Seasonal pattern of photosynthetic production in a subalpine evergreen herb, Pyrola incarnata.

Abstract

The seasonal pattern of growth and matter production of Pyrola incarnata, an evergreen herb on the forest floor in subalpine deciduous forests, was analyzed to understand the ecological significance of evergreenness in a subalpine climate with a short growing season and low temperature. Net production was highest under favorable light conditions in spring after the disappearance of snow cover, and 68% of the annual net production was attained before the canopy tree foliage had fully expanded. Most of the photosynthetic production in this period was carried out with over-wintered leaves. This appears to be an advantage of evergreenness. New leaves and inflorescences had developed in the period. Positive net production was maintained under deteriorating light conditions during summer, when 32% of the annual net production occurred. This production was used mainly for growth of fruits and underground organs. The net production of P. incarnata during summer was much higher than that of a related species that inhabits warm-temperate regions, because of its higher photosynthetic activity rather than its lower respiratory losses. The storage of dry matter in leaves and underground organs was not conspicuous. Unlike the warm-temperate species and another subalpine species that inhabits higher altitudes, P. incarnata is not strongly dependent on its reserve matter for the development of new organs.