The contributions of enchytraeids and earthworms to the soil mineralization process in soils with fungicide

Pesticides may harm soil organisms such as earthworms and enchytraeids, but knowledge is lacking on their relative sensitivity to these chemicals and the consequences on soil functions. The aim of this study was to assess the impact of exposure to a commercial fungicide formulation (Swing® Gold, containing dimoxystrobin and epoxiconazole) on the function of earthworms (Aporrectodea caliginosa) and enchytraeids (Enchytraeus buchholzi) in soil organic matter (SOM) mineralization. The soil organisms were incubated alone and together in a 26-day laboratory experiment. At the recommended field rate, the fungicide induced a decrease in the SOM mineralization and a delay in the maximum daily CO₂ emissions compared to the control soil without fungicide. Soil fauna also influenced SOM mineralization with a higher cumulated CO₂ release after 26 days in the control soil with earthworms (by 21%) than without fauna. When both earthworms and enchytraeids were present, SOM mineralization did not increase, and there was a negative effect on earthworm weight gain. Finally, an alteration of fauna influence with treatment was observed from day 19, meaning that the effect of fauna on SOM mineralization changed with fungicide treatment. Earthworms no longer promoted SOM mineralization when fungicide was present at three-fold the recommended field rate. The effects of enchytraeids on SOM mineralization were similar with and without fungicide exposure. This study underlines the importance of considering the relative sensitivity of soil organisms to environmental factors and interactions between them when assessing soil functioning.

Spatio-temporal analysis of infra-specific genetic variations among a Pseudomonas aeruginosa water network hospital population: invasion and selection of clonal complexes

AIMS

To investigate infra-specific spatio-temporal dynamics of a hospital water network Pseudomonas aeruginosa population. To infer the origin of water network isolates and assess their potential health hazard.

METHODS AND RESULTS

168 P. aeruginosa strains were isolated from tap waters and swabs of tap nozzle aerators of a hospital unit, over 2 years, and from rectal swabs and nosocomial infections. Genetic diversity among this collection was assessed by pulsed field gel electrophoresis of SpeI restricted genomic DNA. Virulence gene sets, biofilm properties, and hypochlorite resistance were analysed. Exactly 68% of the water samples and 74% of the tap nozzle aerators harboured P. aeruginosa. The strains were divided into 22 clonal lineages, with one dominant clone shown to have been involved in a nosocomial infection.

CONCLUSIONS

An important turnover among the P. aeruginosa hospital population was observed. Some clonal lineages were found to persist, spread in the unit, and diversify into clonal complexes. Rectal carriage appeared an important source of contamination of the water network.

SIGNIFICANCE AND IMPACT OF THE STUDY

High P. aeruginosa infra-specific population diversity suggested a broad ability in colonizing water networks but persistence analysis indicated a strong selection leading to the emergence of dominant clones.

Temporal envelope expansion of speech in noise for normal-hearing and hearing-impaired listeners: effects on identification performance and response times

The effects of expanding the temporal envelope of speech sounds on speech identification in noise were investigated in normal-hearing and hearing-impaired listeners. Expansion was performed by applying a power-law transformation to the low-frequency temporal modulations (<500 Hz) of vowel-consonant-vowel logatomes presented against a background noise. Stimuli were spectrally degraded, allowing a direct examination of the perceptual effects induced by the modification of the temporal envelope alone on speech reception. This study extended a previous study conducted by Lorenzi et al. [1999. Hear. Res. 136, 131--138] by measuring the effects of envelope expansion on both identification performance and response times in normal-hearing and hearing-impaired listeners. Overall, the results show that temporal expansion yields only small improvements in identification scores (approximately 5%) in normal-hearing listeners. No effect of expansion on identification scores was observed in hearing-impaired listeners. On the other hand, the results show that expansion led to a significant decrease in response times in both normal-hearing and hearing-impaired listeners. The average benefit from expansion was about 65 ms in both groups. These results suggest that expanding the temporal envelope of speech sounds presented in noise may improve 'ease of listening' in both normal-hearing and hearing-impaired listeners.