A standardized quantitative approach was developed to reliably elucidate the effect of increasing soil moisture on pesticide mineralization. The mineralization of three aerobically degradable and chemically different 14C-labeled pesticides (isoproturon, benazolin-ethyl, and glyphosate) was studied under controlled conditions in the laboratory at an identical soil density of 1.3 g cm(-3). The agricultural soils used are characterized by (i) large variations in soil texture (sand content 4-88%) and organic matter content (0.97-2.70% org. C), (ii) fairly diverse soil-water retention curves, and (iii) differing pH values. We quantified the effect of soil moisture on mineralization of pesticides and found that (i) at soil water potential < or = -20 MPa minimal pesticide mineralization occurred; (ii) a linear correlation (P < 0.0001) exists between increasing soil moisture (within a soil water potential range of -20 and -0.015 MPa), and increased relative pesticide mineralization; (iii) optimum pesticide mineralization was obtained at a soil water potential of -0.015 MPa, and (iv) when soil moisture approximated water holding capacity, pesticide mineralization was considerably reduced. As both selected pesticides and soils varied to a large degree, we propose that the correlation observed in this study may be also valid in the case of aerobic degradation of other native and artificial organic compounds in soils.

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The genus Herbaspirillum of the Betaproteobacteria mainly comprises diazotrophic bacteria with a potential for endophytic and systemic colonization of a variety of plants. The plant-associated bacterial isolates N3 T , N5 and N9 were derived from surface-sterilized wheat roots. After phylogenetic analysis of 16S rRNA gene sequence data the isolates could be allocated to the genus Herbaspirillum, and 99?9 % similarity to the sequence of Herbaspirillum lusitanum P6-12 T was found. A set of 16S rRNA gene-targeted oligonucleotide probes was developed for the identification of the three novel isolates and H. lusitanum (Hhilu446), and for the specific detection of several other Herbaspirillum species described recently. For higher phylogenetic resolution, the 23S rRNA gene sequences of all members of the genus was sequenced and used to construct a phylogenetic tree. Isolates N3 T , N5 and N9 formed a group that was distinct from all other Herbaspirillum species. In addition, isolate N3T and H. lusitanum P6-12 T exhibited a DNA-DNA hybridization value of only 25 %. The value for DNA-DNA hybridization between N3 T and other members of the genus Herbaspirillum was between 14 and 32 %; DNA-DNA hybridization between strain N3 T and isolates N5 and N9 produced values above 95 %. This places the three isolates as representatives of a novel species within the genus Herbaspirillum. A Biolog GN2 assay supported this conclusion. The major fatty acids were C 16 : 1 v7c, C 16 : 0 and C 18 : 1 v7c, and the DNA G+C content ranged from 60?9 to 61?5 mol%. Therefore these three isolates should be classified within a novel species, for which the name Herbaspirillum hiltneri sp. nov. is proposed. The type strain is N3 T (=DSM 17495 T =LMG 23131 T ).On the basis of comparative sequence analysis of rRNAencoding genes, the genus Herbaspirillum is affiliated phylogenetically to the Betaproteobacteria (Schmid et al., 2005). The genus was first described with the species Herbaspirillum seropedicae (Baldani et al., 1986), which has been isolated from rice, maize and sorghum plants. After detailed taxonomic studies, the mildly plant-pathogenic [Pseudomonas] rubrisubalbicans was reclassified to the genus Herbaspirillum as Herbaspirillum rubrisubalbicans (Baldani et al., 1996).Another species of this genus, Herbaspirillum frisingense, was isolated from the C4-fibre plants Miscanthus spp., Spartina spectinata and Pennisetum purpureum by Kirchhof et al. (2001). From root nodules of garden beans (Phaseolus vulgaris), several strains representing one distinct species were isolated and described as Herbaspirillum lusitanum (Valverde et al., 2003). These root-colonizing Herbaspirillum species were detected not only on the surface of the root, but also as intra-and intercellular colonizers in the root interior (Olivares et al., 1997). These bacteria seem to prefer plants of the family Gramineae as hosts (Kirchhof et al., 2001), but they are also found on other plant species (Baldani et al., 1996). According to Döbereiner et al. (1993), the close associa...

In a risk assessment study the environmental fate of the herbicide glyphosate was studied with the specific background of the presence of genetically modified (GM) plants. Aim was to simulate the environmental behaviour of glyphosate in sandy field soil lysimeters after multiple herbicide applications and under the presence of GM soybean and to test and enhance model reliability in the simulation of the herbicide fate including biodegradation in the soil and herbicide translocation in GM plants. The modelling of the herbicide behaviour in the present study was based on the pesticide transport model LEACHP and the model PLANTX to simulate the pesticide uptake by plants. Both models were implemented in the modular modelling system EXPERT-N. Glyphosate transport measurements and the mathematical modelling results indicate that due to the high sorption of glyphosate to the soil matrix and the high microbial capacities for glyphosate degradation in the lysimeter soil, leaching risk can be considered to be low. We confirmed that the introduction of more adequate conceptual descriptions of microbial response to pesticide and nutrient additions can contribute to a reduction in the uncertainty of pesticide degradation modelling. Moreover, the consideration of uncertainty in sorption, dispersivity and degradation parameters revealed a considerable variability in model output. The observed accumulation of glyphosate in roots and nodules was reproduced by the simulation results. Under the restriction that the prevailing model assumptions are valid, the simulation results indicate that glyphosate may accumulate also in beans of trangenic soybean.

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