POLISH POLAR RESEARCH
20
3
291-299
1999
Adam BARCIKOWSKI1'3 and Paweł M. LORO 23
Department of Plant Ecology and Nature Conservation
Institute of Biology and Environmental Conservation
Nicolaus Copernicus University
Gagarina 6
87-100 Toruń, POLAND
e-mail: [email protected]
2
Department of Plant Ecology
Institute of Biology and Environmental Protection
Teachers Training College
Żołnierska 14
10-561 Olsztyn, POLAND
Department of Antarctic Biology
Polish Academy of Sciences
Ustrzycka 10
02-141 Warszawa, POLAND
Changes in chlorophyll content throughout the year
in selected species of mosses on King George Island,
South Shetland Islands, maritime Antarctic
ABSTRACT: A tall moss turf dominated by Polytrichastrum alpinum, a moss carpet composed
of Sanionia uncinata and S. georgico-uncinata, and a moss hummock with Brachythecium
austro-salebrosum were investigated on King George Island in the maritime Antarctic. Changes
in chlorophyll (a+b) content throughout the year are described. Clearly seasonal development of
plants, as concerns their chlorophyll content, was not noted. The highest mean values of chloro­
phyll content were obtained from Sanionia georgico-uncinata moss (5.14 mg g' dry weight DW), then in Brachythecium austrosalebrosum (4.55 mg g'1 DW) and slightly lower in Sanionia
uncinata (4.47 mg g"' DW). The least mean values of chlorophyll content were obtained from
Polytrichastrum alpinum (2.34 mg g"' DW).
Key words: Antarctica, King George Island, mosses, chlorophyll.
Introduction
Mosses, next to the lichens, are a major component of the vegetation on the
ice-free areas of the maritime Antarctic. 104 species of mosses and 24 species of
liverworts are known from that region (Ochyra and Vafia 1989, Ochyra et al. 1998,
Lewis-Smith 1984). In the land ecosystems of King George Island, mosses some-
292
Adam Barcikowski and Paweł M. Loro
times represent more than 90% of the biomass of the plant community (Barci­
kowski and Oleksowicz 1989). Their distribution of patterns are correlated with
the habitat conditions, which are also strongly influenced by colonies of penguins
(Tatur et al. 1997). Different sub-formations of spore-producing plants with differ­
entiated eco-physiological parameters of production develop as a consequence of
abiotic and biotic influences.
The present studies, conducted in 1996, are a continuation of field studies in
the eco-physiology of mosses initiated by Zarzycki and Barcikowski (1993) in the
area of Admiralty Bay. The studies concerned the content of chlorophyll in four
species of mosses dominating in the plant communities, differentiated by their hab­
itat conditions.
The study was completed during the XXth Antarctic Expedition organized by
the Department of Antarctic Biology, Polish Academy of Sciences.
Materials and methods
The research area was situated in the vicinity of the Polish Antarctic Station
Arctowski.
In this area three sampling points were chosen: these represented fragments of
different sub-formations of Antarctic tundra spore-producing plants identified ac­
cording to Lindsay (1971), Furmańczyk and Ochyra (1982), Ochyra (1984, 1998)
and Longton (1988). They included:
1. Moss hummock sub-formation established by Brachythecium austrosalebrosum (Mull. Hal) Kindb., present on banks of streams with a rapid flow of water.
2. Tall moss turf sub-formation dominated by Polytrichastrum alpinum (Hedw.)
G. L. Sm.
3. Moss carpet sub-formation dominated by Sanionia uncinata (Hedw.) Loeske and Sanionia georgico-uncinata (Mull. Hal.) Ochyra and Hedenas. The species
differed in their preferred habitat conditions. Sanionia georgico-uncinata occu­
pied flat, wet areas with visibly flowing water. S. uncinata occupied drier places
on a slightly declining slope; water conditions here were subject to significant
changes during the year - during thawing and after rainfall the slope was very wet
while during the drier seasons it dried out significantly. Sanionia georgico-unci­
nata was partly occupied by a parasite fungus Thyronectria antarctica (Speeg.)
Seller var. hyperantarctica Hawksw. (Olech 1992). Parallel measurements were
carried out in plants free of the fungus and those occupied by the fungus in order to
assess the influence of Thyronectria antarctica upon the decrease in chlorophyll
content in Sanionia georgico-uncinata.
From each of the sampling points 5 samples of a given species of moss were
collected during the austral summer in weekly intervals; from April till June and
from October till November the samples were collected every two weeks, and dur-
Chlorophyll content in mosses
293
ing the wintertime (from July through October) once a month. Between June and
October it was sometimes impossible to take a proper sample because of the thick
snow cover. Samples were taken using metal rings of 3.16 cm in diameter
(7.84 cm2). From each sample 200 mg of green biomass (tops of stems) were taken
for determination of chlorophyll (a + b) content. The remaining part from each
sample served for the determination of water content in the plant. It was weighed
with the accuracy of 0.001 g, dried (at 80°C ) to a constant mass, and weighed
again. The content of chlorophyll (a + b) was measured using the method described
by Śestak (1971) using a Spekol spectrophotometer after previously calibrating the
apparatus with chlorophyll a + b. The statistical analyses presented in the paper
were conducted using Tblcurve software by Jandel, while the graphs are presented
using Excel software.
Results
Chlorophyll content in Brachythecium austrosalebrosum
The average content of chlorophyll in top sections of stems of Brachythecium
austrosalebrosum during the year was 4.55 mg g"1 DW, whereas the range was rel­
atively wide (from 1 to 7.5 mg g"1 DW). Changes in the chlorophyll content in rela­
tion to dry weight not indicate a clear seasonality (Fig. 1). A weak seasonal trend
was observed in the relation of chlorophyll content to fresh weight (Fig. 2). High
chlorophyll content in fresh weight was maintained during the summer period
(from 18 January till 14 March). The period preceding the peak summer season
(from 28 December till 11 January) was characterised by a lower content of chloro­
phyll, similar to observations done for the austral summer. In winter samples were
not collected because the thick layer of snow. Throughout the year the water con­
tent of tissues maintained roughly a constant level (Fig. 2). Studies on the relation
between the water content of tissues and the content of chlorophyll in dry weight
indicated a slight increase in chlorophyll content with the increase in water content.
The curve describing this relation may be represented by the formula: y = a + bx +
ex2, (R2 = 0.38). The same comparison relating to the average chlorophyll content
in fresh weight shows a close correlation y - 8.85 - 0.15x + 0.00068x2 (R2 = 0.62).
The effect of dilution described by Więckowski (1960), representing a relative de­
crease in the percentage of chlorophyll content with the increase in water content in
the tissue, also becomes visible.
Chlorophyll content in Polytrichastrum alpinum
Changes in chlorophyll content in the case of Polytrichastrum alpinum during
the year, converted to dry weight (Fig. 1) and fresh weight as well as the level of
water content in tissues (Fig. 3), indicate a relatively constant year-round level of
chlorophyll. The average content of chlorophyll was 2.34 mg g"1 DW with a mini-
dry weight
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mum content of 1 mg g"1 DW and a maximum content of 3 mg g"1 DW. The chloro­
phyll content in relation to fresh weight varied within a narrower - range from 0.4
to 1.2 mg g"1 fresh weight. A decrease was observed in chlorophyll content after
the winter season (after 30 October) and in samples collected from under snow
(29 June). During such periods an increase in water content of tissues was ob­
served. Analysis of the relation between the chlorophyll content and the level of
295
Chlorophyll content in mosses
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Fig. 3. Chlorophyll and water content in 1 g fresh weight in Polytrichastrum alpinum.
water content in tissues in relation to dry weight indicates a slight increase in chlorophyll content with the increase in the water content of tissue (the fitting of the
curve y = a + bx + ex2 was R2 = 0.26). Similar analysis concerning the fresh weight
does not show a correlation as well.
Chlorophyll content in Sanionia uncinata
Changes in chlorophyll content during the year in relation to dry weight of
Sanionia uncinata were characterised by a relatively high amplitude (Fig. 1), however, they did not show any seasonal trend. The average content of chlorophyll was
4.47 mg g"1 dry weight, reaching a minimum value of 1.8 mg g"1 and the maximum
value of 7.5 mg g"1 DW. Similar to Polytrichastrum a lower content of chlorophyll
may be observed in samples collected from under the icy snow during the winter
period (from 29 June till 30 October) and also in summer after periods of a temperature decrease (28 December, 4 and 18 January, 8 and 15 February and 14 March).
Significantly wider variations in chlorophyll content were observed in its relation
to fresh weight (Fig. 4). During the summer season (samples dated 4 and 11 January and 1 and 8 February), after intense rainfall or snow melting, the chlorophyll
content increased beyond the range of normal variations. Comparing the data on
the water content in the tissues we see an almost mirror reflection. An increase in
water content of tissues was accompanied by a decrease in chlorophyll content (the
earlier mentioned "dilution effect"). A linear dependence was identified between
water content of tissue and chlorophyll content in fresh weight described by the
function y = bx, (R2 = 0.77). There is no clear dependence between water content
of tissues and the chlorophyll content in relation to dry weight.
296
Adam Barcikowski and Paweł M. Loro
Date of measurement
-chlorophyll content and standard deviation
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Fig. 4. Chlorophyll and water content in 1 g fresh weight in Sanionia uncinata.
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Fig. 5. Chlorophyll and water content in 1 g fresh weight in Sanionia georgico-uncinata.
Chlorophyll content in mosses
297
Chlorophyll content in Sanionia georgico-uncinata
The dynamics of chlorophyll content in Sanionia georgico-uncinata related to
its dry weight throughout a year were similar to S. uncinata, showing a large amplitude of changes without a clear seasonal trend (Fig. 1). This species showed the highest average chlorophyll content (5.14 mg g"1 DW) among all the mosses studied. The
minimum content of chlorophyll in a sample was 2 mg g"1 DW while the maximum
was reached at over 9 mg g"1 DW. The amplitude of changes in chlorophyll content
in relation to fresh weight was significantly wider (Fig. 5) and was linked to the level
of water content in the tissues. The course of the chlorophyll content curve, similar to
that for S. uncinata, is a mirror image of the curve of water content changes. The detailed analysis of the relation between chlorophyll content and water content of tissues indicates a close negative correlation in relation to dry weight (y = a + bx3, R2 =
0.77). A similar analysis concerning fresh weight does not show any correlation.
Changes in chlorophyll content of Sanionia georgico-uncinata caused by a
parasitic fungus Thyronectria antarctica
In a significant part of the studied area Sanionia georgico-uncinata, the dominating species in moss carpet sub-formation, was infested mainly by a parasitic
fungus Thyronectria antarctica. In comparison with non-infested patches, the
patches of moss infested with fungus were more tawny in colour. The fungus
caused clearly visible changes in their leaf tissue, leading to their necrosis. Significant changes in colour in the studied site were observed from the beginning of
March. Losses in chlorophyll content were observed from mid-March through the
end of May, i.e. the first snow coverage. The percent of loss in chlorophyll content
in tissues infested by the fungus was presented in Fig. 6. Losses in chlorophyll content {a + b) ranged between 32% and 55%. The seasonal differences found were insignificant as they were within the limits of statistical error.
Discussion
This paper presents the yearly dynamics of chlorophyll content (a + b) calculated
in relation to the dry weight and fresh weight of four species of mosses. The highest
chlorophyll content in dry weight was recorded in Sanionia georgico-uncinata (5.14
mg g"1 DW), followed by Brachythecium austrosalebrosum (4.55 mg g"1 DW), and
still slightly lower by Sanionia uncinata (4.47 mg g"1 DW). The lowest average chlorophyll content was found in Polytrichastrum alpinum (2.34 mg g"1 DW).
The obtained values of chlorophyll content are significantly higher than those
obtained by Russell (1985) for mosses of Marion Island, where the chlorophyll content was 0.143 mg g"1 DW for Ditrichum strictum (Hook.f. and Wils.) Hampe and
1.357 mg g"1 DW for Brachytecium rutabulum (Hedw.) B., S. and G. Chlorophyll
content in the tissues of studied mosses was also slightly higher than the values ob-
298
Adam Barcikowski and Paweł M. Loro
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Fig. 6. Decrease in chlorophyll content in Sanionia georgico-uncinata moss due to Thyronectria
antarctica parasitic fungus.
tained for mosses from the temperate climate zone, where the average chlorophyll
content was from 0.83 mg g"1 DW for Aulacomium palustre (Hedw.) Schwaegr. to
6.39 mg g"1 DW for Pleurozium schreberi (Brid.) Mitt. (Barcikowski and Zbigniewicz 1992, Barcikowski 1996). It seems that these high values of chlorophyll content
in mosses of King George Island resulted from the natural fertilisation of the plant
habitats with the organic matter produced by penguins (Tatur et al. 1997).
The results obtained confirm the rule described by Rastorfer (1972) followed
by Lewis Smith (1984), that mosses occupying wet habitats in maritime Antarctica
have 2-3 times more chlorophyll than species from relatively dry locations. Rela­
tively insignificant decreases in the chlorophyll content after the winter also con­
firm the opinion expressed by Brown and Hooker (1977) and Hooker (1977) fol­
lowed by Lewis Smith (1984), that extended periods of freezing of Antarctic
mosses have little influence upon their chlorophyll level.
Acknowledgements. — The authors would like to express their gratitude to Prof. Dr.
Ryszard Ochyra, from W. Szafer Institute of Botany, Polish Academy of Sciences, for his assis­
tance in correct identification of the studied species of mosses.
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Received February 2, 1999
Accepted May 11, 1999
Streszczenie
W czterech gatunkach mchów dominujących w zbiorowiskach roślinnych King George Island
(South Shetland Islands) zbadano dynamikę roczną zawartos'ci chlorofilu (a+b) oraz wody. W anali­
zowanych gatunkach nie stwierdzono wyraźnych zmian badanych parametrów powiązanych ze
zmianami sezonowymi. Największą średnią zawartość chlorofilu w ciągu roku stwierdzono u Sanionia georgico-uncinata (5.14 mg g' suchej masy), mniejszą u Brachythecium austrosalebrosum
(4.55 mg g' s.m.) i nieco mniejszą u Sanionia uncinata (4.47 mg g' s.m.). Najmniejszą średnią
zawartość chlorofilu w ciągu roku stwierdzono u Polytrichastrum alpinum (2.34 mg g"1 s.m.).