The survival and growth of woody plants in dryland regions of the United States depends on their ability to withstand tissue dehydration during drought. It is particularly important that the cells specialized in transporting water (xylem vessels) from the soil to leaves remain functional and that the water column not be disrupted by air bubbles (embolism). In higher plants the introduction of air bubbles into xylem vessels results in a blockage of water transport and, if extensive enough, kills the plant. Laboratory experiments indicate that one of the major cases of xylem embolism is severe water stress during extended periods of drought. However, very little is known about the occurrence and significance of embolism in nature. No data are available for dryland plants where tissue water stress is great and thus where embolism may be the most significant. The objective of this proposed study is to provide the first information on the role of xylem embolism in plant growth, productivity, and survival of dryland plants, specifically chaparral shrubs indigenous to California. This project will shed light on the dynamics of water relations in chaparral vegetation, especially during the early phases of recovery after wildfire. This knowledge could potentially lead to an improved management of chaparral as a water shed, as a deterrent of soil erosion/landslides as a cove for wild animals and as a browse for livestock.
