D. Hanelt et al., INFLUENCE OF UV-RADIATION ON THE PHOTOSYNTHESIS OF ARCTIC MACROALGAE IN THE FIELD, Journal of photochemistry and photobiology.B, Biology, 38(1), 1997, pp. 40-47
The photoinhibition in brown and red macroalgae from Spitsbergen (79 d
egrees N, 12 degrees E) was investigated to study the effects of UV un
der balanced UV/photosynthetically active radiation (PAR) conditions.
Algae were collected from different depths and exposed to natural sola
r radiation. Various parts of the UV radiation spectrum were successiv
ely cut off by filters absorbing wavelengths of less than 295 nm, less
than 320 nm and less than 400 nm. The samples were covered with these
filters and exposed to daylight 10 cm below the water surface in outd
oor tanks near the shore supplied with running seawater. PAR and UV ra
diation were continuously measured during the experiments. The degree
of photoinhibition was observed during the course of the day by measur
ing the in vivo fluorescence of photosystem II (F-v/F-m). In addition,
the transmittance of the water body of the Kongsfjord (Spitsbergen, N
orway) related to the UV and PAR wavelength ranges was determined. Eve
n on a sunny day in August, only relatively low fluence rates of UVA (
approximately 13 W m(-2)), UVB (approximately 0.14 W m(-2)) and PAR (a
pproximately 1100 mu mol m(-2) s(-1)) were measured in the air at noon
due to the low position of the sun at this high latitude. The UV tran
smittance of the water body in the fjord was also low. As a result, UV
stress occurred only in seaweeds growing in the intertidal zone or in
shallow water. The photoinhibition of photosynthesis was mainly induc
ed by white light in shallow water. The inhibitory effects of UV radia
tion caused a delay in the recovery processes in the afternoon and eve
ning, rather than an inhibitory effect on photosynthesis in the mornin
g. Fucus distichus, growing in the upper intertidal zone, was most ins
ensitive to UV radiation. Algae from the sublittoral zone had problems
coping with the natural UV radiation in shallow water, whereas those
from the intertidal zone were acclimatized to the unfavourable UV/PAR
conditions. By cutting off sequentially the shorter wavelengths of the
UV range, the investigated brown algae showed no significantly differ
ent effects. In contrast, the red alga Palmaria palmata showed a clear
response to the different UV ranges, i.e. the UVB wavelength range wa
s very effective in causing photoinhibition. In addition, the recovery
phase was delayed in spite of the low fluence rates impinging on the
alga during the course of the day. (C) 1997 Elsevier Science S.A.