KEEPING WARM 
Arctic and alpine ecotypes of the 
same species are often quite distinct. 
This alpine sorrel in the Wyoming 
Rockies cannot photosynthesize as 
fast at low temperatures as a plant 
of the same species in the Arctic. 
William Dwight Billings 
have found the concept of the ecotype to 
be very useful. In 1922, Swedish bota- 
nist Gote Turesson found that within 
widely distributed plant species, certain 
local populations evolved tolerances to 
different kinds of environments. When 
grown together in his garden under uni- 
form conditions, these populations, 
which he called ecotypes, maintained 
their distinctive appearance and 
flowering characteristics. Genetically 
distinct entities adapted to a given 
type of environment within the range 
of a species, ecotypes may be evolution- 
ary dead ends or, by isolation through 
time, they may become species in their 
own right. 
In the last twenty-five years, studies 
of the physiological traits of arctic and 
alpine species and their ecotypes have 
produced the greatest advances in ef- 
forts to understand plant adaptations to 
cold-summer climates. For more than 
twenty years, a number of researchers, 
including H.A. Mooney of Stanford 
University, M.M. Caldwell of Utah 
State University, B.F. Chabot of Cor- 
nell University, RG. Godfrey of the 
University of Massachusetts, and I have 
been working with alpine sorrel (Oxyria 
digyna ), a widely distributed, but not 
abundant, arctic-alpine species. In 
ecotypes of this species, photosynthesis 
and flowering are closely tied to tem- 
perature and to intensity and duration of 
sunlight. The arctic ecotypes are quite 
distinct from the alpine ecotypes in form 
and structure (for example, the usually 
horizontal underground stems called 
rhizomes are present in all arctic popu- 
lations and absent from western Ameri- 
can alpine populations), but I shall con- 
centrate here on just a few of the 
physiological adaptations we have 
found. These principally involve the 
ways in which certain plant processes 
are affected by solar radiation and tem- 
perature. 
Almost all arctic and alpine plants are 
perennial and take two or more years 
after seed germination to reach flower- 
ing age. Oxyria is no exception. After 
growing very slowly for two or three 
years, many of these plants produce, at 
ground level, a bud containing pre- 
formed floral initials that overwinter 
and bloom very soon after the following 
summer’s thaw. In Oxyria, the breaking 
of dormancy in such flower buds de- 
pends primarily on two developments: 
first, the bud temperature must rise 
above freezing, and second, day length 
must have reached the maximum num- 
ber of hours attainable at the latitude at 
which the population grows. Oxyria 
plants in the Medicine Bow Mountains 
of Wyoming won’t bloom until day 
length has reached fifteen hours and 
those in the Olympic Mountains of 
Washington (latitude 48° north) must 
have a sixteen-hour day, while alpine 
sorrel on the North Slope of Alaska 
(latitude 71° north) or at the same lati- 
tude in Lapland requires the continuous 
daylight of an arctic summer. At arctic 
latitudes, however, optimum day length 
comes before thaw and lasts long after 
it. Hence Oxyria plants there wait until 
July to bloom, even though by that time 
the sun has been continuously above the 
horizon for several weeks. 
Another way that sunlight particular- 
ly affects alpine plants involves ultravio- 
let B radiation, the shortest wavelengths 
of solar ultraviolet light that can pene- 
trate the atmosphere and reach the 
earth’s surface. High mountains have 
less atmosphere above them, so the 
amount of such ultraviolet radiation 
reaching alpine plants is more than that 
reaching the leaves of plants at sea level. 
Also, stratospheric ozone, which is 
somewhat of a shield against ultraviolet 
B radiation, is much thinner and less 
dense over equatorial regions than over 
polar regions; thus, high mountains in 
the tropic and even in the temperate 
zones receive much more ultraviolet ra- 
diation than does the Arctic. Caldwell 
found that relatively little ultraviolet 
radiation gets through the leaf epider- 
mis of alpine Oxyria and several other 
species of alpine plants and that a bit 
more penetrates the leaf epidermis of 
arctic Oxyria plants. He also measured 
greater epidermal transmission of ultra- 
violet radiation in green Oxyria leaves 
than in leaves that the pigment 
anthocyanin had turned purple or red. 
The anthocyanin acts as a screen against 
penetration of ultraviolet to the photo- 
synthetic tissues of the leaf. Caldwell 
discovered experimentally that ultravio- 
let injury to the leaves of some alpine 
plants, including Oxyria, can be re- 
versed by exposure to certain wave- 
lengths of visible light. The absence of 
visible ultraviolet damage in nature 
probably means that under normal al- 
pine conditions such photorepair mecha- 
nisms are constantly at work. Early in 
the season, for example, when ultravio- 
let irradiance is high and many kinds of 
plants emerging from melting snow are 
whitish due to a lack of chlorophyll, 
young shoots often develop a bright red 
color as they synthesize anthocyanin 
from sugars stored in the roots from the 
previous summer. Some alpine plants, 
however, produce little or no anthocya- 
nin in the leaves. In such cases, the 
ultraviolet is usually absorbed by other, 
colorless compounds and/or is reflected, 
as Caldwell and his colleagues found in 
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