Abstract
As part of a program to select maritime pine (Pinus pinaster Ait.) genotypes for resistance to low winter temperatures, we examined variation in photosystem II activity by chlorophyll fluorescence. Populations and families within populations from contrasting climates were tested during two consecutive winters through two progeny trials, one located at a continental and xeric site and one at a mesic site with Atlantic influence. We also obtained the LT50, or the temperature that causes 50% damage, by controlled freezing and the subsequent analysis of chlorophyll fluorescence in needles and stems that were collected from populations at the continental trial site. P. pinaster showed sensitivity to winter stress at the continental site, during the colder winter. The combination of low temperatures, high solar irradiation and low precipitation caused sustained decreases in maximal photochemical efficiency (Fv/Fm), quantum yield of non-cyclic electron transport (ΦPSII) and photochemical quenching (qP). The variation in photochemical parameters was larger among families than among populations, and population differences appeared only under the harshest conditions at the continental site. As expected, the environmental effects (winter and site) on the photochemical parameters were much larger than the genotypic effects (population or family). LT50 was closely related to the minimum winter temperatures of the population's range. The dark-adapted Fv/Fm ratio discriminated clearly between interior and coastal populations.In conclusion, variations in Fv/Fm, ΦPSII, qP and non-photochemical quenching (NPQ) in response to winter stress were primarily due to the differences between the winter conditions and the sites and secondarily due to the differences among families and their interactions with the environment. Populations from continental climates showed higher frost tolerance (LT50) than coastal populations that typically experience mild winters. Therefore, LT50, as estimated by Fv/Fm, is a reliable indicator of frost tolerance among P. pinaster populations.
Highlights
Pinus pinaster progeny trials have been established throughout Spain for conservation purposes and to analyze the growth and physiological adaptations of different seed sources to several soil and meteorological conditions [1]
Natural populations have been subjected to selection by their particular set of local environmental conditions and may differ in performance when grown at a common site
Populations were arranged according to the bioclimatic index (Table 1): Arenas and Tamrabta, the populations from continental climates, followed by Oria from south Spain, are subjected to more stressful conditions at their sites of origin, similar to those experienced at the xeric site
Summary
Pinus pinaster progeny trials have been established throughout Spain for conservation purposes and to analyze the growth and physiological adaptations of different seed sources to several soil and meteorological conditions [1]. These trials were designed with a nested structure to examine families within populations. Natural populations have been subjected to selection by their particular set of local environmental conditions and may differ in performance when grown at a common site. Progeny trials are the best way to evaluate the genetic value of selected parents to determine the population best suited to particular climatic conditions. The populations and families evaluated here have shown differentiation and plasticity in growth and physiological parameters related to drought, such as carbon isotope composition [3], vulnerability to xylem embolism [4] and accumulation of phytoregulators [5]
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