Do leaf traits in two Dalbergia species present differential plasticity in relation to light according to their habitat of origin?

Abstract

The phenotypic plasticity to light of two congeneric species of leguminous trees from distinct habitats was evaluated in a common-garden experiment. For that, we assessed the following two groups of leaf morphological and anatomical traits of 1-year-old seedlings: (1) traits related to light interception (tissues thickness and leaflet mass per area), and (2) traits related to gas exchange (number of leaflets per leaf and measurements of stomatal size and density). Dalbergia nigra (Vell.) Allemão ex Benth. is an endemic Atlantic forest species, and D. miscolobium Benth. is a typical cerrado species. Both were grown under shade and full-sunlight conditions. The phenotypic plasticity of leaves was determined by a relative distance plasticity index (RDPI). For both species, sun leaflets were thicker than shade ones, and only D. nigra presented lower values for stomatal density (nst), percentage of the leaflet area occupied by stomatal pores (nast) and estimated stomatal conductance (gst) under shade conditions. The forest species (D. nigra) had higher plasticity for variables related to gas exchange (number of leaflets per leaf, nst, ast, nast and gst), whereas the cerrado species (D. miscolobium) had higher plasticity for variables related to light interception, such as leaflet mass per area, leaflet thickness and palisade and spongy parenchyma thickness. The degree of plasticity was different for each analysed parameter, and not used to define which species is more plastic. The leaf traits of D. nigra and D. miscolobium that showed high plasticity were related to resources that are not limiting to improve its photosynthesis in a changing light environment.