Rhizosphere pH along different root zones of Douglas-fir (Pseudotsuga menziesii), as affected by source of nitrogen

Abstract

Douglas-fir, grown on strongly acid soil (pH-H20 3.87), was fertilized with ammonium, nitrate or ammonium nitrate as N-source. Rhizosphere pH along the root axis was measured with microelectrodes. Pure ammonium supply resulted in acidification of the rhizosphere, almost along the entire root axis; only the extreme root tip was slightly alkaline compared with the bulk soil. With nitrate supply, the alkalization of the rhizosphere at the root tip was considerably stronger than with ammonium supply and the length of the alkalization zone greater, extending over the entire growth zone of the root. Acidification of the rhizosphere along the older parts of the root was less pronounced in the case of nitrate. It is concluded that nitrate nutrition enables the plant to protect its most essential root zone from the adverse effects of strong acidity by locally raising the rhizosphere pH.

Vegetable cultivation under greenhouse conditions leads to rapid accumulation of nutrients, acidification and salinity of soils and groundwater contamination in South-Eastern China

“…2a and 3a). Nitrate uptake and assimilation by root cells can significantly increase soil pH (Gijsman 1990;Marschner et al 1991). On the other hand, the rainfall during the period from June to September 2005 reached a high level of 550 mm (Fig.…”

“…4a). Soil pH increase can be caused by a number of factors such as ammonification of urea (Watson et al 1990) or application of alkaline fertilizers such as ammonium-bicarbonate, nitrate uptake and assimilation by plants (Gijsman 1990;Marschner et al 1991), denitrification by soil microorganisms under reduced conditions (Li et al 2003), decarboxylation of organic anions applied with manure or plant residues (Yan et al 1996;Yan and Schubert 2000). On the other hand, soil pH decrease can be caused by numerous processes such as nitrification, oxidation of organic sulfur, oxidation of iron or manganese and anaerobic decomposition of organic substance, etc.…”

Diurnal cycles of rhizosphere acidification byPinus contorta seedlings

“…and Psudotsuga menziesii (Mirb.) Franco (Gijsman, 1990a;H~ussling et al, 1985;Marschner et al, 1985cited in Gijsman, 1990a. Thus the rate we observed for P. contorta was high, but not unreasonably so if proton pumps along most of the length of the roots were activated by ammonium exposure.…”

Empirical evidence of a convection–diffusion model for pH patterns in the rhizospheres of root tips

“…Classical plant nutrition emphasizes the importance of root-induced changes in rhizosphere pH. Working to decrease rhizosphere pH can be high-ammonium relative to nitrate concentration (Arnon 1937;Riley & Barber 1971;Gijsman 1990;Raven 1988;Miller et al 1991;Henriksen et al 1992;Taylor & Bloom 1998), the presence of nitrogenfixing nodules in leguminous species (e.g. Hauter & Mengel 1988) and the secretion of organic acids by proteoid roots (e.g.…”