Nutrio-physiological studies on the tomato plant III. Photosynthetic rate of individual leaves in relation to the dry matter production of plants

Abstract

The apparent photosynthetic rate at 70 klux of a leaf attains a peak (33-46 mg CO₂-dm^-3.hr^-1) at a very early stage of its development, decreases rapidly, and then maintains a low constant value (5mg CO₂.dm^-3.hr^-1). The photosynthetic rate is positively correlated with the content of nitrogen, phosphorus, chlorophyll and starch, and is negatively correlated with the content of calcium, manganese, silicon, and moisture. However, the physiological significance of these correlations is doubtful. The photosynthetic potential exceeds the requirement of the sink as a whole plant. The surplus of photosynthates of young, upper leaves is considered to depress the photosynthetic activity of old, lower leaves. This is a conceivable reason for the rapid decline of photosynthetic activity of a leaf with age. A low but constant photosynthetic rate (5mg CO₂.dm^-3.hr^-1) of old leaves at later stages is due, most probably, to a gradual increase in the weight of these leaves. The leaves lower than L₆ are considered to be the source for roots, and the photosynthetic rate of these leaves remains higher (10 mg CO₂.dm^-3.hr^-l than the upper leaves.