Effects of resource availability on condensed tannins and nitrogen in two Quercus species differing in leaf life span

Seedlings of Quercus ilex and Q. cerrioides, an evergreen and a winter-deciduous oak co-occurring in western-Mediterranean forests, were grown at two light regimes (8 and 36% of photosynthetically active radiation), at two water regimes (500 and 800 mm) and with two nutrient availabilities (standard substrate and 7% increase in soil N). The concentrations of soluble condensed tannins (CT) and nitrogen in the leaves were analyzed to test the phenotypic plasticity of these commonly related parameters in two con-generic species with contrasting leaf habit. Q. ilex contains seven times more CT and a few less N than Q. cerrioides. Light increased CT, whereas neither fertilization nor water had an effect on CT. N concentration was decreased by light, increased by fertilization and not affected by water treatment. Plant growth was increased by light but not affected by fertilization or water treatment. CT were negatively correlated with N concentration. CT of the evergreen species exhibited greater plasticity than the deciduous one as reflected by a steeper negative correlation among nitrogen and CT concentrations in Q. ilex. Given the antiherbivory activity of CT, this implies that in less shaded environments, e.g. canopy aperture by disturbances, leaf tissue quality for herbivores will be much more reduced in Q. ilex than in Q. cerrioides. Higher leaf CT in Q. ilex and its higher plasticity to light availability may explain the higher browsing by sheep in Q. cerrioides than in Q. ilex resprouts, as well as the low recruitment rates of seedlings of the former species, reported in other studies.