Interrelationships between Leaf Amount, Light Distribution and Total Photosynthesis in a Plant Community

Abstract

1. In order to find a practical means of estimation of the production of matter in a plant community and to give a logical explanation to the variability of directly measured values, theoretical analyses have been advanced of the interrelationshipsbetween leaf amount, light distribution and total foliage photosynthesis2. Inside foliage relative light intensity received by the leaves is not always the same as the light intensity measured at horizontal plane at the same height (Fig. 1). In homogeneous stands the former can be derived from Equation (3), when leaf transmissibility is known and extinction coefficient (K in Equation (2)) is obtained beforehand by 'stratifying clip method'.3. If photosynthetic capacity in the active leaf and mean respiration rate of all the leaves in a stand are known, the mean total daily photosynthesis of whole foliage is estimated by Equation (5). An example in representative herbaceous species is presented in Fig. 5, where it is clearly indicated that with lower 'leaf area index' daily production in foliage is indifferent to inclination of leaves, while with increase of leaf amount the role of inclination in the production becomes very remarkable, upright leaves being more efficient than horizontal ones under full daylight as demonstrated by Watson and Witts.4. Compensation light intensity and 'optimum leaf-area index' (Fopt-leaf amount February 1960 SAEKI, T. 63 in the form of LAI for the highest production) are calculated from the photosynthetic capacity in the active leaf and respiration rate of the lower leaf (Equations (6) and (7)). The obtained values seem to be quite reasonable in consideration of the minimum light intensities and 'leaf area indexes' in the natural communities.5. The highest daily production in a plant community, Pmax, calculated with Equation (8) was discussed in relation to the extinction coefficient and incoming radiation (Figs. 7 and 8). An approximate coincidence was recognized between the calculated values and the highest net production in crop fields collated by Blackman and Black.The author should like to express his sincere thanks to Prof. M. Monsi for his