Mechanism of wetwood formation in silver fir (Abies alba Mill.)

Wetwood is a common phenomenon in silver fir (Abies alba Mill.), posing technical challenges for its industrial use. In this study, we thoroughly characterized the properties of this particular wood, investigating the mechanisms governing its formation and exploring its potential physiological relevance for trees. To address these objectives, we used a wide range of techniques, offering a comprehensive insight into the structure of wetwood at different scales, from cellular to whole-tree. Our results revealed significant variability in moisture distribution in the heartwood of the silver fir trees studied, suggesting the absence of a predefined distribution pattern. The physical properties of wetwood differ from those of sapwood, notably in terms of its hydraulic conductivity, which is null. In addition, our study demonstrated that the anatomical characteristics of wetwood are identical to those of normal dry heartwood, including features such as aspirated tori in bordered pits and the absence of nuclei. These results suggest a normal initial duraminization process followed by a progressive resaturation of the heartwood of silver fir. Taken together, these observations strongly suggest that the water present in wetwood is trapped and unavailable for use by the tree, particularly under conditions of prolonged drought.