Relating Xylem Cavitation to Transpiration in Cotton.

Acoustic emmisions (AE) from xylem cavitation events are characteristic of transpiration processes. Even though a body of work employing AE exists with a large number of species, cotton and other agronomically important crops have either not been investigated, or limited information exists. A few studies indicate that AE based irrigation control systems may be attainable, but little progress has been made. We describe preliminary greenhouse experiments characterizing the frequency of AEs from cavitation events associated with transpiration in cotton. Glasshouse grown cotton (cvar FM 958) was grown in mini-lysimeters and instrumented with LI-6400 photosynthesis systems and ultrasonic transducers interfaced with a Physical Acoustics Corporation digital signal processing unit. Whole plant transpiration, leaf level gas exchange and ultrasonic acoustic emissions were measured. Results reveal xylem cavitation events associated with increased solar loading and transpiration in the morning. AEs diminished as stomatal conductance decreased limiting transpiration rate. While we were unable to precisely quantify water loss as a function of AEs, this technique shows promise as a refinement of existing irrigation control systems based on canopy temperatures without the need for empirically determined ambient humidity control algorithms.