Chlorophyll and nitrogen contents were highest in leaves of middle position, similarly as photosynthetic efficiency represented by 14C fixation (maxima in leaf 5 from the top). All the leaves lost 14C after 2 weeks of 14CO2 exposure. However, the reduction in radioactivity was less in young upper leaves than in the mature lower leaves. Leaves exported 14C-photosynthates to stem both above and below the exposed leaf. Very little radioactivity was recovered from the seeds of plants in which only first or second leaves were exposed to 14CO2 implying thereby that the carbon contribution of first two leaves to seed filling was negligible. The contribution of leaves to seed filling increased with the leaf position up to the sixth leaf from the top and after the seventh leaf their contribution to seed filling declined gradually. and Desiraju Subrahmanyam, V. S. Rathore.
High variability in leaf gas exchange and related traits were found in 30 genotypes of field grown finger millet. The variability in carbon exchange rate per unit leaf area (PN) can be partly attributed to the differences in the stomatal conductance (gs) and area leaf mass (ALM). The PN was positively correlated with total dry matter (TDM). However, no relationship between PN and seed yield was found. The leaf area showed a positive and significant correlation with total biomass. None of the other gas-exchange traits had significant relationship either with TDM or with seed yield. The ALM showed a strong positive association with PN. However, it was not correlated with either total biomass or seed yield. As a result, the use of ALM as surrogate for PN for identifying high biomass producing genotypes only had a limited value. Hence selection for high PN would result in higher biomass producing types.
Influence of manganese (Mn) toxicity on photosynthesis in ricebean (Vigna umbellata) was studied by the measurement of gas exchange characteristics and chlorophyll fluorescence parameters. The net photosynthetic rate (PN), transpiration rate (E), and stomatal conductance (gs) were reduced with increasing Mn concentration in nutrient solution. The reduction in gs and E was more pronounced at 6 d of Mn treatment. However, PN declined at 2 d of Mn treatment implying that the reduction in photosynthesis was not due to the direct effect of Mn on stomatal regulation. Mn did not affect the maximum efficiency of photosystem 2 (PS2) photochemistry (Fv/Fm). A reduction in photochemical quenching (qP) and excitation capture efficiency of open PS2 (Fv'/Fm') with a concomitant increase in qN was observed. This implies that reduced demand for ATP and NADPH due to the reduction in photosynthesis causes a down-regulation of PS2 photochemistry and thus a high pH gradient (increase in qN) and limited electron transport (decreased qP). and Desiraju Subrahmanyam, V. S. Rathore.
Variability in leaf gas-exchange traits in thirteen soybean (Glycine max L. Merr) genotypes was assessed in a field experiment conducted at high altitude (1 950 m). Leaf net photosynthetic rate (PN) exhibited a high degree of variability at all the growth stages studied. PN and other gas-exchange parameters exhibited a seasonal pattern that was similar for all the genotypes. PN rate was highest at seed filling stage. PN was positively and significantly associated with aboveground dry matter and seed yield. The area leaf mass (ALM) exhibited a strong positive association with leaf PN, aboveground dry matter, and seed yield. The positive association between ALM, PN, and seed yield suggests that this simple and easy to measure character can be used in breeding programmes as a surrogate for higher photosynthetic efficiency and eventually higher yield.