Photosynthesis Light Response Curves Research Articles

Calculation of daily totals of the gross CO2 assimilation of leaf canopies.

Daily totals of gross CO2 assimilation of leaf canopies have been calculated, based on photosynthesis-light response curves of individual leaves, and on a set of standard conditions. This work is partly a revision of that by de Wit [see FCA 19, 515 or HbA 36, 357]. It is extended for a range of saturation levels of leaf photosynthesis. The influence of leaf angle distribution is small. A set of descriptive equations is developed that gives an adequate description of the daily totals of gross CO2 assimilation, both of a closed and of a non-closed surface. (Abstract retrieved from CAB Abstracts by CABI’s permission)

A Mobile Apparatus for Measuring Leaf Photosynthesis in the Field

An apparatus is described that has been designed to measure the gas exchange of individual cereal leaves in the field, using infrared gas analysis. Measurements on leaves of winter wheat showed that there was true saturation of net photosynthesis at high irradiances but as irradi ance decreased there was a proportional decrease in net photosynthesis. Measurements made on wheat plants grown in a controlled environment, for comparison, showed the photosynthesis light response curve to be better fitted by a rectangular hyperbola. This dissimilar response of photosynthesis to irradiance for plants grown in controlled environments indicates the possible problems of extrapolation from the laboratory to the field.

Studies on Photosynthesis in Sugar Beet Plant : III. Photosynthesis in the community.

The effect of light on the photosynthesis in the community of sugar beet plants was studied from the view point of intensity of light received by the individual leaves of the community. The results obtained are as follows. (1) Light response curves of photosynthesis in community obtained by calculation on the basis of light intensity on the surface of individual leaves and light response curves of photosynthesis of individual leaves, showed the same tendency as those obtained by direct measurement on photosynthesis of community. (2) These light response curves are light saturation curves, having a saturation point at the horizontal light intensity of ca. 40 Klx. The similar fact is seen in the communities of different leaf area indices (LAI) ranging from 0.9 to 5.6. Light receiving coefficient (ρ) under the incident horizontal light intensity where the photosynthesis shows saturation phenomenon, is lower than 1, and the higher the LAI of community, the lower the ρ. (3) When the horizontal light intensity of incident light becomes higher, some leaves in community receive more and more intense light. However, there remain some leaves on which light intensity does not increase, regardless of the increment of incident light intensity. Even though horizontal light inetnsity gets higher than 30 or 40 Klx, the area of leaves that receive light intensity below the saturation point, does not decrease, and their mean light intensity does not increases either. Consequently photosynthetic rates of these leaves remain at low level. On the other hand, accompanying with the increase of incident light intensity, the photo synthetic intensity of another leaves will become higher untill light intensity of these leaves reaches at saturation point of single leaves. These circumstances cause the light saturation phenomenon in photosynthesis in community. (4) The percentage of leaves whose photosynthetic intensity remains at low level, increases as the LAI of community becomes higher, resulting in the lower ρ in the community of larger LAI.