Vascular Plants
Cavitation occurs in the xylem of vascular plants when the tension of water within the xylem becomes so great that liquid water (of sap) vaporizes locally and dissolved air within the water expands to fill either the vessel elements or tracheids. Plants are generally able to repair cavitated xylem in a number of ways. For plants less than 50 cm tall, root pressure can be sufficient to redissolve air. For larger plants, they must repair cavitation by importing solutes into the xylem via ray cells, or in tracheids, via osmosis through bordered pits; this causes water to enter as well, which can then redissolve the air. In some trees, the sound of the cavitation is clearly audible, particularly in summer, when the rate of evapotranspiration is highest, and can be used to determine the rate of cavitation. Deciduous trees shed leaves in the autumn partly because cavitation increases as temperatures decrease.
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