Abstract
The growth of Sasa nipponica (Makino) Makino and Sasa borealis (Hack.) Makino on the floor of deciduous forest on the south slope of Mt. Asama was analyzed from seasonal changes of light intensity in the forest and of their leaf area indeces, and light response curve of photosynthesis in both Sasa plant leaves. The relative light intensity below the deciduous forest canopy had a seasonal change following a curve that reached a bottom in summer and showed a plateau from late autumn to spring. The light condition at habitat of S. borealis in the forest was far less favourable than that of S. nipponica. The biomass of S. nipponica increased with increasing light intensity, while that of S. borealis increased with decreasing light intensity in the deciduous forest. The photosynthetic light response curve of S. borealis followed a pattern as generally shown in shade leaf (a low Pmax and low light saturation point). The leaf area index of S. nipponica increased in summer and decreased in winter, while that of S. borealis was almost constant throughout the four seasons. From the facts mentioned above, it can be said that S. nipponica has a higher productivity at the outside than inside of the deciduous forest, while S. borealis can keep a comparably high productivity even inside the forest. Therefore, the habitat isolation of both Sasa species may have been caused by the interspecific difference in dry matter production.
