Effect of leaf age and shading on photosynthesis in potatoes (Solanum tuberosum)

The effects of leaf age and of shading on photosynthetic rate and on other leaf parameters of potato (Solanum tuberosum L.) were studied using a portable gas exchange system. A rapid decrease in the rate of photosynthesis during leaf senescence was observed. This was accompanied by an increase in stomatal resistance, and as a result a fairly constant level of sub-stomatal CO₂ concentration was maintained at all leaf ages. The reduction in the photosynthetic rate in older leaves was therefore assumed to be essentially mesophyllic in origin, whereas the stomatal response was probably secondary.Canopy density significantly affected the rate of photosynthetic reduction with leaf age. Leaves maintained under high radiation intensities manifested a slower decline in their photosynthetic rate, especially in the early stages of their senescence, than leaves kept under shade conditions. The latter leaves were found to be more adapted to low radiation intensities, as indicated by changes in their chlorophyll a:b ratio and specific leaf weight