Effects of hydric and light combined stresses on the morphological and plastic responses of Aspidosperma polyneuron Müll. Arg. Seedlings (Apocynaceae)

There is a lack of knowledge on the grow requirements for most endangered plant species in tropical ecosystems. The interdisciplinary field of the “critical zone” provides an opportunity to understand the plant-soil interactions, allowing the development of strategies for species propagation and restoration. Aspidosperma polyneuron is a Tropical Dry Forest native species, currently categorized as “endangered” in Colombia and the neotropics.  In this study, we evaluated the intrapopulation differences in the morphological and plastic responses of A. polyneuron seedlings along an experimental gradient of light and water. We collected seedlings from two locations of the same population at the department of Atlántico (Colombia) and exposed them to three levels of light (100, 55 and 10%) and two different levels of water (field capacity, 60% and dry conditions, 20%). We allowed these seeds to grow for six months in an experimental 3 x 2 x 2 m random factorial design. In addition, we measured 16 morphological and growth traits associated to their performance. Results showed that medium-light treatment produced the most favorable outcome when facing drought conditions, while low light aggravated negative performance effects when facing drought conditions. The seedlings origin was a significant factor influencing the morphological responses of most traits. Regarding plasticity, there were differences in the pattern and magnitude of the traits according to the locality they were collected from. The influence of water gradient prevailed over the light gradient in the phenotypic responses. The results showed differences in the response mechanism of the two groups of seedlings, indicating intrapopulation differentiation processes between both groups.