Leaf gas exchange capacity in relation to leaf position on the stem in field grown teak (Tectona grandis L.f.)

Leaf gas exchange patterns in relation to leaf positions on stems were studied in field grown forest tree, teak (Tectona grandis L.f.) during first year growth under intensive culture plantation. Net photosynthetic rates (PN) were low in immature leaves (1-2 from shoot apices), increased basipetally on shoot, peaked in leaves (3rd or 4th leaves from shoot apices) which had recently reached full expansion, and thereafter declined in lower crown leaves. High PN found in fully expanded young leaves was associated with increased dark respiration rate (RD) and high radiation saturation as well as compensating irradiance for PN when compared to those of aged leaves. Intercellular CO2 concentrations (Ci) determined at ambient CO2 concentration and saturating irradiance were apparently low for leaves exhibiting high PN when compared to those of aged leaves. Differences in stomatal conductance (gs) and the rate of transpiration (E) were not apparent between leaves after full expansion. The relationship of PN with Ci recorded for leaves at different positions on stems and under natural ambient CO2 concentrations showed a linear decrease in PN with marked increasing Ci and suggested that increase in mesophyll limitations could cause decline in PN during aging of teak leaves after full expansion. Highly significant positive linear correlation was found between PN and Ci determined at below ambient CO2 concentrations and saturating irradiance for both fully expanded young and aged leaves. The estimate of linear relationship between PN and Ci, often considered as carboxylation efficiency, was higher for fully expanded young leaves characterised by high PN than for aged leaves exhibiting low PN. Hence, the increase in mesophyll limitations or decrease in carboxylation efficiency could explain gradual reduction in photosynthetic potential with leaf age after maturation in teak.