Biology Reference
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nutrients all year-round, and growth of algal species inhabiting the Antarctic is
considered to be light-driven. This main difference in nutrient availability drives
the internal regulation and strategies of light harvesting and nutrient assimilation.
Although there are no kelps in the Antarctic, kelp-like Himantothallus grandifolius
(Desmarestiales) is endemic to the Antarctic and dominates large coastal areas, but
its growth is largely restricted to the ice-free months in spring (Drew and Hastings
1992 ; see also Chap. 13 by Wiencke and Amsler). On the other hand, the kelp
Laminaria solidungula , endemic to the Arctic, stops its growth during N-depleted
summer and accumulates carbon skeletons that are used for growth later in winter
when N becomes available (Henley and Dunton 1995 ). According to Korb and
Gerard ( 2000 ), L. solidungula can be considered a “storage specialist” for nitrogen
assimilation. Its high V max for nitrate uptake, coupled with low growth rates, allows
Arctic plants to take advantage of seasonally elevated concentrations and accumu-
late large internal pools of nitrate and organic N-reserves. In the Antarctic,
H. grandifolius does not accumulate nitrate, so that N-uptake characteristics are
better adapted to optimize energy consumption rather than N-assimilation. Prefer-
ential use of NH 4 þ over NO 3 displayed by H. grandifolius (but not by
L. solidungula ) would add evidence of an energy-saving strategy (Korb and Gerard
2000 ; see also Chap. 2 by G´mez and Huovinen, Chap. 13 by Wiencke and
Amsler). It is then expected that these two different strategies will ultimately
determine their ability to face a given environmental change.
Traditionally, it was thought that this seasonal growth pattern observed in Arctic
kelps was a direct consequence of N availability (Chapman and Lindley 1980 )as
well as light availability (Henley and Dunton 1997 ). However, it has become
apparent that, at least in some species, this pattern is under the control of an
endogenous free-running circannual rhythm entrained by a critical minimum
daylength in autumn (L
uning 1994 ). This suggests
that the addition of nitrate-N to summer N-limited kelps would have only
a marginal effect on growth and biochemical composition, presumably due to the
prevailing internal clock (Henley and Dunton 1997 ). Gordillo et al. ( 2006 ) con-
firmed that the effects of nutrient enrichment on biomass composition play only
a marginal role in a number of species from Kongsfjord (Svalbard). When thalli of
21 species were collected in summer and incubated for 2 days under nitrate and
phosphate enrichment, the C:N ratio was only affected by 7% on average. Lack of N
accumulation and enhanced photosynthetic ability is in agreement with the internal
clock prevailing over external nutrient conditions, which in summer would promote
active photosynthesis over nutrient use.
uning 1991 ; Schaffelke and L
4.4 Different Ways of N Utilization
Sources of N for macroalgal growth are mostly in the form of nitrate and ammonium,
and the metabolism of inorganic N by algae is known to be regulated by both N forms
(Solomonson and Barber 1990 ). Furthermore, different species show different
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