Rhizosphere pH Changes Induced by Exposure of Shoot to Light.

Rhizosphere pH is known to be strongly influenced by nitrogen sources and plant species. We have evaluated whether the exposure of the shoot to light affects the pH changes in the rhizosphere of legumes and cereals in the presence of different forms of nitrogen (ammonium, nitrate or both). The pH changes in the rhizosphere were quantified as apparent proton fluxes by image analysis of agar gel containing a pH indicator, in which the root was embedded. In the presence of ammonium or ammonium nitrate, the rhizosphere was alkalized under dark conditions and acidified under light conditions in both cowpea and sorghum. This implied that, in the presence of ammonium, acidification of the rhizosphere is induced by exposure of shoot to light. In the presence of nitrate, both plants alkalized their rhizospheres in the dark, whereas in the light cowpea acidified its rhizosphere although sorghum alkalized it. Light-induced acidification in the presence of nitrate, was also found in chickpea and adzuki bean, but not in maize. We found, that a particular part of the root axis strongly acidifies the rhizosphere in response to the exposure of shoot to light, especially in legumes. We conclude that rhizosphere pH is strongly affected by the light conditions encountered by the shoot, and the pH changes in response to the light locally along the root axis.

[1]  K. Yano,et al.  A Simple Method for Quantitative Estimation of Rhizosphere pH along Root Axes through Visualization , 2000 .

[2]  Philippe Hinsinger,et al.  How Do Plant Roots Acquire Mineral Nutrients? Chemical Processes Involved in the Rhizosphere , 1998 .

[3]  M. Dhanoa,et al.  An analysis of the physiological basis of commonality between diurnal patterns of NH4+, NO3- and K+ uptake by Phleum pratense and Festuca pratensis , 1997 .

[4]  P. Hinsinger,et al.  Mobilizationof Phosphate from Phophate Rock and Alumina-Sorged phosphate by the roots of Ryegrass and Clover as related to Rhizosphere PH , 1996 .

[5]  A. Ourry,et al.  Diurnal variation in the simultaneous uptake and ‘sink’ allocation of NH4+ and NO3- by Lolium perenne in flowing solution culture , 1996 .

[6]  Byoung Ryong Jeong,et al.  Influence of ammonium, nitrate, and chloride on solution pH and ion uptake by ageratum and salvia in hydroponic culture , 1996 .

[7]  P. Tillard,et al.  Diurnal regulation of NO3− uptake in soybean plants I. Changes in NO3− influx, efflux, and N utilization in the plant during the day/night cycle , 1995 .

[8]  E. Delhaize,et al.  Aluminum Toxicity and Tolerance in Plants , 1995, Plant physiology.

[9]  E. A. Kirkby,et al.  Diurnal uptake of nitrate and potassium during the vegetative growth of tomato plants , 1992 .

[10]  E. A. Kirkby,et al.  Influence of Nitrate and Ammonium Nutrition on the Uptake, Assimilation, and Distribution of Nutrients in Ricinus communis. , 1988, Plant physiology.

[11]  W. G. Keltjens,et al.  Diurnal variations in uptake, transport and assimilation of NO3 ‐and efflux of OH‐ in maize plants , 1987 .

[12]  H. Marschner.  Mineral Nutrition of Higher Plants , 1988 .

[13]  Walter J. Horst,et al.  Root-induced changes in the rhizosphere: Importance for the mineral nutrition of plants , 1986 .

[14]  S. Jarvis,et al.  Rates of hydrogen ion efflux by nodulated legumes grown in flowing solution culture with continuous pH monitoring and adjustment , 1985 .

[15]  V. Römheld,et al.  An Improved Method for Non-destructive Measurements of the pH at the Root-Soil Interface (Rhizosphere). , 1985, Journal of plant physiology.

[16]  V. Römheld,et al.  In vivo Measurement of Root-induced pH Changes at the Soil-Root Interface: Effect of Plant Species and Nitrogen Source , 1983 .

[17]  D. Barber,et al.  The acquisition of phosphorus by Lupinus albus L., 2: the effect of varying phosphorus supply and soil type on some characteristics of the soil/root interface , 1982 .

[18]  L. Jaffe,et al.  Natural H Currents Traverse Growing Roots and Root Hairs of Barley (Hordeum vulgare L.). , 1979, Plant physiology.

[19]  S. A. Barber,et al.  Effect of Ammonium and Nitrate Fertilization on Phosphorus Uptake as Related to Root-Induced pH Changes at the Root-Soil Interface 1 , 1971 .