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(491) Effect of cultivation conditions on organic acid exudation and weathered p,p'-DDE phytoextraction by plants.
White, J.1, Wang, X.1, Incorvia Mattina, M.1, Gent, M.1, 1 Connecticut Agricultural Experiment Station, New Haven, CT, 06504
ABSTRACT- Previous field studies from our laboratory indicate that zucchini and cucumber are good and poor accumulators, respectively, of persistent organic pollutants from soil. We hypothesize that exuded organic acids facilitate the uptake of persistent organic pollutants by increasing contaminant bioavailability to plants. This study compared DDE uptake, organic acid exudation, and soil structure disruption by zucchini and cucumber under 3 cultivation regimes; field planting, non-dense planting in pots (1 plant, 80 kg soil), and dense planting in pots (5 plants, 5 kg soil). Under field conditions, the uptake and translocation of DDE by zucchini and cucumber, as well as the rhizosphere concentrations of organic acids and water extractable soil elements, were as expected for uptaker and nonuptaker species. Similarly, under dense planting, zucchini accumulated significant and expected amounts of DDE with a BCF (bioconcentration factor, DDE concentration in plant tissue relative to that in soil) of 10 for roots and 2.5 for stems. Surprisingly, under these stressed conditions, cucumber accumulated similar amounts of DDE in the roots with a BCF of 12, but translocation to aboveground tissues was negligible. The concentrations of citric, malic, formic and acetic acids in the rhizosphere soil of cucumber under dense planting were significantly higher than zucchini, suggesting that the unexpected DDE uptake by cucumber was due to increased organic acid exudation under nutrient stressed conditions. Under dense planting conditions, cucumber developed an extensive fibrous root system not observed under field conditions. In non-dense planting, both fine and thick roots from a single plant could be analyzed for DDE content. The DDE concentration in zucchini and cucumber fine roots was 2.9 and 5.3 times greater than the concentration in the thick roots, respectively. The role of cultivation conditions and nutrient availability in controlling root morphology, organic acid exudation, and contaminant uptake will be discussed.
Key words: organic acid exudation, phytoremediation, POPs, bioavailability
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