The intraspecific trade-off between photosynthesis and phenolics in selected crop species: a meta-analysis study

Phenolics are multifunctional secondary metabolites taking part in both the defence against biotic and the protection against abiotic stress factors. At the interspecific level the concentration of leaf phenolics is negatively correlated with net photosynthesis: Plant species with inherently high photosynthetic rates (mainly annuals) are characterized by low phenolic pool, whereas slow growing species (mainly perennials) show the opposite trend. Crop plants represent a special case of the first group because they have been bred to maximize photosynthesis at the expense of defence and protection. We conducted meta-analyses in four selected crop plants (tomato, pepper, cucumber and olive) in order to test if the trade-off between photosynthesis and phenolics is valid at the intraspecific level as well. We observed that all plants are able to accumulate phenolics under conditions that reduce photosynthesis. However this negative correlation shows different characteristics, pending on the individual species. Moreover, both the basic and maximum level of phenolics in olive leaves is higher than the corresponding ones of the other species. The present investigation indicates that the trade-off between photosynthesis and phenolics at the intraspecific level reflects the answer given by each plant species against the growth–defense/protection dilemma.