The Assessment of Nitrogen Fixation and Throughput by Lichens

Abstract

SUMMARYThalli oi Peltigera membranacea, Peltigera polydactyla and Lobaria pulmonaria were labelled witĥ *N and subjected to simulated episodes of heavy rainfall after periods of drying in a lighted air-conditioned incubator. Inorganic and total nitrogen was estimated in the eluates. The drying-wetting cycle was repeated three times. From the level of ^^N labelling of the eluates, it was evident that recently fixed nitrogen was released, the inorganic fraction (NH4"^) being up to three times more heavily labelled than the organic. The amounts of nitrogen lost in successive episodes generally diminished in logarithmic fashion, the level of labelling remaining approximately constant, implying little or no replenishment of mobile material from insoluble reserves. Up to three times the total nitrogen fixed per day could be lost in one rainfall episode. A preliminary trial showed that nitrogen losses from thalli under less rigorous regimes could be of nutritional benefit to the underlying moss substratum.

Patterns and Controls on Nitrogen Cycling of Biological Soil Crusts

“…Kershaw (1985) reported that 19-28 % of labeled N applied to lichens was later found in surrounding soils. Earlier studies showed more N release when pH, temperature, light, CO 2 , or ionic conditions were suboptimal or during wetting after desiccation (Henriksson 1957;Jones and Stewart 1969a;Millbank 1982;Jeanfils and Rack 1992). Nitrogen release may occur very quickly once biocrust organisms become physiologically active.…”

“…Extracellular release of nitrogenous compounds, including inorganic forms such as nitrate [NO 3 À ] and ammonium [NH 4 + ], and small amounts of amide, peptides, and free amino acids, occurs in both cyanobacteria and lichens (Stewart 1970;Millbank 1982). Nitrogen release is especially pronounced in the presence of N-fixing organisms, which can release 5-70 % of N fixed (Magee and Burris 1954;Silvester et al 1996).…”

Factors Influencing Nitrogen Fixation and Nitrogen Release in Biological Soil Crusts

“…Extracellular release of nitrogenous compounds occurs in both cyanobacteria and lichens (Stewart 1970;Millbank 1982). It is especially pronounced in N-fixing organisms, which release 5-70 % of N fixed.…”

Vertical distribution, nitrogen content, and natural 15n and 13c abundance of epiphytic macrolichen functional groups and soil in sub-boreal spruce forests of central British Columbia.

“…Nutrients held in lichens positioned within the canopy are released into the forest system by intermittent leaching (Millbank, 1982). Lichens do not provide energy, nutrients or water directly to the vascular system of their host tree directly.…”

“…Nitrogen that is held in epiphytic lichens, and most importantly cyanolichens, can be released into the forest system and provide forest canopies and understory plants with N through intermittent leaching (Millbank 1982;Benzing 1990) and decomposition of lichen litterfall biomass (Campbell et al, 2010b). Research has established that nutrient leaching depends on lichen structure, amount of precipitation and surface area to volume ratio, but its quantification has not been properly assessed in sub-boreal forests of central BC.…”