Abstract
Photosynthesis in the communities of various plant spacings in plant bed was tested with ecological methods. From the analysis of dry matter production (Fig. 2, Table 1), field-density effect seemed to appear at the stage when the value of leaf area index exceeded more than 4. From the study of photosynthesis-light curves in plant communities, light satulation was observed even at the stage when the density effect had already appeared (Fig. 3). Changes in the pattern of light curves were not obsered in relation to plant spacings or stage of seedlings. This might be due to the apparent photosatulation by tobacco seedlings in the community, where owing to shading effect whole photosynthesis would be represented by photosynthesis of the surface layer of leaves. Logarithmically linear relation was shown between photosynthesis per unit leaf area and leaf area index (Fig. 4), so the photosynthesis seemed to decrease with the increment of leaf area index. Photosynthesis is decreased in relation to the protein nitrogen content in leaves (Fig. 5), but the decreace in the protein nitrogen content might be due to the reduction in the supply of photosynthate for the protein synthesis. Comparison of leaf number and the ratio of stem dry weight to total dry weight showed that the narrower the spacing of seedling of seedlings, the worse the quality of seedlings became.
