Nutrient exchange in an Antarctic macrolichen during summer snowfall–snow melt events

Abstract

 Concentrations of NH% + , NO $ − , PO % $−, K + , Ca# + and Mg# + in snow meltwater resulting from summer snow showers were monitored before and after its passage through monospecific stands of the Antarctic macrolichen Usnea sphacelata R. Br. The sampling was conducted under field conditions near Casey Station in East Antarctica between January and March. Total snow deposition during the 61-d period was 44p1 mm (rainfall equivalent depth) delivering 362p10, 87p2 and 9p1 µmol m −# of NH % + , NO $ − and PO % $−, respectively. Meltwater that had percolated through U. sphacelata was depleted in NH % + and NO $ − equating with a retention by the lichen of 87 and 92 %, respectively, of the total wet deposition of these ions. Lichen-modified meltwater was slightly enriched in PO % $−, but because the volume of the lichen percolate was smaller than that of the original snow deposition, the lichen achieved a net gain of 9 % of the total P deposited. Lichen percolate was also enriched in metal cations. Potassium loss associated with the melting of the heaviest snowfall (18 mm) was equivalent to only 0n05 % of the total K in the lichen suggesting that ion loss did not signal significant cellular damage. There was also a progressive increase in NH % + concentration in unmodified meltwater from 3 to 21 nmol ml −" over a 3-d period whereas levels in the lichen-modified meltwater remained unchanged at 4 nmol ml −" . This enrichment in NH % + might have resulted from dry deposition onto the melting snow pack of NH $ emitted from nearby penguin rookeries. During the study, tagged thalli of U. sphacelata made a 2 % loss in dry mass although they appeared healthy and, at the end of the study, showed an effective quantum yield (∆F\Fmh) comparable with field material. The results are discussed in relation to the time of year that is likely to be most suitable for lichen growth in this continental Antarctic environment and the potential growth-led demand for N in U. sphacelata.

External nutrient inputs into terrestrial ecosystems of the Falkland Islands and the Maritime Antarctic region

“…However, at Signy Island, most lichens had a significantly lower signature than that of the wind blown material, indicating that they are unlikely to rely on this source of nitrogen. Their signature was more similar to that of precipitation, from which many lichens are known to obtain nutrients (Greenfield 1992b;Crittenden 1998;Hyvarinen and Crittenden 1998), rather than soil (Ellis et al 2004).…”

“…However, only a few studies have investigated the utilisation of these external sources by vegetation in Antarctic terrestrial ecosystems (Greenfield 1992b;Erskine et al 1998). Large but spatially localised and mostly coastal bird and seal colonies are known to influence vegetation in their vicinity through extra nitrogen deposition (Lindeboom 1984;Staley and Herwig 1993;Crittenden 1998). Penguin colonies, in particular, are associated with large guano deposits.…”

“…Large differences in stable isotope composition are already known to exist between mosses and lichens from the Antarctic (Galimov 2000;Huiskes et al 2006). These differences partly result from the utilisation of different nitrogen sources by these cryptogams (Crittenden 1998;Wainright et al 1998). Analyses of the different potential sources of nitrogen for their 15 N content should, therefore, provide clarification of the origin of external nitrogen into these ecosystems.…”

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.…”

Influence of the ice growth rate on the incorporation of gaseous HCl

“…The understanding of snow composition is crucial for numerous scientific fields such as ice core inversions (Domine et al, 1995;Legrand and Mayewski, 1997), air-snow interactions (Domine and Shepson, 2002), hydrology (Tranter et al, 1986;Cragin et al, 1993;Domine and Thibert, 1995) and ecology (Crittenden, 1998). Snow on the ground undergoes metamorphism, a set of physical processes which includes sublimation-condensation cycles that lead to changes in the size and shapes of snow crystals (Colbeck, 1982;Domine et al, 2003).…”