Rates of carbon flux in 14 species of Antarctic bryophytes were
measured
under controlled conditions using an
infra-red gas analysis system. The results were used to produce estimates
of
model parameters for respiration and
photosynthesis. The relationships between respiration, photosynthesis,
irradiance
and temperature followed
standard patterns. Temperature optima for gross and net photosynthesis
were
10–20 and 0–20°C respectively,
suggesting that the plants were not truly psychrophilic. Photosynthesis
was
saturated at 30–270 μmol m−2 s−1,
consistent with the view that bryophytes are, physiologically, shade plants,
although there was no evidence of
photoinhibition over the range of irradiances tested (up to 700
μmol m−2 s−1). Comparison of the results
with
environmental data suggests that photosynthesis is usually temperature-limited
during daylight in the growing
season. Therefore, any change in the temperature of the habitat could
affect the productivity of the bryophytes.
Rates of photosynthesis varied widely between species, and these
relationships were largely maintained over the
range of temperatures and irradiances tested. Photosynthetic rankings were
correlated with the water availability
in the plant habitats, supporting the hypothesis that water is the important
factor in determining the distribution
of populations in Antarctic habitats.