. Auxins and plant growth. Auxin; Plant growth promoting substances. Application and Persistence 199 Destruction. The third major factor in persistence of auxins in soils is the destruction of the auxin by microorganisms. The earliest workers on auxin persistence in soils concluded that the destruction was due to microorganism activity, for autoclaving prevented destruc- tion, and moisture and temperature conditions suitable for micro- organism growth were found to be necessary for auxin destruction (DeRose and Newman, 1947; Brown and Mitchell, 1948). An ingenious extension of this point has b
. Auxins and plant growth. Auxin; Plant growth promoting substances. Application and Persistence 199 Destruction. The third major factor in persistence of auxins in soils is the destruction of the auxin by microorganisms. The earliest workers on auxin persistence in soils concluded that the destruction was due to microorganism activity, for autoclaving prevented destruc- tion, and moisture and temperature conditions suitable for micro- organism growth were found to be necessary for auxin destruction (DeRose and Newman, 1947; Brown and Mitchell, 1948). An ingenious extension of this point has been made by Audus (1951) who found that respiratory poisons were likewise effective in preventing destruc- tion. This same worker (1950) isolated the first microorganism which was found to be capable of destroying 2,4-D, and it turned out to be a gram negative bacterium of the Bacterium globiforme type. Subse- quently Jensen and Peterson (1952) have isolated another micro- organism capable of destroying 2,4-D, Flavobacterium aquatile. The time course in the destruction of some auxins in the soil is shown in figure 83. Audus (1949, 1951) has shown that the rate of destruction varies greatly with the auxin used, 2,4-D being the most rapidly destroyed auxin which was tested and 2,4,5-T being the most persistent. Audus sometimes observed a small, immediate initial loss of auxin activity. He suggested that such an initial loss may be a result of adsorption of the auxin by the soil. The slow rates of micro- bial destruction in the early sections of each of the curves in figure ^ 20- 0) o UJ o z UJ I- (^ (/) tt: UJ CL. 10 20 CONC. OF 50 MG/L AUXIN Fig. 84. The effect of various concentrations of auxin (2,4-D) upon the time of persistence of the auxin in the soil (Newman and Thomas, 1949).. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemb
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