The soil water deficit is the cause of negative pressure in the xylem, which can result in an abrupt change of the water meta-stable state, forming bubbles and interrupting water transport. Although embolism is well-known to occur, the xylem hydraulic properties that allow the transport of water under negative pressure and the physico-chemical properties that prevent constant embolism formation are poorly understood. One of these properties is the wettability of the xylem wall, which can nucleate or stabilize bubbles. Also, mechanisms that allow the control of hydraulic conductance under negative pressure are not completely known due to the limitations of existing methods. In fact, studies on water transport and embolism are hampered not only by the micro and nanometric scale structures involved but also several embolism artifacts due to handling a sample with water under negative pressure. Thus, in order to better understand the mechanisms that regulate water transport and enable resistance to embolism, new methods are required to minimize or even circumvent possible artifacts and to provide reliable data. We propose here the development of three different methods that will allow us (a) to estimate embolism in vivo, based on the pneumatic method originally developed for measurements of cut branches, (b) to estimate the xylem wettability based on a new hydraulic apparatus described in this project, and (c) to evaluate key factors determining the xylem hydraulic conductance, such as radial conductance and aquaporins. Based on these new methods and approaches, we will reveal the hydraulic properties of orange, coffee and eucalyptus trees, seeking a better understanding of drought resistance in these economic species.
News published in Agência FAPESP Newsletter about the scholarship: