title: Field measurements of ultrasonic acoustic emissions and stem diameter variations. New insight into the relationship between xylem tensions and embolism.
abstract: We examined interrelated xylem water tensions and embolism dynamics under field conditions by simultaneously monitoring ultra-acoustic emissions and changes in stem xylem diameter. Variation in stem xylem diameter was measured with linear displacement transducers to estimate variation in sap tension. Measured ultrasonic acoustic emissions coincided well with changes in xylem diameter, indicating that individual peaks in embolism occurred simultaneously with peaks in water tension. The good time resolution between measurements makes this method especially suitable for observing embolism dynamics on a short timescale. Longer lasting measurements can also be made to monitor inter-daily patterns in water tension and embolism because the techniques are non-destructive. Ultra-acoustic emissions occurred mainly during periods of decreasing stem xylem diameter, i.e., increasing water tension, when the water tension was high enough. Embolism also occurred during periods of increasing xylem diameter, i.e., decreasing water tension, but the number of embolizing conduits under these conditions was small.
authors.affiliation: Department of Physical Sciences, PO Box 64, FIN-00014 University of Helsinki, Finland. teemu.holtta@helsinki.fi
authors.forename: T
authors.initials: T
authors.lastname: Hölttä
authors.forename: T
authors.initials: T
authors.lastname: Vesala
authors.forename: E
authors.initials: E
authors.lastname: Nikinmaa
authors.forename: M
authors.initials: M
authors.lastname: Perämäki
authors.forename: E
authors.initials: E
authors.lastname: Siivola
authors.forename: M
authors.initials: M
authors.lastname: Mencuccini
mesh_terms: D041605:Pinus sylvestris / Q000502:physiology*; D018547:Plant Stems / Q000502:physiology; D018526:Plant Transpiration / Q000502:physiology; D014197:Trees / Q000502:physiology*; D014465:Ultrasonics; D052584:Xylem / Q000033:anatomy & histology / Q000502:physiology*