Antarctic Science

Papers—Life Sciences and Oceanography

Ecophysiological investigations of Usnea antarctica in the maritime Antarctic I. Annual microclimatic conditions and potential primary production

Burkhard Schroeter a1c1, M. Olech a2, L. Kappen a1a3 and W. Heitland a4
a1 Botanisches Institut, Universität Kiel, Olshausenstraße 40, D-24098 Kiel, Germany
a2 Institute of Botany, Jagellonian University, 31-512 Kraków, Lubicz 46, Poland
a3 Institut für Polarökologie, Universität Kiel, Wischhofstr. 1-3, Geb. 12, D-24148 Kiel, Germany
a4 Lehrstuhl für Angewandte Zoologie, Universität München, Hohenbachernstr. 22, D-85354 Freising, Germany

Article author query
schroeter b   [PubMed][Google Scholar] 
olech m   [PubMed][Google Scholar] 
kappen l   [PubMed][Google Scholar] 
heitland w   [PubMed][Google Scholar] 


Photosynthetic photon flux density (PPFD), air relative humidity and thallus temperature (TT) were measured in Usnea antarctica over a period of 12 months at a coastal rock on King George Island, South Shetland Islands. TT had an annual amplitude of c. 54 K with the maximum of +27.4°C recorded in December and minimum of −27.3°C in July. Daily maximum TT exceeded 0°C every month except in June and July when they were below −0.4°C and −1.6°C, respectively. Daily minimum temperatures were always below zero. Diel courses of PPFD showed pronounced seasonal differences between summer (more than 2000 μmol m−2s−1) and winter (less than 50 μmol m−2s−1 in July). Daily sum of PPFD was highest (more than 30 mol m−2d−1) in December and lowest (0.1 mol m−2d−1) in July. A photosynthesis model was used to estimate the potential annual primary production from habitat PPFD and TT. The estimated potential annual carbon balance of U. antarctica was 323 mg CO2 g−1 dry weight y−1 assuming that the lichen was always at optimal moisture. The potential carbon balance indicates that primary production is severely limited by low PPFD and subzero TT in the austral winter. Nevertheless, the PPFD and TT would allow metabolic activity during winter but with a negative carbon balance during May–August. Spring and autumnal months are revealed as probably the most important periods for lichen primary production because PPFD exceeds photosynthetic light compensation point during the daytime and ambient moisture conditions frequently favour a positive carbon balance.

(Received August 22 1994)
(Accepted May 6 1995)

Key Words: lichen; maritime Antarctic; microclimate; photosynthesis; primary production; Usnea.

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