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.) durin g first year growth under intensive culture plantation, Net photosynth etic rates (P-N) were low in immature leaves (1-2 from shoot apices), increased basipetally on shoot, peaked in leaves (3(rd) or 4(th) leave s from shoot apices) which had recently reached full expansion, and th ereafter declined in lower crown leaves. High P-N found in fully expan ded young leaves was associated with increased dark respiration rate ( R-D) and high radiation saturation as well as compensating irradiance for P-N when compared to those of aged leaves, Intercellular CO2 conce ntrations (C-i) determined at ambient CO2 concentration and saturating irradiance were apparently low for leaves exhibiting high P-N when co mpared to those of aged leaves, Differences in stomatal conductance (g (s)) and the rate of transpiration (E) were not apparent between leave s after full expansion. The relationship of P-N with C-i recorded for leaves at different positions on stems and under natural ambient CO2 c oncentrations showed a linear decrease in P-N with marked increasing C -i and suggested that increase in mesophyll limitations could cause de cline in P-N during aging of teak leaves after full expansion. Highly significant positive linear correlation was found between P-N and C-i determined at below ambient CO2 concentrations and saturating irradian ce for both fully expanded young and aged leaves, The estimate of line ar relationship between P-N and C-i, often considered as carboxylation efficiency, was higher for fully expanded young leaves characterised by high P-N than for aged leaves exhibiting low P-N. Hence, the increa se in mesophyll limitations or decrease in carboxylation efficiency co uld explain gradual reduction in photosynthetic potential with leaf ag e after maturation in teak.