Ht. Gollany et Te. Schumacher, COMBINED USE OF COLORIMETRIC AND MICROELECTRODE METHODS FOR EVALUATING RHIZOSPHERE PH, Plant and soil, 154(2), 1993, pp. 151-159
Plant control of rhizosphere pH is important for nutrient mobilization
and uptake, and also affects microbial activity and pathogens in the
vicinity of the root. Limited information is available on the ability
of plant species and genotypes within a species to induce pH changes i
n the rhizosphere. A growth chamber study was conducted to characteriz
e patterns of pH change within the rhizosphere of selected genotypes i
n an alkaline environment with a balanced nutrient supply. After germi
nation in incubators, seedlings of 32 genotypes of maize (Zea mays L.)
, soybean (Glycine max. L.), sorghum (Sorghum bicolor L.), sordan [sor
ghum (Sorghum bicolor L.), sudangrass (Sorghum sudanese L.) hybrid], w
heat (Triticum aestivum L.), oats (Avena sativa L.), and barley (Horde
um vulgare L.) were transferred into aseptic agar medium (pH 7.6) with
bromocresol purple indicator. Ability of the embedded roots to induce
rhizosphere pH change was followed by photographing the color change
of the bromocresol purple indicator. The pH for selected genotypes at
different root zones (maturation, elongation, meristematic) was also m
onitored by a microelectrode at l-, 2-, 3- and 4-mm distances from the
root surface. Rhizosphere acidification for selected genotypes within
a species were in the order: soybean, Hawkeye > PI-54169; maize, Pion
eer-3737 > Pioneer-3732 > CM-37; sordan, S-757 > S-333; sorghum, SC-33
-8-9EY congruent-to SC-1 18-15E; barley, Bowman > Primus 11; oats, Hyt
est > SD-84104. The pH patterns within the root system varied from spe
cies to species. The highest amount of acidification was found at the
elongation and meristematic zones for soybean, while the highest amoun
t of acidification was found at the maturation zone for barley under t
he same experimental conditions. The agar method allowed the determina
tion of a genotype's capability to induce rhizosphere pH changes while
the microelectrode method is necessary for quantifying the spatial va
riation of specific root developmental zones with high resolution.