This project examines how desert plants avoid exceeding the limits of their water transport system. Water is lost by evaporation when plants capture carbon dioxide from the atmosphere during photosynthesis. To support continued growth, such losses must be replenished by water pulled from the soil via the roots to the leaves in a manner not unlike drinking from a straw. If the suction driving water movement becomes to great, as can happen when the evaporation rate from leaves is too high or the soil is too dry, the plant's water transport system can become non-functional. This condition, known as cavitation, results from the entry of air into the vascular system producing an air embolism and interrupting the movement of water. The limits of the water transport system, and hence the plants maximum drought tolerance, are determined by the structure of its component conduits. The proposed research will determine the limits on water transport in plants from habitats with different patterns of water availability. The ability of each species to maintain water transport by remaining within the limits of its vascular system or controlling the loss of vascular function under harsh conditions will be evaluated. The results will advance our understanding of whole plant responses to water stress.
