PREMISE OF THE STUDY: Serotiny, the maintenance of ripe seeds in closed fruits or cones until fi re causes dehiscence, is a key adaptive trait of plants in fireprone ecosystems, but knowledge of phenotypic plasticity for cone retention in woody plants is extremely scarce. On the basis of published literature and our fi eld observations, we hypothesized that increased aridity might decrease the aerial seed bank as a plastic response, not necessarily adaptive.
METHODS: We used a Pinus halepensis common garden replicated in three contrasted sites (mild, cold, and dry) to separate population differentiation from phenotypic plasticity of cone serotiny and canopy cone bank (CCB). Diff erences in growth among trees of the same provenance allowed us to include size effect as a proxy of ontogenetic age for the same chronological age of the trees.
KEY RESULTS: Tree size had a strong negative eff ect on serotiny, but serotiny degree diff ered among trial sites even after accounting for size effects. As hypothesized, serotiny was lower at the harsh (dry and cold) sites compared with the mild site. Genetic variation for size-dependent cone serotiny and significant population × site interaction were confi rmed, the latter implying different plasticity of serotiny among populations. Population diff erentiation for CCB showed an ecotypic trend, with positive correlation with temperature oscillation (continentality) and negative correlation with summer rainfall.
CONCLUSIONS: Growth-limiting environments exacerbated the precocious release of seeds, contrary to the ecotypic trend found for the aerial cone bank, suggesting a counter-gradient plasticity. This plastic response is potentially maladaptive under a scenario of frequent wildfires.