Genotypic variation in photosynthesis in cacao is correlated with stomatal conductance and leaf nitrogen
A. J. Daymond | P. J. Tricker | P. Hadley
Variation in photosynthetic parameters was observed between eight contrasting cacao (Theobroma cacao) genotypes. Net photosynthetic rate (PN) ranged from 3.4 to 5.7 μmol(CO2) m-2 s-1 for the genotypes IMC 47 and SCA 6, respectively. Furthermore, genotypic differences were detected in quantum efficiency ranging from 0.020 to 0.043 μmol(CO2) μmol-1(photon) for UF 676 and AMAZ 15/15, respectively. Differences in PN were correlated with both stomatal conductance (gs) and leaf nitrogen per unit area. Some variation in water use efficiency was observed between genotypes, both intrinsic (PN/gs) and instantaneous (PN/transpiration rate). Both measures of water use efficiency were a negative function of specific leaf area. Evidence was found for a trade-off mechanism between cacao genotypes in photosynthesis and leaf structure. High photosynthetic rate, expressed on a mass basis was associated with smaller leaves. Furthermore, thinner leaves were compensated for by a higher nitrogen content per unit mass.
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