Comparison of the photosynthetic responses to temperature and light of Betulamaximowicziana and Betulaplatyphylla var. japonica

Abstract

Betula maximowicziana Regel and Betulaplatyphylla var. japonica Hara are common early successional tree species in Hokkaido. The CO2 exchange rates of early and late leaves in the sunny crown of 10-year-old trees were investigated in relation to leaf growth. The green period of the leaves of B. platyphylla was 10–15 days longer than that of B. maximowicziana. Net photosynthesis of both species attained a maximum toward early July, declined temporarily in early August, and decreased from late September, when the daily minimum temperature fell below 10 °C. The optimal temperature for net photosynthesis in both species ranged between 10 and 20 °C, under a photosynthetic photon flux density of 525 μE•−2•s−1; however, net photosynthesis of B. maximowicziana declined more rapidly above this optimum, as compared with B. platyphylla. The inflection point of the relationship between temperature and respiration rates of both species occurred around 15 °C in early leaves, and around 20 °C in late leaves. The light compensation point at 20 °C of B. maximowicziana was 18.7 μE•m−2•s−1; that of B. platyphylla was 30.3 μE•m−2•s−1. The stronger pioneer species characteristics in B. platyphylla, as compared with B. maximowicziana, are indicated by its higher light utilization and its wider optimal temperature range for photosynthesis.