Database of diazotrophs in global ocean: abundance, biomass and nitrogen fixation rates

Marine N2 fixing microorganisms, termed diazotrophs, are a key functional group in marine pelagic ecosystems. The biological fixation of dinitrogen (N2) to bioavailable nitrogen provides an important new source of nitrogen for pelagic marine ecosystems and influences primary productivity and organic matter export to the deep ocean. As one of a series of efforts to collect biomass and rates specific to different phytoplankton functional groups, we have constructed a database on diazotrophic organisms in the global pelagic upper ocean by compiling about 12 000 direct field measurements of cyanobacterial diazotroph abundances (based on microscopic cell counts or qPCR assays targeting the nifH genes) and N2 fixation rates. Biomass conversion factors are estimated based on cell sizes to convert abundance data to diazotrophic biomass. The database is limited spatially, lacking large regions of the ocean especially in the Indian Ocean. The data are approximately log-normal distributed, and large variances exist in most sub-databases with non-zero values differing 5 to 8 orders of magnitude. Reporting the geometric mean and the range of one geometric standard error below and above the geometric mean, the pelagic N2 fixation rate in the global ocean is estimated to be 62 (52–73) Tg N yr?1 and the pelagic diazotrophic biomass in the global ocean is estimated to be 2.1 (1.4–3.1) Tg C from cell counts and to 89 (43–150) Tg C from nifH-based abundances. Reporting the arithmetic mean and one standard error instead, these three global estimates are 140 ± 9.2 Tg N yr?1, 18 ± 1.8 Tg C and 590 ± 70 Tg C, respectively. Uncertainties related to biomass conversion factors can change the estimate of geometric mean pelagic diazotrophic biomass in the global ocean by about ±70%. It was recently established that the most commonly applied method used to measure N2 fixation has underestimated the true rates. As a result, one can expect that future rate measurements will shift the mean N2 fixation rate upward and may result in significantly higher estimates for the global N2 fixation. The evolving database can nevertheless be used to study spatial and temporal distributions and variations of marine N2 fixation, to validate geochemical estimates and to parameterize and validate biogeochemical models, keeping in mind that future rate measurements may rise in the future. The database is stored in PANGAEA (doi:10.1594/PANGAEA.774851)

Phototrophic biofilms and their potential applications

Phototrophic biofilms occur on surfaces exposed to light in a range of terrestrial and aquatic environments. Oxygenic phototrophs like diatoms, green algae, and cyanobacteria are the major primary producers that generate energy and reduce carbon dioxide, providing the system with organic substrates and oxygen. Photosynthesis fuels processes and conversions in the total biofilm community, including the metabolism of heterotrophic organisms. A matrix of polymeric substances secreted by phototrophs and heterotrophs enhances the attachment of the biofilm community. This review discusses the actual and potential applications of phototrophic biofilms in wastewater treatment, bioremediation, fish-feed production, biohydrogen production, and soil improvement

Physical activity after stroke and spinal cord injury

Conditions such as stroke and spinal cord injury (SCI) reduce the ability to activate muscle and produce movement, typically affecting a patient’s functional capacity and ability to carry out the tasks of daily living. Mobility limitations increase the risk of other avoidable chronic conditions such as cardiovascular disease, diabetes, cancer, osteoporosis, and depression, with dramatic negative effects on the overall quality of life. Appropriately prescribed exercise programs are needed to improve health status and overall quality of life for such individuals.1–3 Most authors now agree that moderate physical activity (PA) is well tolerated by such patients, and it seems to have few adverse side effects or contraindications when compared with common pharmacologic interventions.4 There are approximately 50 000 cerebrovascular accidents in Canada each year,5 and although stroke is only the third leading cause of death in North America, it is the leading cause of disability.6 There are more than 85 000 Canadians with SCI, and this number is projected to increase at a rate of approximately 3000 per year.7 Management of these conditions is thus a priority for today’s family physician. A large number of stroke and SCI survivors who could benefit greatly from a suitable program of PA are barred from participation because of incorrect perceptions about their functional capacity and undue concern about causing further harm. Commonly expressed concerns are exacerbation of spasticity and contractures, perceived inability to perform basic movements safely, and a substantial risk of falling. The notion that exercise (particularly resistance training) might exacerbate spasticity has now been refuted,8,9 and there is good evidence that individually tailored resistance or aerobic exercise programs can be performed safely after stroke or SCI.10–14 If such programs are not initiated, the reduced ability for movement and perceived barriers to exercise commonly lead to a progressive decrease in the individual’s overall PA, with all the adverse effects of concomitant physical deconditioning. This article provides an executive summary of findings from a systematic review of the risks of PA in stroke and SCI.15 It was undertaken as one in a comprehensive series of reviews examining the risks of PA in various chronic diseases. The evidence thus obtained provides the foundation for new tools to be used in exercise clearance: the revised Physical Activity Readiness Questionnaire (PAR-Q+) and the electronic Physical Activity Readiness Medical Examination (ePARmed-X+) procedure.16 We briefly discuss available data on the risks of PA in stroke and SCI, and present decision trees that facilitate the family physician’s task of setting appropriate PA prescription and guidelines for the ongoing monitoring of patients