Náttúrufræðingurinn - 1983, Page 42

SUMMARY
The effect of climate on grass
growth and development
by
Aslaug Helgadóttir,
The Agricultural Researclt Institute,
Keldnaholti,
110 Reykjavík.
Ecologically contrasting populations of
Poa pratensis L. and Agrostis tenuis Sibth.,
collected from old fertilizer experiments in
Sámsstadir and Akureyri, Iceland and
Rothamsted, England, as well as from
natural sites of high altitude in Iceland,
were compared in spaced plant trials in
Reading, England and at Korpa, Iceland.
A number of morphological characters
was recorded over a period of three
years. In the present paper only three are
reported; winter survival, heading date
and reproductive ratios.
Winter survival of all populations of
both species was adequate at Reading. At
Korpa, on the other hand, winter survival
of British populations of A. tenuis was
poor. Survival of British populations of P.
pratensis was better, though not as good as
that of Icelandic populations of both spe-
cies. Differences between populations are
related to their climatic origin, whereas
differences between species are related to
contrasting growth habits.
Heading occurred earlier in P. pratensis
than in A. tenuis at both Reading and
Korpa. When grown at Reading, the natu-
ral populations of P. pratensis from Gull-
foss and Skálafell headed first, followed by
the British populations, which were closely
followed by the other Icelandic popula-
tions. At Korpa, the natural populations
headed slightly before the other Icelandic
populations, but the British populations
headed much later. In contrast to P.
pratensis, all the Icelandic populations of
A. tenuis headed much later than the Brit-
ish populations at Reading and vivipary
was observed in some of the Icelandic
populations. At Korpa, heading occurred
more or less simultaneously in the Ice-
landic populations. These results indicate
that the critical photoperiod for floral
initiation is much longer in A. tenuis than
in P. pratensis. The differences in floral
development of the contrasting popula-
tions are again related to their climatic
origin.
Populations of P. pratensis from
Rothamsted had larger reproductive ratios
at Reading than at Korpa, populations
from Sámsstadir had larger ratios at
Korpa, while populations from Akureyri,
Gullfoss and Skálafell had similar ratios at
both sites. The sporadic flowering in
populations of A. tenuis from Sámsstadir
and Akureyri resulted in fairly low repro-
ductive ratios at Reading. The populations
from Skálafel! and Gullfoss had, on the
other hand, much higher ratios when
grown at Reading than when grown at
Korpa. The reproductive ratios of the con-
trasting populations reflect the severity of
their native habitat, but are though influ-
enced by the ability of the two species to
reproduce vegetatively.
It is concluded that growth and develop-
ment of the contrasting populations re-
flects the seasonal pattern of climatic
variation, particularly photoperiod and
temperature, in their native habitat.
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