Department of Plant Sciences

Root-induced pH changes in the rhizosphere significantly modified the root environment and the mobility of mineral. With an image scanner and image analysis of agar gel containing a pH indicator, three plant species [Cowpea (Vigna unguiculate L. Walp. cv), soybean (Glycine max L.), and sunflower [(Helianthms annuus L.)] were examined in terms of the localization of root-induced pH changes along a single root in different treatments under light conditions. In the three plant species exposed to Al3+ the phenomenon of rhizosphere acidification was the same as in the treatment with only potassium nitrate. The localized occurrence of acidification was in the middle portion of the root axis and was regulated by photosynthetic activity. The release of protons may be caused by relatively higher uptake of cations in light. The addition of Al3+ stress may not trigger the release of organic anions from the roots. Organic acid exudation probably is not one of the factors which cause rhizosphere acidification in this study. On the other hand, according to our experiments it is concluded that the uptake of cations coupled with the process associated with root respiration could be one of the factors causing the acidification in three plant species.Therefore, compared with the corresponding excretion of protons under the exposure of shoot to light, the contribution to rhizosphere acidification might be related to photosynthetic activity and proton pump of plasmalemma and CO2 release from root respiration.