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Background and Aims: Knowledge of thermal acclimation of physiological processes of boreal tree species is necessary to determine their ability to adapt to predicted global warming and reduce the uncertainty around the anticipated feedbacks of forest ecosystems and global carbon cycle to climate change. The objective of this work was to examine the extent of thermal acclimation of net photosynthesis (An) and dark respiration (Rd) of two distant white spruce (Picea glauca) seed sources (from south and north of the commerial forest zone in Québec) in response to latitudinal and seasonal variations in growing conditions., Methods: The temperature responses of An, its biochemical and biophysical limitations, and Rd were measured in 1-year-old needles of seedlings from the seed sources growing in eight forest plantations along a regional thermal gradient of 5.5 °C in Québec, Canada., Key Results: The average optimum temperature (Topt) for An was 19 ± 1.2 °C and was similar among seed sources and plantation sites along the thermal gradient. Net photosynthesis at Topt (Aopt) varied significantly among plantation sites and was quadratically related to the mean July temperature (MJT) of plantation sites. Topt for mesophyll conductance, maximum electron transport rate and maximum rate of carboxylation were 28, 22 and 30 °C, respectively. Basal respiration rate (Rd at 10 °C) was linearly and negatively associated with MJT. Q10 of Rd (the rate of change in Rd with a 10 °C increase in temperature) did not show any significant relationship with MJT and averaged 1.5 ± 0.1. The two seed sources were similar in their thermal responses to latitudinal and seasonal variations in growing conditions., Conclusions: The results showed moderate thermal acclimation of respiration and no evidence for thermal acclimation of photosynthesis or local genetic adaptation for traits related to thermal acclimation. Therefore, growth of local white spruces may decline in future climates., (© The Author(s) 2017. Published by Oxford University Press on behalf of the Annals of Botany Company.)

Salinized soil productivity in arid and semi-arid regions is steadily decreasing and causing serious environmental and socioeconomic damages. Salix species known to grow under saline stress conditions could provide a viable solution for restoring degraded soil potential. Five Salix species (S. purpurea, S. alba, S. vitellina, S. babylonica, and S. viminalis) endemic to the southern Mediterranean region were grown in hydroponic conditions and assessed for their level of tolerance to salinity. Woody cuttings were treated for 30 days with either 0 or 100 mmol-[L.sup.-1] NaCl. A high interspecific variability was highlighted during treatment as shown by changes in stomata size and density, growth, photosynthesis disruption, and electrolyte leakage. Based on a tolerance index, the five Salix species were ranked in decreasing order for their resistance to salinity: S. purpurea > S. alba > S. vitellina > S. babylonica [greater than or equal to] S. viminalis. These results indicate that some tolerant Salix species could be used as an agroforestry model dedicated to restoration and valorization of soils degraded by salinization. [Journal translation] Key words: salinity, Salix, morphophysiology, interspecific variability, stomatal characteristics. Dans les regions arides et semi-arides, la productivite des sols salinises ne cesse de diminuer causant d'importants dommages socio-economiques et environnementaux. L'utilisation du genre Salix dont plusieurs especes ont montre une aptitude a se developper sous des conditions de stress salin pourrait constituer une solution viable pour la restauration des potentialites des sols degrades. Cinq especes de Salix (S. purpurea, S. alba, S. vitellina, S. babylonica et S. viminalis) originaires de la zone mediterraneenne sud ont ete evaluees en conditions hydroponiques, quant a leur degre de tolerance a la salinite. Des boutures ligneuses ont ete soumises a un traitement salin (100 mmol-[L.sup.-1] NaCl) et un traitement temoin (0 mmol-[L.sup.-1] NaCl) pendant 30 jours. Au cours du traitement, une forte variabilite interspecifique a ete mise en evidence en termes de changement dans la densite et la taille des stomates, de croissance, de perturbation de photosynthese et de fuites d'electrolytes. L'indice de tolerance a permis de classer les cinq especes de Salix selon un ordre decroissant de tolerance a la salinite : S. purpurea > S. alba > S. vitellina > S. babylonica [greater than or equal to] S. viminalis. Ces resultats laissent presager la possibilite de l'utilisation de certaines especes de Salix tolerantes a la salinite comme modele agroforestier dedie a la restauration et a la mise en valeur des sols affectes par la salinisation. Mots-cles : salinite, Salix, morpho-physiologie, variabilite interspecifique, caracteristiques stomatiques., Introduction La salinisation figure parmi les processus environnementaux les plus severes dont les effets directs se manifestent par la degradation de 7 % des terres cultivables a travers le monde [...]

Mesophyll conductance (g m) determines the diffusion of CO2 from the substomatal cavities to the site of carboxylation in the chloroplasts and represents a critical component of the diffusive limitation of photosynthesis. In this study, we evaluated the average effect sizes of different environmental constraints on g m in Populus spp. a forest tree model. We collected raw data of 815 A–C i response curves from 26 datasets to estimate g m, using a single curve-fitting method to alleviate method-related bias. We performed a meta-analysis to assess the effects of different abiotic stresses on g m. We found a significant increase in g m from the bottom to the top of the canopy that was concomitant with the increase of maximum rate of carboxylation and light-saturated photosynthetic rate (A max). g m was positively associated with increases in soil moisture and nutrient availability, but was insensitive to increasing soil copper concentration and did not vary with atmospheric CO2 concentration. Our results showed that g m was strongly related to A max and to a lesser extent to stomatal conductance (g s). Moreover, a negative exponential relationship was obtained between g m and specific leaf area, which may be used to scale-up g m within the canopy. [ABSTRACT FROM AUTHOR]

Climate-related variations in functional traits of boreal tree species can result both from physiological acclimation and genetic adaptation of local populations to their biophysical environment. To improve our understanding and prediction of the physiological and growth responses of populations to climate change, we studied the role of climate of seed origin in determining variations in functional traits and its implications for tree improvement programs for a commonly reforested boreal conifer, white spruce (Picea glauca (Moench) Voss). We evaluated growth, root-to-shoot ratio (R/S), specific leaf area (SLA), needle nitrogen (Nmass), total non-structural carbohydrates (NSC) and photosynthetic traits of 3-year-old seedlings in a greenhouse experiment using seed from six seed orchards (SO) representing the different regions where white spruce is reforested in Québec. Height and total dry mass (TDM) were positively correlated with photosynthetic capacity (Amax), stomatal conductance (gs) and mesophyll conductance (gm). Total dry mass, but not height growth, was strongly correlated with latitude of seed origin (SO) and associated climate variables. Amax, gs, gm and more marginally, photosynthetic nitrogen-use efficiency (PNUE) were positively associated with the mean July temperature of the SO, while water use efficiency (WUE) was negatively associated. Maximum rates of carboxylation (Vcmax), maximum rates of electron transport (Jmax), SLA, Nmass, NSC and R/S showed no pattern. Our results did not demonstrate a higher Amax for northern seed orchards, although this has been previously hypothesized as an adaptation mechanism for maintaining carbon uptake in northern regions. We suggest that gs, gm, WUE and PNUE are the functional traits most associated with fine-scale geographic clines and with the degree of local adaptation of white spruce populations to their biophysical environments. These geographic patterns may reflect in situ adaptive genetic differences in photosynthetic efficiency along the cline. [ABSTRACT FROM AUTHOR]

Tree improvement programs aim to develop families that are well-adapted to future growing conditions. To gain insight into the stability of the family genetic response to climate change, white spruce (Picea glauca) seedlings from 60 full-sib families were subjected to a combination of two temperature regimes and two levels of CO2over two growing seasons. There was positive effect of warmer temperatures and higher CO2on some growth variables but no significant family × treatment interactions. Instantaneous water use efficiency was the only physiological trait that was affected positively by the CO2treatment, showing a 51% increase that was consistent across families. [ABSTRACT FROM PUBLISHER]