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Braun, Martin ; Dieffenbach, Antje ; Matzner, Egbert:
Soil solution chemistry in the rhizosphere of beech (Fagus silvatica L.) roots as influenced by ammonium supply.
In: Journal of Plant Nutrition and Soil Science.
Bd. 164
(2001)
Heft 3
.
- S. 271-277.
ISSN 1436-8730
DOI: https://doi.org/10.1002/1522-2624(200106)164:3<271::AID-JPLN271>3.0.CO;2-G
Abstract
Roots can induce significant changes in the rhizosphere soil. The aim of the present study was to investigate the influence of beech (Fagus silvatica L.) roots on the chemistry of the rhizosphere soil solution. Special emphasis was given to the effect of the NH4+ supply since many forest soils presently receive high NH4+ inputs from atmospheric deposition. In a mature beech stand, a non-mycorrhized long root was forced to grow into a rhizotrone filled with homogenized acidic forest soil from the Bw horizon of a Dystric Cambisol. Beside the control, a NH4+ enriched treatment was installed. Thirty micro suction cups of 1 mm diameter and 0.5 cm length were placed in a systematic grid of 5 × 10 mm in each rhizotrone to enable root growth through the grid. The water potential of the soil was kept constant by supplying a synthetic soil solution. Small amounts of soil solution were sampled periodically from May to October 1999 and analyzed by capillary electrophoresis for major cations and anions. Furthermore, pH and conductivity were measured by micro electrodes. In the laboratory experiments, beech seedlings were grown in rhizotrones in a control and in a NH4+ fertilized soil. The equipment for sampling soil solutions and the soil conditions in the laboratory was similar to the field experiment. In each rhizotrone a single long root grew through the lysimeter grid. The laboratory conditions induced higher rates of nitrification as compared to the field. Thus, the overall concentration range of the soil solution was not comparable between field and laboratory studies. In all treatments average soil solution concentrations of H+ and Al3+ were significantly higher in the rhizosphere than in the bulk soil. The NH4+ treatment resulted, in the field and laboratory, in a strong increase of the H+ and Al3+ concentrations in the rhizosphere, accompanied by an accumulation of Ca2+, Mg2+, and NO3—. The observed rhizosphere gradients in soil solution chemistry were highly dynamic in time. The results demonstrate that the activity of growing beech roots results in an acidification of the soil solution in the rhizosphere. The acidification was enhanced after the addition of NH4+.