HR: 1340h
AN: B43A-0257    [Abstracts]
TI: Mineral Dissolution and Metal Mobility From Rhizosphere and Non-rhizosphere Soils by Low Molecular Weight Organic Acids
AU: * Little, D A
EM: David.Little@csiro.au
AF: CRC LEME, School of Resources, Environment and Society, Australian National University, Canberra, ACT 0200 Australia
AU: Field, J B
EM: john.field@anu.edu.au
AF: CRC LEME, School of Resources, Environment and Society, Australian National University, Canberra, ACT 0200 Australia
AU: Welch, S A
EM: swelch@ems.anu.edu.au
AF: CRC LEME Department of Earth and Marine Sciences, Australian National University, Canberra, ACT 0200 Australia
AB: This research is part of an ongoing investigation of micro-biogeochemistry in the rhizosphere of co-occurring Eucalyptus mannifera and Acacia falciformis on the Southern Tablelands of New South Wales, Australia. While there is still considerable controversy in the literature regarding the roles of low molecular weight organic acids in soil processes there is growing evidence suggesting low molecular weight compounds, especially di-carboxylic acids, have large impacts on mineral dissolution and metal mobility in the rhizosphere. Rhizosphere and non-rhizosphere samples from adjacent E. mannifera and A. falciformis trees were subjected to four separate treatments in sets of 3 replicates; +oxalic acid, +malic acid, +citric acid or +NaCl control solution. These three acids were chosen because they are produced by rhizosphere species and they form stable complexes with nutrient elements such as Phosphorus (P), Iron (Fe), and Calcium (Ca). Solution samples were collected at day 1, day 8 and day 15 for pH measurement and analysed for major and trace elements by ICP-AES and ICP-MS. The results of the preliminary dissolution experiments show that milli-molar concentrations of individual organic acids, malate and oxalate, and in particular citrate, greatly increase the release of major and trace metals to solution compared to inorganic controls. Concentrations of Al and Fe in organic acid solutions were up to 10 times greater than in the inorganic controls. Si concentrations were a factor of 2-5 greater in the organic acid solutions, suggesting preferential weathering of Fe and Al oxyhydroxide phases rather than primary silicate minerals. Dissolution of elements such as Si, Al and Fe from rhizosphere soils were about twice that observed from non-rhizosphere soils, further supporting this. Interestingly Ti and Zr, which are usually considered to be immobile during chemical weathering and are not usually taken up by plants, were also mobilised from the rhizosphere soils, especially in the citric acid solution.
DE: 0409 Bioavailability: chemical speciation and complexation
DE: 0412 Biogeochemical kinetics and reaction modeling (0414, 0793, 1615, 4805, 4912)
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0463 Microbe/mineral interactions
DE: 0470 Nutrients and nutrient cycling (4845, 4850)
SC: Biogeosciences [B]
MN: Fall Meeting 2005