Internal oxygen transport in cuttings from flood-adapted varzea tree species

Abstract

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.

The effect of flooding on the exchange of the volatile C<sub>2</sub>-compounds ethanol, acetaldehyde and acetic acid between leaves of Amazonian floodplain tree species and the atmosphere

“…alanine, malate and succinate, as reported for other tropical tree species (De Simone, 2002;Joly, 1991;Schlüter et al, 1993). In the case of T. juruana, the flooding induced proliferation of hypertrophied lenticels at the stem, which can serve as an inlet for oxygen and enhance root aeration (Haase et al, 2003), could have contributed to a reduced ethanol production. Simultaneous release of ethanol could have occurred through this route and may have been overlooked because the lower part of the stem was not enclosed by the cuvette.…”

Molecular and physiological responses of trees to waterlogging stress

“…Adventitious roots possess a high portion of intercellular spaces facilitating longitudinal oxygen transport. In a studies with Central Amazonian trees, such as Salix martiana and Tabernaemontana juruana, it was demonstrated that the main entry point of atmospheric oxygen were gas-permeable pores in the stem near the origin of the adventitious roots (Haase et al 2003;Haase & Rätsch 2010). Uptake of oxygen seems also to be possible along the root if it is growing at the water surface being in contact with the atmosphere (Haase et al 2003).…”

“…Uptake of oxygen seems also to be possible along the root if it is growing at the water surface being in contact with the atmosphere (Haase et al . ). Such oxygen uptake is required for the maintenance of mitochondrial respiration; it further allows radial oxygen loss (ROL) from the roots which contributes to the oxidation of the rhizosphere (Kludze et al .…”

Estimation of symbiotic N2 fixation in an Amazon floodplain forest

“…Different adaptations of Va´rzea plants to periodical flooding have been studied. Pressurised or diffusive gas transport are strategies supporting a sufficient O 2 supply for the root system (Haase et al 2003), and may also maintain symbiotic N 2 fixation during flooding. Symbiotic N 2 fixation during the aquatic phase in the Va´rzea was reported before, during mid-rising water of the Amazon River and high water of the Madeira River (Martinelli et al 1992).…”