David L. Jones, Abdul M. Prabowo, Leon V. Kochian
The kinetics and characteristics of malate degradation were studied in four acid soils ranging in both pH (4.30 to 5.00) and vegetation type. The breakdown of malate was rapid in all soils with a half life of approximately 1.7 h, K(m) of 1.7 mM and V(max) of 70 nmol g-1 soil h-1. No relationship was observed between malate decomposition rate and pH. Co-metabolism studies with other C and N substrates (glucose, glycine, glutamate, citrate and succinate) indicated that the microorganisms were not N limited and competitive inhibition of malate breakdown was only observed in the presence of succinate. Studies with isolated mixed bacterial cultures indicated that the bacterial malate uptake was mediated by an energy dependent, dicarboxylate transporter which can be inhibited by succinate and is independent of pH between pH 5.0 and 7.0. The K(m) and V(max) parameters ranged from 279-955 μM and 0.1-17 μmol mg-1 protein h-1 for the mixed bacterial cultures depending on the bacteria's previous C source. The results indicate that in acid topsoils where microbial populations are high, the microbes may provide a considerable sink for organic acids. If organic acids are being released by roots in response to an environmental stress (e.g. Al toxicity, P deficiency) it can be expected that the efficiency of these root mediated metal resistance mechanisms will be markedly reduced by rapid microbial degradation.
School of Agricultural and Forest Sciences, University of Wales, Bangor, Gwynedd LL57 2UW, United Kingdom; Department of Soil Science, Brawijaya University, Malang, Indonesia; U.S. Plant Soil and Nutrition Laboratory, USDA-ARS, Cornell University, Ithaca, NY 14853, United States
