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2B - Natural Stressors and Toxicants (TUP/61) Dynamics and ecotoxicity of phenolic compounds in water-logged soils and sediments. Reichardt , W.1, 2, Schaffer , R.2, Lu, W.2, 3, Gamat , G.2, Angeles , O.2, 1 Marine Science Institute, UPD, Quezon City, Philippines2 International Rice Research Institute (IRRI), Los Banos, Philippines3 Zhejiang Unversity, Hangzhou, China ABSTRACT- In permanently flooded tropical rice cropping systems phenolic compounds accumulate as a function of organic input and anoxic conditions in flooded soils. Resulting increases in phenol-based ecotoxicity can severely affect biogeochemical pathways of organic matter and nutrient recycling. Sustainability of highly intensified production systems can suffer in the case of intensively cropped, tropical rice soils. Furthermore, intensified aquaculture in coastal marine environments is charging marine sediments in the tropics with increasing organic loads under predominant anoxia. While negative effects on the sustainability of this particular environment are obvious, the role of phenolic compounds has yet to be quantified. On the other hand, new insight was gained from non-marine soils and sediments. More than 3 years of soil biochemical monitoring of tropical rice soil in a long-term intensive cropping field experiment revealed strong fluctuations of soluble phenolic compounds (10-220 mg/g soil) during single cropping seasons. Furthermore there was a trend toward negative correlations between soluble phenol concentrations and activities of respiratory electron transport systems (ETS). In turn, ETS-based assays proved helpful tool in detecting adverse effects on soil biogeochemical pathways related to organic matter decomposition. Thus the diversity of microbe-mediated catabolic functions in organic matter recycling (measured by using a modified BIOLOG assay) was negatively correlated with soil phenol concentrations. Rice soils undergoing an aerated fallow period showed significantly lower phenol concentrations (mean: 52 mg/g soil) than permanently flooded soils (mean: 97 mg/g soil). Densities of phenol-degrading bacteria suggested that under anoxic conditions microbial degradation of soluble phenols can be dominated by FeIII-reducing bacteria, as long as ferric FeIII is allowed to regenerate. This regeneration is facilitated by oxygen release from the rice roots. Hence stimulation of FeIII-reducing phenol degrading bacteria by oxygen releasing roots of aquatic plants can be viewed as a promising remedy against the accumulation of soluble phenolic compounds in semi-aquatic environments serving as resource base of intensive production systems. Key words: microbiota, phenolics, flooded soils |
