Field calibration of soil-core microcosms: Ecosystem structural and functional comparisons

Abstract

Microcosms containing intact soil-cores are a potential biotechnology risk assessment tool for assessing the ecological effects of genetically engineered microorganisms before they are released to the field; however, microcosms must first be calibrated to ensure that they adequately simulate key field parameters. Soil-core microcosms were compared with the field in terms of ecological response to the introduction of a large inoculum of a rifampicin-resistant rhizobacterium,Pseudomonas sp. RC1. RC1 was inoculated into intact soil-core microcosms incubated in the laboratory at ambient temperature (22°C) and in a growth chamber with temperature fluctuations that mimicked a verage field values, as well as into field lysimeters and plots. The effect of the introduced bacterium on ecosystem structure, including wheat rhizoplane populations of total and fluorescent pseudomonads, total heterotrophic bacteria, and the diversity of total heterotrophic bacteria, was determined. Fluorescent pseudomonads were present on the rhizoplane in significantly lower numbers in soil inoculated with RC1, in both microcosms and the field. Conditions for microbial growth appeared to be most favorable in the growth chamber microcosm, as evidenced by higher populations of heterotrophs and a greater species diversity on the rhizoplane at the three-leaf stage of wheat growth. Ecosystem functional parameters, as determined by soil dehydrogenase activity, plant biomass production, and(15)N-fertilizer uptake by wheat, were different in the four systems. The stimulation of soil dehydrogenase activity by the addition of alfalfa was greater in the microcosms than in the field. In general, growth chamber microcosms, which simulated average field temperatures, were better predictors of field behavior than microcosms incubated continuously at 22°C.

Effect of Field Inoculation with Sinorhizobium meliloti L33 on the Composition of Bacterial Communities in Rhizospheres of a Target Plant ( Medicago sativa ) and a Non-Target Plant ( Chenopodium album )—Linking of 16S rRNA Gene-Based Single-Strand Conformation Polymorphism Community Profiles to the Diversity of Cultivated Bacteria

“…Pseudomonas spp. were also displaced in rhizosphere communities in other studies (5,13). It was suggested that this effect is related to the potential for fast growth, which allows the organisms to respond quickly to changing conditions in the rhizosphere (13).…”

“…In our study, we wanted to determine whether the composition of the bacterial types in rhizospheres was affected by inoculation with S. meliloti. Transiently occurring changes in microbial community structure in response to inoculation have been detected in studies performed with nonsymbiotic rhizosphere bacteria (5,13,40,41). To understand the importance of the symbiotic relationship, we included analyses of bacterial populations in the rhizospheres of a host plant, M. sativa, and a nonhost plant, the weed C. album.…”

Impact of 2,4-Diacetylphloroglucinol-Producing Biocontrol Strain Pseudomonas fluorescens F113 on Intraspecific Diversity of Resident Culturable Fluorescent Pseudomonads Associated with the Roots of Field-Grown Sugar Beet Seedlings

“…Inoculation of soil or seeds with pseudomonads for biocontrol purposes implies the release of cells in large numbers (often higher than the number of RCFP), which can cause a transient increase in the number of total culturable fluorescent pseudomonads (1,49) and even sometimes in that of total culturable aerobic bacteria (4,49). At 19 days after sowing, the number of total culturable fluorescent pseudomonads at the rhizoplane was not affected, but that of RCFP was reduced (Table 1), similar to the results of other studies (10,36,47).…”

Microbial trophic interactions in aquatic microcosms designed for testing genetically engineered microorganisms: A field comparison

“…Before microcosms can be used as a risk assessment tool they must first be calibrated with field observations to ensure a reliable extrapolation of experimental results [3]. The objective of this study was to field calibrate an aquatic microcosm.…”