PARENT SESSION
Oral Session # 8: Plant Ecology I: Physiology and Function I.
Presiding: E Hamerlynck
Monday, August 4. 8:00 AM to 11:30 AM, SITCC Meeting Room 200.
How are leaves plumbed on a shoot? A novel hydraulic approach to quantifying species-specific sectoriality.
Orians, Colin *,1, 2, Smith, Sigrid1, Sack, Lawren2, 1 Tufts University, Medford, MA2 Harvard University, Cambridge, MA
ABSTRACT- Most vascular plants exhibit "sectoriality" -- the restricted movement of water, nutrients, photosynthate, chemical signals, and other substances along specific vascular pathways, known as Integrated Physiological Units (IPUs). From qualitative dye studies we found that leaves on a shoot are arranged in discrete sectors. However there is variation among species in sectoriality. We employed a novel hydraulic technique to quantify patterns of sectoriality in current year shoots of 1-2 species of Acer, Betula, Castanea, Fraxinus, Liriodendron and Quercus with at least six fully expanded leaves. We measured the hydraulic resistance of the pathways between leaves on the shoot. We severed each shoot under solution (10mM KCl), and excised the terminal apex and 6-8 successive leaves, leaving only 2 cm petiole stubs. The base and tip of each shoot were sealed with acrylic-based glue, and petiole stubs were attached to tubes filled with KCl solution. KCl solution was applied to one petiole stub at a known pressure, and flow was measured out of the other petiole stubs, and hydraulic resistance was quantified as the applied pressure divided by the flow rate (normalized by leaf area). As expected, resistance of flow between leaves within an IPU was low in all species. Resistance to flow between IPUs varied among species, indicating variation in shoot sectoriality. Resistance between IPUs was significantly higher relative to resistance within IPUs for ring-porous species (Castanea, Fraxinus and Quercus), indicating greater sectoriality than for diffuse-porous species (Acer, Betula and Liriodendron). In Betula resistance between IPUs was the same as resistance within IPUs. Species-differences in internal plumbing have potential implications for the coordination of long-distance transport, as well as for responses to heterogeneity in resource supply and herbivory.
Key words: ring-porous vs. diffuse-porous, trees, vascular architecture, hydraulics