Fróðskaparrit - 01.01.1999, Blaðsíða 170

174
HIGH INORGANIC CARBON EXTRACTION CAPACITY OF SUBMERGED
MACROPHYTES FROM SOFTWATER FAROESE LAKES
Table 2.
List of species included in this study. Altemative
inorganic carbon sources that can be exploited by
the dijferent vascular plants and macroalgae are
listed. Abilitv to use sediment-CO was extracted
from Spence and Maberly (1985) and Richardson
et al. (1984) and the ability to exploit the
atmospheric C02 pool was diagnosed from the
ability to develop floating or aerial leaves.
Talva 2
Yvirlit yvir sløgini, sum henda kanning fevnir um.
Listi yvir aðrar ólívrunnar kolevniskeldur, sum tær
ymisku leggstreingjaplantumar og makroalgumar
fáa nýtt. Spence og Maberly (1985) og Richardson
et al. (1984) komu fram á, hvussu væl plantumar
vóm førar fyri at nýta C02 úr botnsetingini, og alt
eftir, hvussu tær megnaðu at menna flóti-ella
luftbløð, varð mett um, hvussu væl tær vóm førar
fyri at nýta C02-puljuna í luftini.
Species Alternative
Carbon Source
Callitriche stagnalis Atmosphere
C. hamulata Atmosphere
Eleocharis acicularis Atmosphere
Fontinalis antipyretica
Isoetes lacustris Sediment
Juncus bulbosus
Littorella uniflora Sediment
Lobelia dortmanna Sediment
Myriophyllum altemiflorum
Nymphaea alba Atmosphere
Polygonum amphibium Atmosphere
Potamogeton alpinus Atmosphere
P. filiformis
P. gramineus Atmosphere
P. natans Atmosphere
P. obtusifolius
P. perfoliatus
P. polygonifolius Atmosphere
P. praelongus
Sparganium angustifolium Atmosphere
Utricularia vulgaris
Chara sp.
Cladophora sp.
Nitella sp.
Spirogyra sp.
Vaucheria sp.
3). Calculated and expressed as the per-
centage of the inorganic carbon pool ex-
tracted from the water, Isoetes had removed
less than 1%, whereas Vaucheria had re-
moved more than 57%.
The differences in extraction capacity
among plants are believed to reflect differ-
ences in their inorganic carbon uptake
mechanisms. For species with low extrac-
tion capacity, the data are consistent with
diffusive entry of C02 and C-3 physiology.
In contrast, species with high extraction ca-
pacity are expected to employ some kind of
carbon concentrating mechanism. Of these
mechanisms, active uptake of bicarbonate
constitutes the most efficient system in
terms of inorganic carbon extraction capac-
ity among submerged macrophytes (Mad-
sen and Sand-Jensen, 1991). Whether
plants rely on diffusive entry of C02 and C-
3 photosynthesis or use a carbon concen-
trating system cannot be determined from
final-pH alone. However, from final-pH
and alkalinity of the incubation medium,
the C02 compensation point of the plants
can be calculated and compared to C02
compensation points reported in the litera-
ture, which vary from about 1.5 pM to more
than 100 pM (Maberly and Spence, 1983).
For plants incubated in a medium with an
alkalinity of 1.0 meqv L"1 at 10 °C, as in
this study, a compensation point of 1.5 pM
will allow the plants to raise pH to about
9.2. Using this value to separate species
with and without the ability to operate a
CCM, the data in Table 3 show that 14 of
the 26 species tested had this ability. Table
3 also shows, however, that the pH drift
data do not offer a marked distinction be-