Corylus avellana responsiveness to light variations: morphological, anatomical and physiological leaf trait plasticity

Morphological, anatomical and physiological leaf traits of Corylus avellana plants growing in different light conditions within the Natural Reserve “Siro Negri”(Italy) were analyzed. The results highlight the capability of C. avellana to grow both in sun and in shade conditions throughout several adaptations at leaf level. In particular, the more than 100% higher specific leaf area (SLA) in shade conditions is associated to a 44% lower palisade to spongy parenchyma thickness ratio than in sun conditions. Moreover, the chlorophyll a to chlorophyll b ratio (Chl a/b) decreases in response to a 97% photosynthetic photon flux density (PPFD) decrease. The results highlight a decrease in the ratio chlorophyll to carotenoid content (Chla/Cara), the maximum PSII photochemical efficiency (Fv/Fm) and the actual PSII photochemical efficiency (ΦPSII) associated to an increase in the ratio photorespiration to net photosynthesis (Pr/PN) in sun conditions. The multiple regression analysis selects the Chl a/b ratio as the most significant variable explaining PN variations in shade conditions, while in sun conditions the ratio between the fraction of ETR used for CO2 assimilation (ETRA) and that used for photorespiration (ETRp), ΦPSII, nitrogen content per leaf area (Na) and total chlorophyll content per leaf area [Chla (a+b)]. The high phenotypic plasticity of C. avellana (PI =0.33) shows its responsiveness to light variations. In particular, a greater plasticity of morphological (PIm= 0.41) than of physiological (PIp= 0.36) and anatomical traits (PIa =0.24) attests to the shade-tolerance of the species.