Team : MEA

PhD student : BAFFOIN Romain

Thesis supervisors :  AMEGLIO Thierry , Lacointe André,  CHARRIER Guillaume

Dates : February 2017 - February 2021

Description 

Predicting frost resistance in trees is a major challenge for selecting species and genotypes adapted to current and future climatic conditions. Currently, two distinct modeling approaches are used. The first approach is based on empirical relationships between frost resistance and temperature and integrates the annual cycle of the tree (the "phenological" model). This approach makes several assumptions, including a close correlation between frost resistance and dormancy. The second approach predicts frost resistance based on physiological variables (interaction between soluble sugar content and water status: the "physiological" model). This less precise but more generic approach has been validated in various organs and species of the walnut tree Juglans regia and Juglans regia x nigra. The objectives of this thesis are therefore to explore the causal relationship between dormancy and frost resistance processes, ii) to demonstrate the genericity of the physiological model on a larger scale and iii) to develop the physiological approach by taking into account the diversity of carbohydrates observed between species. The results obtained showed that frost resistance of trees was dissociated from the dormancy process, the trees having shown a dynamic of acclimatization and deacclimation while they were maintained in endodormancy by cold deprivation. The genericity of the physiological model was demonstrated on a climatic scale (France and Spain). This model has been applied to multiple angiosperm species, but remains unusable in the conifer studied. Adjusting individual parameters for the different soluble sugars and polyols improved its accuracy. The individual effect of each molecule suggests that osmotic regulation is not the only mechanism allowing better frost resistance, but that compartmentalization within tissues and cells could also play a role. The results of this thesis put into perspective the postulates of the phenological model and confirm the relevance of the physiological approach by its genericity integrating environmental, genotypic effects and their interactions. These results open avenues of research for the development of physiological models of frost resistance that will ultimately allow the integration of the effect of summer stress in the frost resistance of angiosperms.

Frost resistance (FH) as a function of the interaction between water content and different expressions of soluble carbohydrates and polyols according to the sum of GFS (A), the sum of SCP (B) or the sum of SCP, each soluble carbohydrate i being weighted by its osmotic potential πi (C) or by a parameter pi fitted by the ISC model (D) calibrated on angiosperm data.

Link

Romain Baffoin, Guillaume Charrier, Anne-Emilie Bouchardon, Marc Bonhomme, Thierry Ameglio, et André Lacointe. Seasonal changes in carbohydrates and water content predict dynamics of frost hardiness in various temperate tree species. Tree Physiology, 2021, 41 (9), pp.1583-1600. ⟨10.1093/treephys/tpab033⟩. ⟨hal-03144794⟩