Biology Reference
In-Depth Information
Fig. 1.2
Photosynthetic efficiency of the red alga
Palmaria palmata
during the course of the day.
The day was cloudy and the fluence rate decreased continuously after 14:10 h. The photosynthetic
efficiencies of the nonphotoinhibited controls, collected the day before from a depth of 1 m, were
measured by the fluorescence ratio
F
v
/
F
m
and standardized to 100%. The
solid fitted line
indicates
the inhibition caused by unfiltered sun radiation. The
broken
and the
dotted lines
represent the
inhibition caused by radiation depleted of different UV wavelength ranges. Next morning (8:30),
photosynthesis was measured again (after Hanelt et al.
1997a
)
protection against photodamage (Sicora et al.
2003
). Generally, field experiments
at latitudes with a low UV environment (e.g., polar region) do never show UV-B
repair effects in macroalgae (Hanelt et al.
1997a
,
b
,
c
; Bischof et al.
2000b
).
This indicates a special adaptation of organisms to UV-B when they live in an
environment with high solar radiation under high UV pressure. However, algae
growing in deeper, UV-protected locations on the shore are more sensitive to the
natural UVR as for instance the red alga
Palmaria palmata
(Hanelt et al.
1997a
).
This species shows a reaction which is clearly dependent on the different UVR
ranges. By cutting off successively the shorter wavelengths ranges, the degree of
photoinhibition decreases and recovery commences earlier during the course of the
day (Fig.
1.2
).
Various factors contribute to the individual sensitivity of algae toward solar
radiation, e.g., growth depth (Sagert et al.
1997
; Dring et al.
1996
; Bischof et al.
1998b
), season (G´mez et al.
1995a
), position within and below the canopy
(Stengel and Dring
1998
), life history stage as well as the different parts and
sizes of the thalli (G´mez et al.
1995b
; Dring et al.
1996
; Hanelt et al.
1997b
;
Karsten and Wiencke
1999
). Thus, acclimation to the ambient radiation plays an
important role in photosynthesis of marine macroalgae. A study on three abundant
brown algal species from Spitsbergen (
Saccharina latissima, Alaria esculenta,
and
Saccorhiza dermatodea
) shows that individual photosynthetic performance reflects
changing light climate in accordance with depth (Bischof et al.
1998b
). Photo-
synthetic acclimation was found for both ambient PAR and UVR. Exposure to
