Freezing dynamics and injury in overwintering buds

Winter survival of woody plants depends on tiny but highly specialized structures: overwintering buds that protect future leaves, flowers, and shoots. As climate change disrupts seasonal temperature cues, plants are increasingly faced with damaging freezing events at times when buds have not yet developed sufficient cold hardiness, or are already dehardened. Buds exhibit highly diverse architectures, but how their structure and chemistry govern freezing survival remains poorly understood, limiting our ability to predict freezing damage and breed resilient species. This project addresses a central hypothesis: freezing survival in buds is determined by structural ice barriers, freeze-induced dehydration dynamics, and biochemical traits - factors that have been largely overlooked due to methodological and conceptual limitations. We propose that species- and tissue-specific freezing injury arises from two distinct mechanisms: either intracellular ice formation or critical freeze-induced dehydration. Identifying which mechanism dominates in different bud types is essential for understanding freezing vulnerability in a warming climate. Using woody species grown under contrasting temperature regimes, we will link cold hardiness to bud architecture, water relations, and biochemical composition. High-resolution thermal methods will test whether small tissue size and extensive freeze dehydration produce low- temperature freezing events that escape detection by conventional techniques, and whether freeze-induced water movement can be quantified to refine existing freezing typologies. We further hypothesize that ice formation is not random, but confined to specific extracellular regions whose location and capacity depend on bud structure and morphology. The project will also examine how specialized ice barriers prevent ice intrusion into supercooled meristems. Structural features such as cell wall composition, cell arrangement, lipids, phenolics, and pectins, as well as seasonal accumulation of fructans, are expected to regulate water efflux and stabilize supercooling. Finally, we will test whether freezing injury is best predicted by the degree of freeze dehydration rather than the occurrence of a lethal freezing event, and whether membrane failure marks the lethal threshold. By integrating thermal analysis, microscopy, spectroscopy, and metabolomics, this research provides a mechanistic foundation for understanding bud cold hardiness. The outcomes will improve frost-risk prediction, guide breeding of cold-resilient crops and trees, and strengthen forecasts of ecosystem stability and biodiversity shifts under climate change.