Root induced changes of effective 1D hydraulic properties in a soil column

AIMS

Roots are essential drivers of soil structure and pore formation. This study aimed at quantifying root induced changes of the pore size distribution (PSD). The focus was on the extent of clogging vs. formation of pores during active root growth.

METHODS

Parameters of Kosugi's lognormal PSD model were determined by inverse estimation in a column experiment with two cover crops (mustard, rye) and an unplanted control. Pore dynamics were described using a convection-dispersion like pore evolution model.

RESULTS

Rooted treatments showed a wider range of pore radii with increasing volumes of large macropores >500 μm and micropores <2.5 μm, while fine macropores, mesopores and larger micropores decreased. The non-rooted control showed narrowing of the PSD and reduced porosity over all radius classes. The pore evolution model accurately described root induced changes, while structure degradation in the non-rooted control was not captured properly. Our study demonstrated significant short term root effects with heterogenization of the pore system as dominant process of root induced structure formation.

CONCLUSIONS

Pore clogging is suggested as a partial cause for reduced pore volume. The important change in micro- and large macropores however indicates that multiple mechanic and biochemical processes are involved in root-pore interactions.

[Studies on the allergenic potential of palladium alloys]

Epicutaneous tests with test solutions of the European standard series and palladium chloride (1%) were performed in 486 patients of the University Hospital for Dermatology in Aachen. 17.9% of the patients exhibited Ni, 8.6% Co, 7.4% Pd and 4.1% Cr allergy. In 18 of 36 patients with a positive patch test reaction a further epicutaneous and epimucosal testing with metallic plates of pure palladium and a palladium alloy was performed. In 34 cases a positive skin reaction to palladium chloride was combined with a positive skin reaction to nickel sulphate. Only in one case was it possible to demonstrate an allergic reaction to a palladium metallic plate, which was tested additionally in artificial saliva. The results show that a dental alloy envisaged for use should be tested in an epicutaneous test, if the patient shows a positive reaction to the metallic salt solution. In case of positive patch tests to nickel sulphate, dental palladium alloys should not be used as an alternative unless sensitivity to palladium has been tested.

Influence of systemic ascorbic acid treatment on metabolite levels after regeneration of the corneal epithelium following mild alkali burns

Between 6 and 16 days after mild alkali burns of rabbit eyes, the aqueous humor and corneal stroma ascorbic acid levels were decreased in the untreated animals. Systemic treatment with ascorbate 0.5 g/kg body weight injected daily subcutaneously) raised the reduced ascorbic acid levels to twice the normal values in the aqueous humor, but those of the corneal stroma increased only slightly and remained far below the normal levels. The systemic ascorbate treatment did not improve the healing rate of the corneal epithelium, but increased adenosine triphosphate and diphosphate levels as well as the ATP/ADP ratio of the glutathione was shifted to a more reduced state.