Fróðskaparrit - 01.01.1999, Page 173

VATNPLANTUR í FØROYSKUM VØTNUM VIÐ BLEYTUM VATNI
TAKA LÆTTLIGA ÓLÍVRUNNIÐ KOLEVNIUPP
177
for the more efficient microalgae (Allen
and Spence, 1981).
The alkalinity of the Faroese lakes from
which the plants were collected varied be-
tween 0.16 and 0.37 meqv L'1 (Table 1) and
the concentration of bicarbonate between
0.16 and 0.37 mM (except for one lake with
an alkalinity of 0.8 meqv L"1). These bicar-
bonate concentrations are lower than the
compensation point of most of the tested
species (0.37 mM HC03' is equivalent to a
final-pH of about 10.3). To test whether the
compensation point was affected by alka-
linity, pH drift experiments were performed
at 0.125 meqv L"1 for species found to have
aCCM.
The final-pH at 0.125 meqv L"1 was low-
er than at 1 meqv L"1 (Table 3), which is a
result of the lower, total inorganic carbon
concentration at low, compared to high, al-
kalinity at a given pH. The calculated
HC03" compensation points, which ranged
from 0.12 to 0.03 mM, were also lower at
0.125 meqv L'1 than at 1.0 meqv L"1. The
lower compensation points show that the
CCM species will be able to use HC03'
even at the low concentrations found in the
Faroese lakes. The relative contribution of
HC03" to total inorganic carbon uptake
cannot, however, be estimated from pH-
drift experiments alone.
The inorganic carbon uptake characteris-
tics of aquatic macrophytes are very plastic
within a particular species and change in
response to the availability of inorganic
carbon and other resources. For Elodea
canadensis collected in a range of Danish
lakes and streams the affinity for bicarbon-
ate has been found to vary from high to no
measurable affinity in response to differ-
ences in bicarbonate and C02 concentra-
tions in the water (Sand-Jensen and Gor-
don, 1993). Also, for plants grown in the
laboratory, substantial acclimation in affin-
ity for both HC03' and C02 and in carbon
extraction capacity was observed, not only
in response to C02 and HC03" availability
(Madsen et al., 1996), but also in response
to other environmental parameters (Mad-
sen, unpubl. results, 1998). For the species
collected in this study, however, no correla-
tion was observed between carbon extrac-
tion capacity among species and alkalinity
of water from the collection site, nor was
the distribution of species related to lake al-
kalinity. These results likely reflect the
narrow range in alkalinity found in the
Faroese lakes sampled rather than the lack
of physiological plasticity and responsive-
ness among the species.
Acknowledgement
Funding for this study was provided by The Danish Re-
search Agency, Grant No. 9803000.
References
Allen, E.D. and Spence, D.H.N. 1981. The differential
ability of aquatic plants to utilize the inorganic
carbon supply in fresh waters. New Phytol. 87: 269-
283.
Bain, J.T. and Proctor, M.C.F. 1980. The requirement of
aquatic bryophytes for free C02 as an inorganic
carbon source: Some experimental evidence. New
Phytol. 86: 393-400.
Boston, H.L., Adams, M.S. and Pienkowski, T.P. 1987.
Utilization of sediment C02 by selected North
American isoetids. Ann. Bot. 60: 485-494.
Cole, J.J., Caraco, N.F., Kling, G.W. and Kratz, T.K.
1994. Carbon dioxide supersaturation in the surface
waters of lakes. Science 265: 1568-1570.
Frost-Christensen, H. and Sand-Jensen, K. 1995. Com-
parative kinetics of photosynthesis in floating and