Renate Wendler

Downward migration of radiocaesium in organic soils across a transect in Scotland.

Following the accident at the Chernobyl nuclear power plant in 1986, radioactive materials including (137)Cs were distributed over large parts of the former Soviet Union and Europe. Due to the relatively long physical half-life of (137)Cs (30.1 y) measurable activity concentrations can still be observed in the natural environment. We have determined the depth distribution of (137)Cs from the testing of nuclear weapons in the atmosphere and Chernobyl, in eight highly-organic soils along an approximately east to west transect across the Central Highlands of Scotland. The (137)Cs activity concentrations in the soil profiles, corrected for radioactive decay to May 1986, were between 2.8 and 14.4 kBq m(-2). There were differences in the pattern of distribution of (137)Cs in the soil profiles. The mean migration depth of (137)Cs in the soil profiles was 12.2 cm with a range between 8.2 and 17.4 cm. Quantitative mineralogical analysis of the ash obtained after heating the soil to 400 °C indicated that clay minerals alone did not have a prime role in controlling the migration of (137)Cs down the profile.

Phosphorus acquisition by citrate- and phytase-exuding Nicotiana tabacum plant mixtures depends on soil phosphorus availability and root intermingling

Citrate and phytase root exudates contribute to improved phosphorus (P) acquisition efficiency in Nicotiana tabacum (tobacco) when both exudates are produced in a P deficient soil. To test the importance of root intermingling in the interaction of citrate and phytase exudates, Nicotiana tabacum plant-lines with constitutive expression of heterologous citrate (Cit) or fungal phytase (Phy) exudation traits were grown under two root treatments (roots separated or intermingled) and in two soils with contrasting soil P availability. Complementarity of plant mixtures varying in citrate efflux rate and mobility of the expressed phytase in soil was determined based on plant biomass and P accumulation. Soil P composition was evaluated using solution 31 P NMR spectroscopy. In the soil with limited available P, positive complementarity occurred in Cit+Phy mixtures with roots intermingled. Root separation eliminated positive interactions in mixtures expressing the less mobile phytase (Aspergillus niger PhyA) whereas positive complementarity persisted in mixtures that expressed the more mobile phytase (Peniophora lycii PhyA). Soils from Cit+Phy mixtures contained less inorganic P and more organic P compared to monocultures. Exudate-specific strategies for the acquisition of soil P were most effective in P-limited soil and depended on citrate efflux rate and the relative mobility of the expressed phytase in soil. Plant growth and soil P utilization in plant systems with complementary exudation strategies are expected to be greatest where exudates persist in soil and are expressed synchronously in space and time.