Management impacts on the dissolved organic carbon release from deadwood, ground vegetation and the forest floor in a temperate Oak woodland

The forest floor is often considered the most important source of dissolved organic carbon (DOC) in forest soils, yet little is known about the relative contribution from different forest floor layers, understorey vegetation and deadwood. Here, we determine the carbon stocks and potential DOC production from forest materials: deadwood, ground vegetation, leaf litter, the fermentation layer and top mineral soil (Ah horizon), and further assess the impact of management. Our research is based on long-term monitoring plots in a temperate deciduous woodland, with one set of plots actively managed by thinning, understorey scrub and deadwood removal, and another set that were not managed in 23 years. We examined long-term data and a spatial survey of forest materials to estimate the relative carbon stocks and concentrations and fluxes of DOC released from these different pools. Long-term soil water monitoring revealed a large difference in median DOC concentrations between the unmanaged (43.8 mg L^-1) and managed (18.4 mg L^-1) sets of plots at 10 cm depth over six years, with the median DOC concentration over twice as high in the unmanaged plots. In our spatial survey, a significantly larger cumulative flux of DOC was released from the unmanaged than the managed site, with 295.5 and 230.3 g m^-2, respectively. Whilst deadwood and leaf litter released the greatest amount of DOC per unit mass, when volume of the material was considered, leaf litter contributed most to DOC flux, with deadwood contributing least. Likewise, there were significant differences in the carbon stocks held by different forest materials that were dependent on site. Vegetation and the fermentation layer held more carbon in the managed site than unmanaged, whilst the opposite occurred in deadwood and the Ah horizon. These findings indicate that management affects the allocation of carbon stored and DOC released between different forest materials.

Abnormal eating attitudes in secondary-school girls in South Africa--a preliminary study

OBJECTIVES

To document the existence of eating attitudes that may reflect current, pre- or subclinical eating disorders. To establish preliminary prevalence figures for abnormal eating attitudes.

DESIGN

Cross-sectional survey of eating attitudes.

SETTING

Non-clinical, community-based.

SUBJECTS

Female high-school pupils.

OUTCOME MEASURES

Total score derived from a self-report questionnaire, Eating Attitudes Test (EAT-26), which measures eating attitudes. Factor profile describing dimensions of eating-related psychopathology, derived from the clustering of questions on the EAT-26.

RESULTS AND CONCLUSIONS

An overall prevalence figure of abnormal eating attitudes of 21.66% was documented. Black pupils had a higher prevalence than white pupils (37.5% v. 20.67%). The factor profile of respondents with abnormal eating attitudes did not differ between the race groups, although within the total sample, black respondents had a significantly stronger drive toward thinness. A significant developmental continuum was established, with prevalence figures for abnormal eating attitudes increasing with each standard from Standard 7 onward. The study provides preliminary epidemiological data on the prevalence of adolescent girls either suffering from or at risk of the development of an eating disorder. In addition, the study also provides evidence of the need for intervention strategies that commence in the pre-teen years.

Factors influencing eating attitudes in secondary-school girls in South Africa--a preliminary study

OBJECTIVES

To establish factors in the environment, e.g. family, peer or media, as well as individual factors, e.g. self-perception, which may influence eating attitudes.

DESIGN

Cross-sectional survey.

SETTING

Non-clinical, community-based.

SUBJECTS

Female high-school pupils.

OUTCOME MEASURES

Responses to questions pertaining to environmental as well as individual factors for each respondent ('dieting questionnaire'; self report). Total scores derived from a self-report questionnaire pertaining to eating attitudes (Eating Attitudes Test (EAT-26)). Statistical analysis, using analysis of variance procedures, to determine significant associations between the two questionnaires.

RESULTS AND CONCLUSIONS

Specific individual wishes, perceptions, behaviours and topics of conversation appear to influence as well as predict eating attitudes. Family, especially maternal, factors play a role in determining eating attitudes. Peer and media (television) factors are not significantly influential. The findings provide preliminary data on factors that influence eating attitudes in a group at risk for the development of eating disorders. The findings have implications for the formulation of preventive strategies within a comprehensive treatment approach.

N-alkylation of the haem moiety of cytochrome P-450 caused by substituted dihydropyridines. Preferential attack of different pyrrole nitrogen atoms after induction of various cytochrome P-450 isoenzymes

1. 3,5-Diethoxycarbonyl-4-ethyl-1,4-dihydro-2,6-dimethylpyridine (4-ethyl-DDC) gives rise to N-ethylprotoporphyrin in the liver of rats by donating its 4-ethyl group to one of the pyrrole nitrogen atoms of haem. Four structural isomers are obtained, depending on which pyrrole nitrogen is alkylated. 2. When rats are pretreated with an inducer of cytochrome P-450, the production of N-ethylprotoporphyrin caused by 4-ethyl-DDC is greater, both in the whole animal and in hepatocytes incubated with the drug in vitro. 3. Pre-incubation of hepatocytes with 2-allyl-2-isopropylacetamide decreases the yield of N-ethylprotoporphyrin due to 4-ethyl-DDC, an effect largely reversed by adding exogenous haem. 4. The isomeric composition of N-ethylprotoporphyrin produced in vivo and in vitro depends on the cytochrome P-450 isoenzyme that predominates at the time of treatment, suggesting a role for the apo-cytochrome in directing alkylation on to one of the pyrrole nitrogens.