Trade-offs among life history and ecophysiological traits underlying population differentiation in Aleppo pine (Pinus halepensis Mill.)

Resumen del trabajo presentado en la 5th International Conference on Mediterranean Pines (Medpine5), celebrada en Solsona (España) del 22 al 26 de septiembre de 2014.As any other living entity, forest trees must optimize resource investment to growth, reproduction and maintenance but investment in one function may occur at the expense of other functions, resulting in trade-offs that limit maximization of all processes. Global Change is imposing new challenges to Mediterranean forests, in particular combined abiotic and biotic stressors such as drought, wildfires and epidemic outbreaks of pests and pathogens. Mediterranean pine populations are expected to harbor a valuable adaptive genetic diversity for facing these challenges, already shaping the populations since long ago. Little is known, however, about how populations will respond to multiple challenges, and about the correlated responses to a single stressor in other life history traits. Common garden experiments with a wide sampling of provenances from the entire distribution range allow us to quantify population differentiation and genetic relationships between key adaptive traits. Our objectives were to determine the intraspecific genetic variation in these key phenotypic traits and to explore the existence of tradeoffs among life history traits. Besides, we also aimed at comparing phenotypic variation with environmental distances between each population source and the trial site as a first step to detect local adaptation patterns.We measured a wide set of traits in 19 provenances of Aleppo pine in a common garden representing average conditions for the species. Traits related to (i) growth and maintenance (height, diameter and bark thickness), (ii) reproduction (cone counts and serotiny level), (iii) constitutive and induced defenses (bio-assay based on a simulated attack) and (iv) water and carbon acquisition and storage (patterns of soil water extraction, water-use efficiency and reserves acquisition dynamics). Results confirmed a strong differentiation among provenances for most assessed variables, and distinct trade-offs between growth and maintenance, reproduction and defense. Contrasting patterns of water and carbon acquisition and storage correlated to phenotypic divergence among populations, indicating different strategies of resource usage. These findings confirm the evolutionary relevance of this approach. In next future, replicated assessment across contrasting sites will help understanding how climate change might modify the patterns of phenotypic integration obtained in a single site.Peer reviewe