SEASONAL-CHANGES IN PHOTOSYNTHESIS OF YOUNG CRYPTOMERIA-JAPONICA GROWING ON RIDGES AND FOOT-SLOPES

The influence of environmental factors affected by topography, especia lly light conditions in winter, on photosynthetic capacity of field-gr own young Cryptomeria japonica trees was studied. Trees with a large i ncrement in height growth tended to have current year needles with hig h photosynthetic capacity in the growing season. The change in the pho tosynthetic capacity from October to February, corresponding to the ch ange in chlorophyll content, differed between trees planted near a rid ge and on a foot-slope. There was a tendency for trees with a greater exposure to sunshine in winter, such as those near a ridge, to have a reduced chlorophyll content in winter. The photosynthetic capacity of I-year-old needles of sample trees near a ridge did not recover as muc h as those on a foot-slope, even if the foliar nitrogen content was hi gh. These results imply that the magnitude of winter injury on the pho tosynthetic apparatus differed according to the topographical conditio ns and strongly influenced the photosynthetic capacity during the next growing season.