KEEPING WARM 
the silversword plant ( Argyroxiphium 
sandwicense) on the volcano Haleakala 
in Hawaii. 
Each growing season, alpine and arc- 
tic plants must quickly produce green 
leaves capable of fast rates of photosyn- 
thesis. We have measured, both in the 
field and under controlled conditions, 
net photosynthetic rates of Oxyria from 
many arctic and alpine populations 
across a wide span of temperatures, 
from near freezing to as high as 1 13°F. 
Almost universally, arctic ecotypes had 
higher rates of photosynthesis than did 
alpine ecotypes, and rates were highest 
in plants grown at the lowest tempera- 
tures. Oxyria plants grown at the high- 
est temperature, on the other hand, 
could carry on photosynthesis at higher 
temperatures than plants of the same 
ecotypes grown at lower temperatures. 
Alpine ecotypes can acclimate to tem- 
perature changes more quickly and pre- 
cisely than can arctic ecotypes, which 
indicates that photosynthetic acclima- 
tion is under genetic control. In alpine 
regions, where temperatures near the 
ground fluctuate rapidly with changes 
in sunlight and wind, a plant capable of 
quickly adjusting its photosynthetic sys- 
tem to fit the moment would be at an 
advantage. Temperatures in the Arctic 
are more steady and predictable, so an 
acclimation mechanism would be of less 
benefit there. 
As plants carry on photosynthesis, 
starch grains accumulate in the chloro- 
plasts. During the night, this starch is 
converted to sugar, which is moved out 
of the leaf chloroplasts into the stem and 
roots. Chabot found that even during 
the cold nights characteristic of an al- 
pine summer, chloroplasts in Oxyria 
plants from the Sierra Nevada could 
make this conversion of starch to sugar. 
In contrast, chloroplasts in leaves of 
Encelia virginensis, a desert shrub spe- 
cies that grows a bit farther down the 
east slope of the Sierra, could not con- 
vert starch to sugar if subjected to these 
same cold nights. After only a few days 
and nights, the accumulated starch 
broke up the Encelia chloroplasts, 
thereby damaging the photosynthetic 
system. 
All arctic and alpine plants are 
adapted to metabolizing and reproduc- 
ing at low temperatures. The local vege- 
tational patterns that are particularly 
characteristic of alpine regions, how- 
ever, are caused by other aspects of the 
environment. These factors could be 
persistent snowdrifts, rock types, nutri- 
ents, or water availability. For example, 
the upper windward side and ridgetop of 
a slope lose water because strong winds 
blow their snow into drifts on the lee 
side. These snowbanks last well into the 
summer and supply snow meltwater to 
moist meadows and wet bogs lower 
down the slope. The local distribution of 
alpine species is closely related to this 
type of soil moisture gradient. Some 
species are present in all parts of the 
gradient except under snowbanks that 
melt very late or that melt completely 
only in unusually warm and dry sum- 
mers; those places are bare. Most spe- 
cies, however, exist only in certain parts 
of the moisture gradients: dry ridgetops, 
moist meadows, or wet bogs. Thus the 
use of water by these plants or their 
resistance to drought is as important to 
their survival as their ability to grow in a 
cold environment. 
When sufficient water is not available 
to alpine plants, metabolism slows down 
markedly in some species but not so 
much in others that are adapted to get- 
ting along with less water during dry 
periods or in drier sites. Steven Ober- 
bauer and I studied water use by plants 
along an alpine moisture gradient in the 
Medicine Bow Mountains of Wyoming 
and found that each species is unique 
with regard to water intake, retention or 
loss of water, and tolerance to water loss 
from leaves. On the dry ridge, shallow- 
rooted species tend to be conservative in 
water use; deep-rooted species, such as 
moss campion and Parry’s clover ( Trifo- 
lium parry i), may use and lose more 
water by obtaining it from deeper in the 
soil. Wet-meadow plants, in contrast, 
tend to lose considerable water. 
Oxyria differs from most other plants 
in its water use, having little or no ability 
to hold water or withstand drought. In 
the mountains throughout western 
North America, the species is confined 
to rocky places below or near snow- 
banks. Oxyria roots must have a good, 
reliable source of water because its 
leaves lose water easily, and it will con- 
tinue to lose water every day until the 
water source dries up. Not surprisingly, 
Oxyria never becomes established in 
drought-susceptible places; on the other 
hand, it is a poor competitor in the 
densely vegetated wet meadows. This is 
one reason Oxyria is so site-specific, is 
not abundant, and seldom grows with 
other plants along the topographic mois- 
ture gradient. 
Another factor determining local dis- 
tribution of plant species in alpine and 
arctic locations is the ability to obtain 
and utilize certain mineral nutrients in 
places where such nutrients are in short 
supply. Nitrogen and phosphorus, for 
example, tend to be the nutrients least 
available in cold soils. More is known 
about the nutrient requirements of 
plants in arctic tundra, where the cold 
soils over permafrost are low in nutri- 
ents, than in alpine regions. Most of our 
knowledge in this regard is due to the 
work of F. Stuart Chapin III, and his 
colleagues at the University of Alaska, 
on the availability and absorption of 
phosphorus by water sedge ( Carex 
aquatilis), a widespread arctic-alpine 
species that occurs from the High Arc- 
tic to the southern Rocky Mountains. 
Chapin has studied the relation of phos- 
phorus to this species along a latitudinal 
gradient extending from Point Barrow, 
Alaska, to the high mountains of central 
Colorado. In each of five locations, he 
found that water sedge was restricted to 
colder soils than those occupied by other 
sedge species. Under standard labora- 
tory conditions, water sedge ecotypes 
collected from the coldest, most phos- 
phate-deficient soils demonstrated 
higher phosphate absorption rates than 
did ecotypes from more favorable sites. 
This compensation in absorption rates, 
Chapin concludes, is primarily a re- 
sponse to phosphate availability rather 
than to soil temperature. 
Many of the factors that influence 
distribution also affect the different 
methods of reproduction found in cold- 
climate plants. In general, there is a 
latitudinal gradient from alpine regions, 
where reproduction by seeds is the com- 
mon method, to cold, wet arctic tundras, 
where only a few species produce seeds 
regularly and the dominant plants repro- 
duce vegetatively. This appears to be a 
reflection of the warmer microclimates 
and drier conditions in the high moun- 
tains of the middle latitudes and tropics. 
The flat, cold tundras of the north are 
not favorable — in temperature, length 
of growing season, or nutrients — to the 
production of seeds. In the Arctic, even 
those species that do reproduce by seeds 
take several years longer to reach the 
seed-producing stage than the same spe- 
cies farther south. 
In the wet tundras, most species of 
grasses and sedges reproduce vegeta- 
tively, by rhizomes. Water sedge, for 
example, and most of the grasses and 
sedges associated with it in the tundra 
near Point Barrow produce seeds only 
rarely. Some sedges and grasses at Bar- 
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