Alpine Annual Plants: Phenology, Germination, Photosynthesis, and Growth of Three Rocky Mountain Species

E-ISSN： 1939-9170|65|3|759-766

ISSN： 0012-9658

Source： Ecology, Vol.65, Iss.3, 1984-06, pp. : 759-766

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Abstract

Field microenvironments of three annual alpine species, Koenigia islandica, Polygonum confertiflorum, and P. douglasii, were characterized over two growing seasons. Germination, photosynthesis, and growth of all three species were investigated in field and laboratory experiments. The Polygonum species occurred in warm, dry alpine sites which melted out early in the growing season but also dried out early; plants died by mid—August. Koenigia grew in sites which melted out later, but plants remained alive later in the season since their sites did not dry out. Polygonum plants experienced higher soil surface, air, and leaf temperatures than did Kogotus plants. Seeds of the Polygonum species required stratification before they germinated, and light increased germination. Koenigia seeds germinated equally well in light and dark, and stratification was not necessary, although it increased germination percentages. Photosynthetic responses to light were similar in all three species. Koenigia's photosynthetic temperature optimum was lower than those of the Polygonum species (27° vs. 32°C). Maximum net photosynthetic rates (CO₂ uptake of wholeplants) of each species ranged from 12 to 17 μmol°m^—²°s¹. Koenigia plants grew significantly larger and produced more seeds at daytime temperatures of 15° rather than 25° in growth experiments. The reverse was true for the Polygonum species. A single extra week of growth often doubled seed production in these rapidly developing species. Differences in habitat and physiological response probably reflect the evolutionary origins of these species. Koenigia colonized Rocky Mountains from the Arctic, and it inhabits the coolest, wettest, alpine bogs. The Polygonum species appear to have originated at lower elevations in the temperate zone and to have colonized the warmest and driest alpine habitats. The species' photosynthetic, reproductive, and growth responses reflect the conditions in their respective habitats.