Rhizosphere Iron (III) Deposition and Reduction in a Juncus effusus L.‐Dominated Wetland

Abstract

soil and rates of radial oxygen loss. Radial O 2 loss is in turn influenced by plant activity (Bedford et al., 1991; Iron (III) plaque forms on the roots of wetland plants from the Kuehn and Suberkropp, 1998) and morphological charreaction of Fe(II) with O 2 released by roots. Recent laboratory studies acteristics such as suberized and lignified roots (Armhave shown that Fe plaque is more rapidly reduced than non-rhizostrong et al., 2000). Under anaerobic conditions, the sphere Fe(III) oxides. The goals of the current study were to determine in situ rates of: (i) Fe(III) reduction of root plaque and soil Fe(III) amorphous Fe(III) oxides in root plaque serve as an exoxides, (ii) root Fe(III) deposition, and (iii) root and soil organic cellent substrate for FeRB that mediate Fe(III) reduction matter decomposition. Iron (III) reduction was investigated using a in freshwater environments (Lovley, 2000). Iron(III) novel buried-bag technique in which roots and soil were buried in reducing bacteria have been successfully enriched from heat-sealed membrane bags (Versapor 200 membrane, pore size ϭ the rhizosphere (King and Garey, 1999) where they 0.2 m) in late fall following plant senescence. Bags were retrieved can account for up to 12% of all bacterial cells (Weiss at monthly intervals for 1 yr to assess changes in total C and Fe mass, et al., 2003). Fe mineralogy, Fe(II)/Fe(III) ratio, and the abundances of Fe(II)-The juxtaposition of oxic and anoxic conditions in the oxidizing bacteria (FeOB) and Fe(III)-reducing bacteria (FeRB). The rhizosphere, separated either temporally or spatially, soil C and Fe pools did not change significantly throughout the year, results in a rhizosphere Fe cycle in which Fe plaque is but root C and total root Fe mass decreased by 40 and 70%, respectively. When total Fe losses were adjusted for changes in the ratio of alternately deposited and then reduced. Previous studies Fe(II)/Fe(III), over 95% of the Fe(III) in the plaque was reduced have reported a higher Fe(III) reduction potential in during the 12-mo study, at a peak rate of 0.6 mg Fe(III) g dry weight Ϫ1 the rhizosphere Fe(III) pool than the non-rhizosphere d Ϫ1 (gdw Ϫ1 d Ϫ1). These estimates exceed the crude estimate of Fe(III) soil pool. For example, we recently reported that Ͼ75% accumulation [0.3 mg Fe(III) g dry weight Ϫ1 d Ϫ1 ] on bare-root plants of the Fe plaque is reduced in 10 d vs. Ͻ40% of the soil that were transplanted into the wetland for a growing season. We Fe(III) oxide pool (Weiss et al., 2004). Results from anconcluded that root plaque has the potential to be reduced as rapidly other short-term (7 d) experiment examining rates of as it is deposited under field conditions. Fe(III) reduction in salt marshes support the idea of more rapid Fe(III) reduction in rhizosphere than nonrhizophere soils (Gribsholt et al., 2003). However, both radial O 2 loss and Fe(II) oxidation penetrate to some extent

Anaerobic Metabolism in Tidal Freshwater Wetlands: III. Temperature Regulation of Iron Cycling

“…Indeed, Keller et al (2012) observed near complete methanogenic conditions during peak summer months and Emerson et al (2012) found the microbial communities were dominated by methanogens, suggesting there was no significant iron reduction activity. Temperature-driven changes in the iron oxide pools are also consistent with observations from two permanently saturated non-tidal freshwater wetlands, one of which showed a sharp decrease in the iron oxide pool size beginning in May that persisted through November (Roden and Wetzel 1996), and another that showed increasing porewater [Fe(II)] during the same time frame (Weiss et al 2005).…”

“…Importantly, this temperature-driven seasonal pattern can operate independently of plant activity, providing additional mechanistic insight into seasonal shifts in the dominant carbon mineralization pathway reported by other studies (e.g., Weiss et al 2005). For example, in a study of seasonal iron cycling in saltmarsh sediments, Kostka and Luther (1995) found that [Fe(III)] was greatest during the coldest months.…”

“…Because the incubations for potential rates of iron oxidation were shaken in a fully oxic environment, we strongly suspect the dominant oxidation pathway was autocatalytic. This is not likely to be the case in circumneutral wetland soils where Fe(II)-oxidizing bacteria are abundant (Emerson et al 1999;Weiss et al 2003Weiss et al , 2005. We do not have a reason to suspect that the temperature Fig.…”

Review on iron availability in soil: interaction of Fe minerals, plants, and microbes

“…Due to the fast rate of this spontaneous reaction, the activity of neutrophilic bacteria has generally been considered very slow (Sobolev and Roden 2004). Recently, the presence of Fe III precipitates associated with the activity of many neutrophilic bacteria (Gallionella and Leptothrix species) observed in a variety of soil and water environments suggests that microbial Fe II oxidation can successfully compete with Fe II abiotic oxidation (Weiss et al 2004(Weiss et al , 2005Duckworth et al 2009). …”

The impact of sea-level rise on organic matter decay rates in Chesapeake Bay brackish tidal marshes

“…Here we consider the effect of elevation and hydroperiod on the decomposition rate of soil organic matter (SOM) using the method of Weiss et al (2005). SOMbags were constructed from a non-reactive synthetic membrane (Versapor © ; Pall Corporation, Port Washington, NY) with a 5 µm pore size to allow adequate flow of water and access to microbes, but to restrict the passage of soil particles.…”