In closed canopies, the photosynthetic capacity decreases from top to bottom. This decrease is interrelated with an exponential decrease in light intensity with increasing overlying LAI, a decrease in R/FR ratio and increasing leaf age. In many crop systems, increasing age and decreasing light intensity occur simultaneously for individual leaves: effects of aging and decreasing light intensity are inherently interacted. To separate these effects on the photosynthetic capacity of leaves, tomato plants were forced to grow horizontally, to guarantee always the same light intensity for all leaves on a plant. Experiments were done in a climate-controlled greenhouse compartment under natural light conditions in winter and spring. In winter no difference in Photosynthetic capacity was measured in leaves ranging from 20 to 70 days old. In spring, however, photosynthetic capacity decreased almost linearly with leaf age (20 -70 days old). In winter, the daily light integral was fairly stable while in spring the daily light integral increased almost linearly. Plotting the photosynthetic capacity against the light integral over three weeks during leaf growth resulted in a linear relation. This suggests that the light integral during leaf growth and expansion plays a role in the formation of the photosynthetic capacity. We suggest that in upright stands the decrease in photosynthetic capacity from top to bottom could also partly be explained by the effect of the natural light conditions during the growth phase of the leaves. Logically this effect should be mostly visible during increasing daily light conditions as it is in spring.
|Publication status||Published - 2007|