Embolism in the xylem of plants is the presence of air- filled xylem conduits (tracheids and/or vessels) and it can lead to a significant reduction in water transport capacity. This in turn can adversely influence the water balance of the plant causing reduction of growth and dieback. In a preliminary study of embolism in sugar maple (Acersaccharum) trees in northern Vermont, Sperry and Tyree found that during the winter the xylem of saplings became over 70% embolized, with many small twigs losing all of their water conducting capacity to embolism. Gradual recovery from winter embolism occurred during the spring and was associated with the development of positive xylem pressures. In their proposed research, Sperry and Tyree will determine how widespread the phenomenon of winter embolism and recovery is in co-occurring tree species representing ring-and diffuse-porous angiosperms, and conifers. This will be done in the context of year-round monitoring of embolism levels for each species over the period of funding. Through field and laboratory manipulations they intend to determine the causal link between environmental conditions and the induction of embolism, as well its reversal. This information will guide them in assessing how important xylem embolism is in the ecological tolerance of tree species, and in explaining episodes of species dieback and decline. This research may have important consequences for silvicultural practices, including the establishment of plantations and management of existing stands, especially in regions where winter injury is prevalent. By determining the mechanism of embolism induction, this research will also evaluate how important embolism is in the influence of environmental stress on tree health.
