Water activity in seed and pollen banks: an efficient tool to improve conservation of forest genetic resources

Water activity in seed and pollen banks: an efficient tool to improve conservation of forest genetic resources. Genetic diversity of forest reproductive materials, in combination with environmental effects, induces significant intra-specific phenotypic diversity of materials like pollen and seed lots. This makes it difficult to predict the moisture behaviour of forest reproductive material and consequently complicates management procedures. We built and analysed numerous sorption isotherms to describe the moisture behaviour of forest tree seed and pollen lots. As expected, we obtained moisture behaviour models and, more advantageously, optimal equilibrium relative humidity (eRH) values for seed and pollen storage. Water activity (aw) measurement is a non destructive, portable and rapid technique to assess moisture content. Both aw and eRH are reliable indicators of the status of water in compounds like seeds or pollen because they are a function of the water potential (Ψ), or energy status of water in hygroscopic matrixes. Gravimetric moisture content (MC) of a given sample is not a factor but a consequence of the combination of water potential and the variable amounts of hygroscopic (starch, proteins) and non hygroscopic (lipids) components. Moreover, sorption isotherms reveal a significant intra-specific variability of resulting MC for a given aw, seriously weakening the operational prediction and use of gravimetric moisture content from eRH. Water activity assessment appears to be a reliable moisture monitoring technique for materials having high phenotypic variability; it results, for a given species, in reproducible moisture management procedures based on single recommended aw values. Therefore, aw will be a useful tool for improving the conservation of diversity.