Vascular plants transport water from roots to leaves in a highly specialized hydraulic system, the xylem. Most of the time, water in this system is under sub-atmospheric or negative pressure, which creates the possibility that air can be sucked into the conducting cells through leaks, forming air bubbles. These air bubbles, which are called xylem embolisms, can impede water transport in plants, in severe cases leading to death of roots, branches, or whole plants. In many plants, embolisms form even under mild drought stress, frequently even daily. Many plant species have been found to have the ability to remove air bubbles from the xylem and refill the conducting cells with water even while the xylem is still transporting water under negative pressure. Other species appear to be unable to repair embolism under negative pressure. The aims of this project are to test for embolism repair in seed plant species ranging from a grass to conifer trees, relate the findings to anatomical traits of the xylem, and test for cellular mechanisms used by these species to remove air and refill the hydraulic system. The research is designed to test alternative hypotheses regarding the refilling of water-conducting cells, which could involve either passive, physical processes or active, osmotic forces exerted by living cells that are associated with water-conducting cells. Several of the plant species studied are economically important crop, horticultural, and timber species, therefore insights into mechanisms of embolism repair will lead to a better understanding of drought tolerance in these plants and will have potential implications for agriculture, horticulture, and forestry, most directly for sustainable irrigation management practices. The project will continue ongoing and active involvement of undergraduate and graduate students in research, including a large number of students from underrepresented groups. The research will be done in an international collaboration with research labs in Belgium and Germany and will include international student and staff exchanges, which will expose students and researchers in all three collaborating labs to new ideas and experiences.
