Biology Reference
In-Depth Information
1997
; Wiencke et al.
2009
). Interestingly, algae from cold regions have exploited
very efficiently the potential for LICF as a strategy to minimize the carbon losses
due to high respiration and to optimize the supply of carbon skeletons during rapid
growth during the short open water season (Drew and Hastings
1992
;G
´
mez and
Wiencke
1998
) (see below). For example, in the kelp-like Antarctic brown alga
Ascoseira mirabilis
, LICF represents approximately 9.5% of light C-fixation
(G
´
mez et al.
1995a
,
b
), which is comparable to ratios found in species of
Lami-
naria
(Kuppers and Kremer
1978
) (Table
2.1
). Despite the potential for LICF that
seaweeds exhibit, it is not clear whether this pathway may compensate for C losses
due to respiration as pointed by Kremer (
1981
). Thomas and Wiencke (
1991
) did
not conclusively demonstrate its relationship with dark respiration in several
Antarctic marine algae. In general, LICF was between 4.9 and 31% of dark
respiration in five brown algae and one red alga. In species such as
Himantothallus
grandifolius
and
Desmarestia anceps
, low LICF values were coupled with high
respiration rates (Thomas and Wiencke
1991
). This situation confirms the findings
reported in
Ascophyllum nodosum
where a net C loss due to respiration was
estimated in the dark (Johnston and Raven
1986
). Recent studies revisiting the
role of LICF in carbon metabolism of seaweeds have demonstrated that these
reactions can be functional to morpho-physiological strategies to cope with, e.g.,
enhanced solar UV radiation. In blades of
Lessonia nigrescens
, LICF decreased
70% whereas light carbon fixation decreased by 90% under elevated doses of UV-B
radiation. This suggests that LICF could be regarded a compensating mechanism
necessary to keep physiological performance of algae during severe photodamage
(G
´
mez et al.
2007
). The findings that LICF is also well expressed in temperate and
polar Rhodophytes such as
Cryptopleura lobulifera
,
Palmaria decipiens
, and
Iridaea cordata
(Thomas and Wiencke
1991
; Weykam
1996
; Weykam et al.
1997
; Cabello-Pasini and Alberte
1997
) open questions related with its involvement
in morpho-functional processes that allow these organisms to cope with stressful
conditions. Involvement of LICF as a mechanism to reduce photorespiration has
only been reported in the Chlorophyte
Udotea
(Reiskind et al.
1988
). For most of
seaweed groups, especially green and red algae, data on LICF are lacking and thus
further studies are required in order to outline accurate conclusions on the signifi-
cance of this pathway for the ecology of seaweeds.
2.5 Morpho-functional Aspects of Carbon Metabolism
Carbon metabolism in seaweeds is integrated in multicellular organization that in
many groups exhibits several plant-like traits. Although seaweeds do not display
the structural complexity of vascular plants, the integration of form and function is
an important factor even in the simplest groups, e.g., uncorticated filaments and
sheet-like species. Thus, gross morphology of seaweeds has been related with
ecophysiological adaptations (especially photosynthetic performance and carbon
production) in response to abiotic and biotic determinants (Littler and Littler
1980
;
