PARENT SESSION
Contributed Oral Session 16: Photosynthesis and Water Relations: Conductivity; Stress
Monday, August 8, 8:00 AM - 11:30 AM, Meeting Room 524 A, Level 5, Palais des congrès de Montréal
Diurnal pattern in water tension of tree stems begins before bud break and does not cease with leaf fall.
Sevanto, Sanna*,1, Holbrook, N. Michele1, Zwieniecki, Maciej1, Mikkelsen, Teis2, Munger, J. William3, Wofsy, Steven3, 1 Department of Organismic and Evolutionary Biology, Cambridge, MA, USA2 Plant Research Department, Roskilde, Denmark3 Department of Earth and Planetary Sciences, Cambridge, MA, USA
ABSTRACT- Tree stem diameter varies diurnally because of transpiration-induced tension in the sap. The diameter is largest just before sunrise in the morning and smallest in early afternoon when transpiration rates are highest. Xylem diameter variations are exceedingly closely linked with transpiration. Even the small variations in transpiration rate (and thus water tension) resulting from (e.g.) changes in cloud cover are observable in xylem diameter. Including bark tissue in the measurements results in a pattern similar to xylem diameter variations, but the small variations become smoothed and the amplitude increases. The dynamics between xylem and over-bark diameter variations has been suggested to be linked with sap flow patterns in the phloem and xylem-phloem interactions. We have measured stem diameter variations on and below bark during the bud break and leaf fall periods of deciduous trees. Interestingly we observed that the diurnal pattern started before leaves were open and did not completely cease straight after leaf fall. This result suggests that some other mechanism than transpiration drives water circulation at these times. In this presentation possible explanations are discussed.
Key words: sap flow, stem diameter variation, transpiration