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|Title:||Effect of Microbial Exopolysaccharides in Soil on Metal Availability to Plants (Copper, Cadmium, Binding)|
|Author(s):||Miller, Kathleen Wilber|
|Department / Program:||Agronomy|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Abstract:||Many microorganisms in soil produce extracellular polysaccharides. Often these materials are anionic due to acidic subunits and substituents. As such, they are potential binding sites for metallic cations--some that are necessary for plant nutrition, and others that are pollutant metals of anthropogenic origin. This research sought the answers to three questions: (1) What is the affinity and capacity of exopolysaccharides for bound metals? (2) Do exopolysaccharides persist in soils long enough for their metal binding to affect the concentration of metals in the soil solution? (3) Can exopolysaccharides diminish metal uptake by plants?
Exopolysaccharides from Arthrobacter viscosus NRRL B-1797, A. viscosus NRRL B-1973, Lipomyces starkeyii NRRL Y-1389, and Hansenula capsulata NRRL Y-1842 were subjected to Cu and Cd binding studies. For Cu, in 0.001 M KClO(,4), log of the conditional stability constants, as determined by Scatchard plots, ranged from 3.9 to 5.7; capacity ranged from 409 to 698 (mu)mol/g. Values in 0.01 M KClO(,4) were lower. Similar results were obtained with Cd.
Degradation of radiolabelled exopolysaccharides in a fine sand soil occurred rapidly, with up to 60% being evolved as CO(,2) after 1 wk. Degradation appeared to be slower in a silty clay loam; after 8 wk, 12% at most was evolved. Bound Cu did not decrease the rates of degradation in either soil.
Cd, free in solution, and Cd-exopolysaccharide mixtures were introduced into a fine sand soil planted with corn seedlings. Exopolysaccharides afforded the seedlings some protection against the phytotoxic effects of Cd. However, uptake of Cd was enhanced, rather than diminished, in the presence of exopolysaccharides.
The results suggest that microbial activity in the form of exopolysaccharide production can decrease the concentration of free metals in the soil solution. However, the transitory nature of exopolysaccharides in soils prevents their becoming long-term repositories for metals.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1985.
|Date Available in IDEALS:||2014-12-16|