is necessarily part of the bulk phase water and theoretically at least ought to share the same pH value.…”

Nitrogen cycling in a forested Minnesota bog

“…For instance, numerous studies on N fixation in peat have shown highly variable results reflecting the different agents of fixation that may predominate and the different strata of peat sampled (Waughman andBellamy 1972, 1980;Dooley and Houghton 1973;Granhall and Selander 1973;Granhall and Lid-Torsvik 1975;Blasco and Jordan 1976;Alexander et al 1978; Barsdate and Alexander 1975;Dierberg and Brezonik 1981;Chapman and Hemond 1982). Most studies on N fixation and denitrification in peat (e.g., Granhall 1970;Waughman andBellamy 1972, 1980;Kallio and Kallio 1975;Granhall and Hofsten 1976;Waughman 1976;Basilier et al 1978;Muller et al 1980) have consisted of short-term measurements in the laboratory with small quantities of moss or subsurface peat. In few cases (e.g., Martin and Holding 1978;Hemond 1983) were kinetic parameters measured to allow extrapolation to field conditions.…”