Ecophysiological traits involved in Corylus avellana response to light conditions

Phenotypic plasticity is considered one of the major means by which plants can cope with the variability of environmental factors. Nevertheless, the extent to which phenotypic plasticity may facilitate survival under environmental condition changes still remains largely unknown. Corylus avellana phenotypic plasticity to shade vs. sun conditions was analyzed in plants growing inside the Natural Reserve Siro Negri (Italy). On the whole the results highlight the successful ability of C. avellana to grow in full sun condition by allocating a high nitrogen (N) content in the form of photosynthetic protein leading to a 10% higher PNUE justifying the more than 100% higher photosynthesis (PN) respect to the shade condition. PN peaks in May and the ratio respiration (RL) /PN shows the lower proportion of carbon respired compared to that assimilated when resources are not limited. Nevertheless, C. avellana grows in shade conditions throughout several adaptations at leaf level which contributes to maximize light capture and reduce carbon loss by respiration resulting in the maintenance of a positive carbon balance. In particular, the more than 100% higher specific leaf area (SLA) in the shade is mainly due to a 20% lower leaf thickness associated to a 44% lower palisade to spongy parenchyma ratio. The analysis of phenotypic plasticity attests C. avellana responsiveness to light variations.The larger plasticity of morphological (PIm= 0.41) than physiological (PIp= 0.36) and anatomical (PIa = 0.24) traits confirms the shade-tolerance of C. avellana. These results suggest that morphological plasticity is more important in shade conditions than physiological plasticity and can be interpreted as a strategy to maximize light capture.