Leaf physiological and structural plasticity of two Asplenium (Aspleniaceae) species coexisting in sun and shade conditions

Background and aims – Relatively few studies have addressed the sun-shade response of fern species. Moreover, there is no information on species-specific plasticity patterns of such response, their relationship with species ecological requirements and the costs of such plasticity. The present study aims at filling these gaps by analysing the sun-shade plastic response of two Asplenium species that differ in their ecological requirements. Methods – We measured 27 leaf morphological, anatomical and physiological parameters using standard methods for A. ceterach and A. trichomanes in the field. The parameters were combined through Principal Component Analysis in order to highlight an integrated sun-shade response across species. Linear regression analysis was carried out to highlight the relationship between the calculated species plasticity patterns and the structural control on photosynthetic process. Key results – A significant degree of phenotypic plasticity was found for both species. Moreover, sun and shade leaves shared a common slope for the morpho-functional relationships reflecting no additional costs in terms of carbon assimilation. Even if the plastic responses of the two species scaled positively (R2 = 0.68, P = 4.667e‒07), A. trichomanes was characterized by a slightly higher anatomical plasticity (plasticity index = 0.19), while A. ceterach showed a higher physiological plasticity (0.60). Conclusion – A remarkable acclimation capacity for the two Asplenium species in response to different light conditions was highlighted. Nevertheless, A. ceterach seems to be more suited to cope with full sunlight conditions as compared to A. trichomanes, according to species ecological requirements.