© 2003 Heron Publishing—Victoria, Canada
Internal oxygen transport in cuttings from flood-adapted várzea tree species
Karen Haase (1), Oliviero De Simone (1), Wolfgang J. Junk (1) and Wolfgang Schmidt (2, 3, 4)
1. Max-Planck Institute for Limnology, Tropical Ecology Workgroup, P.O. Box 165, D-24302 Plön, Germany / 2. University of Oldenburg, Department of Biology, P.O. Box 2503, D-26111 Oldenburg, Germany / 3. Humboldt University Berlin, Invalidenstraße 42, 10115 Berlin, Germany / 4. Author to whom correspondence should be addressed (wolfgang.schmidt@botany.de) / Received November 21, 2002; accepted April 5, 2003; published online September 15, 2003
Summary
Tree species from the Central Amazon inundation areas are subjected to extreme flooding, with trees being partially submerged
for up to 10 months. The rapidly advancing floodwater table at the onset of the aquatic phase interrupts the inward diffusion
of oxygen from the atmosphere to submerged plant parts. Salix martiana (Leyb.) (Salicaceae) and Tabernaemontana juruana ((Markgr.) Schumann ex J. F. Macbride) (Apocynaceae), tree species typical of Amazon floodplains, respond to low oxygen concentrations
by forming adventitious roots capable of longitudinal oxygen transport. Cuttings of these tree species were subjected to simulated
flooding and the oxygen concentration of the root cortex was temporally monitored by oxygen microelectrodes that penetrated
the roots. Changes in the floodwater table made it possible to localize precisely the entry points of atmospheric oxygen.
Under experimental conditions, mathematical description of the transport kinetics revealed that longitudinal transport of
O2 in both species was mainly attributable to diffusion. Based on the finding that diffusion was inhibited by a small increase
in the floodwater table, we conclude that internal oxygen transport during a rising water table is only attainable when adventitious
roots are continuously and rapidly developed, as is the case in S. martiana. In T. juruana, slow growth of adventitious roots and low root porosity suggest that other adaptations are required to overcome long flooding
periods.
Keywords:
aerenchyma, flooding, lenticels, radial oxygen loss, root porosity, suberization, várzea.
