Bias and uncertainty of delta13CO 2 isotopic mixing models

Patterns in the isotopic signal (stable C isotope composition; delta(13)C) of respiration (delta(13)C(R)) have led to important gains in understanding the C metabolism of many systems. Contained within delta(13)C(R) is a record of the C source mineralized, the metabolic pathway of C and the environmental conditions during which respiration occurred. Because gas samples used for analysis of delta(13)C(R) contain a mixture of CO(2) from respiration and from the atmosphere, two-component mixing models are used to identify delta(13)C(R). Measurement of ecosystem delta(13)C(R), using canopy airspace gas samples, was one of the first applications of mixing models in ecosystem ecology, and thus recommendations and guidelines are based primarily on findings from these studies. However, as mixing models are applied to other experimental conditions these approaches may not be appropriate. For example, the range in [CO(2)] obtained in gas samples from canopy air is generally less than 100 micromol mol(-1), whereas in studies of respiration from soil, foliage or tree stems, the range can span as much as 10,000 micromol mol(-1) and greater. Does this larger range in [CO(2)] influence the precision and accuracy of delta(13)C(R) estimates derived from mixing models? Does the outcome from using different regression approaches and mixing models vary depending on the range of [CO(2)]? Our research addressed these questions using a simulation approach. We found that it is important to distinguish between large (>1,000 micromol mol(-1)) and small (<100 micromol mol(-1)) ranges of CO(2) when applying a mixing model (Keeling plot or Miller-Tans) and regression approach (ordinary least squares or geometric mean regression) combination to isotopic data. The combination of geometric mean regression and the Miller-Tans mixing model provided the most accurate and precise estimate of delta(13)C(R) when the range of CO(2) is >or=1,000 micromol mol(-1).

Genetic transformation: a powerful tool for dissection of adaptive traits in trees

Plant transformation and regeneration systems have become indispensable parts of gene discovery and functional characterization over the last two decades. Adoption of transformation methods in studies of plant adaptation to natural environments has been slow. This is a result of poor genomic knowledge and inefficient transformation systems for species dominating terrestrial ecosystems, and logistical difficulties in conducting field tests of genetically engineered organisms. In trees, where long generation cycles, high background polymorphism, large sizes and outcrossing systems of mating make production of near-isogenic lines and large experiments difficult, transformation is an attractive alternative for establishing direct linkages between genes and adaptively significant phenotypes. Here, we outline the capabilities, challenges, and prospects for transformation to become a significant tool for studying the ecophysiological adaptation of trees to the environment. Focusing on poplars (genus Populus) as model system, we describe how transformation-based approaches can provide insights into the genes that control adaptive traits. The availability of the poplar genome sequence, along with its large expressed sequences tag (EST) databanks, facile transformation and rapid growth, enable reverse genetic approaches to be used to test virtually any hypothesis of gene function.

Efficacy of burning, tillage, and biocides in controlling bacteria released at field sites and effects on indigenous bacteria and fungi

Decontamination treatments of burning and biocide application, alone and in combination with tillage, were evaluated for their ability to reduce populations of bacteria applied to the leaves of plants in field plots. In addition, the effects of these control methods on indigenous leaf and soil bacteria and fungi were assessed. Field plots of bush beans (Phaseolus vulgaris), sprayed with the bacterium Pseudomonas syringae, Pseudomonas fluorescens, or Erwinia herbicola, received the following treatments: (i) control, (ii) tillage, (iii) burning, (iv) burning plus tillage (burn-tillage), (v) Kocide (cupric hydroxide), (vi) Kocide plus tillage, (vii) Agri-Strep (streptomycin sulfate), and (viii) Agri-Strep plus tillage. Leaves and soil from the plots were sampled at 1 day before and at 1, 3, 7, 10, 14, 21, and 30 days after application of the decontamination treatments. The burn and burn-tillage treatments produced the most significant reductions in bacterial populations. The Agri-Strep treatment was more effective than the Kocide treatment in eliminating applied bacteria, but neither biocide produced consistent or persistent control. In contrast, the tillage treatment, alone or in combination with the Agri-Strep or Kocide treatments, had a short-term stimulatory effect and increased populations of applied bacteria and also levels of indigenous fungi and bacteria. Agri-Strep and Kocide treatments caused significant reductions in indigenous bacterial populations up to 14 days after application and in indigenous fungal populations on day 7 after application. Our results suggest that conventional plant disease control methods may not provide satisfactory control of genetically engineered microorganisms and indicate a need for further development of effective and selective methods to control release microorganisms at field sites.

Resuscitation effects of catalase on airborne bacteria

Catalase incorporation into enumeration media caused a significant increase (greater than 63%) in the colony-forming abilities of airborne bacteria. Incubation for 30 to 60 min of airborne bacteria in collection fluid containing catalase caused a greater than 95% increase in colony-forming ability. However, catalase did not have any effects on enumeration at high relative humidities (80 to 90%).

[Multiple myeloma and occupational risk factors: a case-control study]

In order to identify possible relationships between multiple myeloma (MM) and occupational factors, a hospital-based case control type study was carried out on 94 cases of MM and on 188 controls matched for sex, age (S.D. = 2 years) and area of residence, suffering from orthopaedic trauma and free of chronic/degenerative or tumoral diseases. All jobs done for at least a year in a period of 5-30 years before diagnosis were considered. Statistical analysis showed a significant correlation between MM and agricultural work (OR 1.82; I.C. 95% 1.03-3.25), which agrees with the data in the literature. The etiopathogenetic hypotheses reported in the literature are discussed and proposals for further research are made.

Trajectory of aerosol droplets from a sprayed bacterial suspension

Simulated droplet trajectories of a polydispersed microbial aerosol in a laminar air flow regimen were compared with observed dispersal patterns of aerosolized Bacillus subtilis subsp. niger spores in quasilaminar airflow. Simulated dispersal patterns could be explained in terms of initial droplet sizes and whether the droplets evaporated to residual aeroplanktonic size before settling to the ground. For droplets that evaporated prior to settling out, a vertical downwind size fractionation is predicted in which the microbial residue of the smallest droplets settles the least, and is found in the airstream at about sprayer height, and progressively larger droplet residues settle to progressively lower heights. Observations of spore particle size distributions downwind from a spray source support the simulation. Droplet and particle size distributions near the source had three size fractions: one containing large, presumably nonevaporated droplets of greater than or equal to 7 microns in diameter, and two smaller fractions, with diameters of 2 to 3 microns (probably the residue of droplets containing more than one spore) and 1 to 2 microns (probably the residue from single-spore droplets). As predicted by the simulation, the aerosol settled and progressed downwind, with the number of small droplets and particles increasing in proportion to the height and distance downwind.