Iron Oxidation at the Surfaces of Slash Pine Roots from Saturated Soils

Abstract

Abstract Root aeration in saturated gleyed soils is indicated by Fe oxide coatings on live‐root surfaces. Oxygen diffusing through gas‐permeable tissues, from the atmosphere to submerged roots, ultimately diffuses into and oxidizes the rhizosphere. The objectives of this study were to: (i) characterize the oxidizing conditions of slash pine ( Pinus elliottii Engelm. var. elliottii ) roots growing in saturated conditions, and (ii) test the hypothesis that submerged taproot systems are internally aerated. One study examined Fe‐oxide deposits on the roots of six saplings grown outdoors in drums filled with saturated, Fe‐amended peat. Another study examined roots of two mature slash pines growing naturally on a poorly drained Paleaquult. Orange Fe‐oxide precipitates coasted cortical tissue of sapling taproots and root branches growing in saturated peat. Iron concentrations in these roots were 6 to 96 times greater than in the surrounding peat. In gleyed horizons of the Paleaquult, Fe‐rich precipitates cemented sand to the surfaces of large‐diameter roots and entirely ensheathed fine roots of pine and pine cypress ( Taxodium ascendens Brogn.). Prominent mottles, all neoferrans, surrounded fine pores, remnants of decayed‐root channels. Despite the anoxic growing conditions, all of the examined slash pine root systems oxidized and accumulated Fe, supporting other evidence that the taproot systems of slash pine growing in wet soils are internally aerated.