Physiological and Ecological Analyses of Shade Tolerance of Plants

In order to analyse the shade tolerance of plants on the basis of dry matter production, the growth of green-gram plants was examined under varying light intensity (full daylight, 75, 50, 30 and 20% light) in the early stages of growth, and their responses to shading were determined.1. The growth of total plant weight was depressed very markedly by heavy shading (30 and 20%), while the growth in 75% light followed closely that in full light.2. The leaf growth decreased in dry weight with increasing shading, but it showed in area an optimum in 50% light rather than in full light. Heavy shading caused remarkable depression of leaf growth not only in weight but also in area.3. The relative growth rate (RGR) increased with increasing light intensity in the early stage of the experiment (August 14-20), while in the late stage (August 27-September 3) the RGR was a little higher in 75, 50 and 30% light than in full light.4. The net assimilation rate (NAR) generally decreased with increasing degree of shading. As the plants grew, the NAR was reduced progressively in all the plots with diminished plot differences.5. The leaf area ratio (LAR) tended to be small with increasing light intensity. The ratio of leaf weight to total plant weight (F/W) was decreased a little by shading, while the ratio of leaf area to leaf weight (F/F) increased markedly, especially in the deep shade. Thus the LAR, which was expressed by the product of F/W and F/F, became larger as shading increased.6. Positive effect of nutrient supply was observed, only in full light and in light shade, on the growth in plant weight, leaf weight and leaf area. On the F/W and F/F ratio, however, there was no significant effect of nutrient supply.