Leaf light-saturated photosynthesis for wild and cultivated peach genotypes and their hybrids:: A simple mathematical modelling analysis

We measured leaf photosynthetic activity, stomatal conductance and leaf carbohydrate reserves (soluble sugars and starch) for seven peach genotypes of different introgression level, i.e. commercial varieties, Prunus davidiana and genotypes derived from Prunus davidiana. In early May, branches of each genotype were girdled and leaf to fruit ratio treatments were applied to obtain contrasting source-sink ratios. Photosynthetic activity was significantly different between treatments. We adjusted an asymptotic curve (monomolecular) to the strong relationship between light-saturated photosynthesis (A(sat)) and stomatal conductance (g(s)). This monomolecular curve appeared to be independent of genotype and year. Thus, one unique value for the maximum of A(sat) (A(max)) and one unique value for the initial increase rate of A(sat) per unit of g(s) (q) were estimated (A(max) = 20.68 mumol m(-2) s(-1) and q = 83.73). Leaf reserves (soluble sugars and starch) became significantly larger for low crop loads than for high crop loads, whatever the genotype. Genotype effect on soluble sugars and starch concentrations was limited. Low A(sat) appeared to be correlated with a high accumulation of leaf reserves. A three-parameter curve was used to describe the relationship between photosynthesis activity and leaf reserves. Values of the parameters of this relation appeared to be independent of genotype and year. Practical considerations on source-sink conditions and experimental treatments are recommended.