Divergence among species and populations of Mediterranean pines in biomass allocation of seedlings grown under two watering regimes

Abstract

-Seedlings of four populations each of Pinus pinaster, P. halepensis, P. canariensis and P. pinea were grown in controlled conditions to evaluate both inter-and intra-specific differences in response to watering. We submitted half of the plants to a moderate water stress and after 22 weeks, we recorded height, stem diameter and root, stem and leaves dry weight. Patterns and amounts of phenotypic changes, including changes in biomass allocation, were analysed. We found a scant response in P. canariensis, P. pinaster and P. halepensis presented high population divergence for phenotypic changes, and P. pinea showed marked allocational shifts and no population divergence. The phenotypic changes observed within species are interpreted as a plastic response. The variation encountered within P. halepensis and P. pinaster may be indicative of specialisation to either resource-rich or resource-poor habitats, being populations from favourable sites more plastic. P. pinea exhibited a very uniform plastic response, indicating generalist behaviour.phenotypic changes / early testing / pine / drought stress / ontogeny Résumé -Divergences parmi les espèces et populations de pins méditerranéens pour l'allocation de biomasse chez des semis poussant sous deux régimes d'alimentation hydrique. Des semis de quatre populations de Pinus pinaster, de P. halepensis, de P. canariensis, et de P. pinea ont été élevés en conditions contrôlées pour évaluer au niveau inter-et intra-spécifique les différences de réponse au régime d'alimentation hydrique. Nous avons soumis la moitié des plants à un stress hydrique modéré et après 22 semaines nous avons mesuré leur hauteur, le diamètre de la tige et des racines, le poids sec de la tige et des feuilles. Les modèles et l'importance des changements phénotypiques, incluant les variations d'allocation de biomasse ont été analysés. Nous avons trouvé une faible réponse pour P. canariensis ; P. pinaster et P. halepensis ont présenté une importante divergence des populations au plan des changements phénotypiques, et P. pinea a montré une modification sensible au plan de l'allocation de biomasse sans divergence de population. Les changements phénotypiques observés chez les espèces ont été interprétés comme une réponse en terme de plasticité. Les variations rencontrées chez P. halepensis et P. pinaster peuvent être l'indice d'une spécialisation pour des habitats riches ou pauvres en terme de ressources. P. pinea a présenté une plasticité uniforme de réponse, révélant un comportement généraliste. changements phénotypiques / test précoce / stress hydrique / ontogénie

Phenotypic plasticity in Pinus pinaster δ13C: environment modulates genetic variation

“…The lack of population × year interaction is in accordance with Danjon (1994) who found a stable ranking of the P. pinaster populations for height across years. The absence of a population × site interaction agrees with Chambel et al (2007) who found a non significant population × treatment interaction in P. pinaster seedlings in response to drought stress.…”

Genotype × Environment interactions in Pinus pinaster at age 10 in a multienvironment trial in Portugal: a maximum likelihood approach

“…(i) Differences in phenotypic plasticity among populations, representing an adaptive response to environmental heterogeneity resulting from biotic or abiotic factors. Phenotypic plasticity is under genetic control, has been reported in Maritime pine provenances (Chambel et al, 2007), and was present at the across and within-site level in our study. Population differences in phenotypic plasticity, associated to divergent trends in populations from similar environments, may explain the apparently non-congruent macroenvironments for total height (Fig.…”

“…A high level of phenotypic plasticity for growth and drought tolerance has been reported in several studies (Chambel, 2007;Hopkins and Butcher, 1993;Zas et al, 2004), with Atlantic provenances displaying lower survival under severe water deficits (Alía et al, 1995) or frost stress (Hopkins and Butcher, 1993). Differences in stem form have also been found among populations, mainly explained by differences in competition for light and resistance to snow and wind, with highland populations displaying a better form (González-Martínez et al, 2002;Sierra de Grado et al, 1997).…”

Intraspecific variation in growth and allocation patterns in seedlings of Pinus pinaster Ait. submitted to contrasting watering regimes: can water availability explain regional variation?

“…The number of dwarf shoots was also reduced by drought. The occurrence of dwarf shoots in pine seedlings is a sign of maturity which can be used to evaluate the ontogenetic stage of the seedling (Chambel et al, 2007). Thus, the results from both seedlings' growth and number of dwarf shoots, taken together, suggest that water deficit reduces carbon gain and slows down ontogenetic development in this, like in many other species.…”