The Effects of Infrared Loading and Water Table on Soil Energy Fluxes in Northern Peatlands

Increased radiative forcing is an inevitable part of global climate change, yet little is known of its potential effects on the energy fluxes in natural ecosystems. To simulate the conditions of global warming, we exposed peat monoliths (depth, 0.6 m; surface area, 2.1 m²) from a bog and fen in northern Minnesota, USA, to three infrared (IR) loading (ambient, +45, and +90 W m^–2) and three water table (–16, –20, and –29 cm in bog and –1, –10 and –18 cm in fen) treatments, each replicated in three mesocosm plots. Net radiation (Rn) and soil energy fluxes at the top, bottom, and sides of the mesocosms were measured in 1999, 5 years after the treatments had begun. Soil heat flux (G) increased proportionately with IR loading, comprising about 3%–8% of Rn. In the fen, the effect of IR loading on G was modulated by water table depth, whereas in the bog it was not. Energy dissipation from the mesocosms occurred mainly via vertical exchange with air, as well as with deeper soil layers through the bottom of the mesocosms, whereas lateral fluxes were 10–20-fold smaller and independent of IR loading and water table depth. The exchange with deeper soil layers was sensitive to water table depth, in contrast to G, which responded primarily to IR loading. The qualitative responses in the bog and fen were similar, but the fen displayed wider seasonal variation and greater extremes in soil energy fluxes. The differences of G in the bog and fen are attributed to differences in the reflectance in the long waveband as a function of vegetation type, whereas the differences in soil heat storage may also depend on different soil properties and different water table depth at comparable treatments. These data suggest that the ecosystem-dependent controls over soil energy fluxes may provide an important constraint on biotic response to climate change.     

Chronic nitrogen additions suppress decomposition and sequester soil carbon in temperate forests

The terrestrial biosphere sequesters up to a third of annual anthropogenic carbon dioxide emissions, offsetting a substantial portion of greenhouse gas forcing of the climate system. Although a number of factors are responsible for this terrestrial carbon sink, atmospheric nitrogen deposition contributes by enhancing tree productivity and promoting carbon storage in tree biomass. Forest soils also represent an important, but understudied carbon sink. Here, we examine the contribution of trees versus soil to total ecosystem carbon storage in a temperate forest and investigate the mechanisms by which soils accumulate carbon in response to two decades of elevated nitrogen inputs. We find that nitrogen-induced soil carbon accumulation is of equal or greater magnitude to carbon stored in trees, with the degree of response being dependent on stand type (hardwood versus pine) and level of N addition. Nitrogen enrichment resulted in a shift in organic matter chemistry and the microbial community such that unfertilized soils had a higher relative abundance of fungi and lipid, phenolic, and N-bearing compounds; whereas, N-amended plots were associated with reduced fungal biomass and activity and higher rates of lignin accumulation. We conclude that soil carbon accumulation in response to N enrichment was largely due to a suppression of organic matter decomposition rather than enhanced carbon inputs to soil via litter fall and root production.     

Resistance exercise and cyclooxygenase (COX) expression in human skeletal muscle: implications for COX-inhibiting drugs and protein synthesis

We have shown that ibuprofen and acetaminophen block cyclooxygenase (COX) synthesis of prostaglandin PGF(2alpha) and the muscle protein synthesis increase following resistance exercise. Confusingly, these two drugs are purported to work through different mechanisms, with acetaminophen apparently unable to block COX and ibuprofen able to nonspecifically block COX-1 and COX-2. A recently discovered intron-retaining COX, now known to have three variants, has been shown to be sensitive to both drugs. We measured the expression patterns and levels of the intron 1-retaining COX-1 variants (-1b1, -1b2, and -1b3), COX-1, and COX-2 at rest and following resistance exercise to help elucidate the COX through which PGF(2alpha), ibuprofen, and acetaminophen regulate muscle protein synthesis. Skeletal muscle biopsy samples were taken from 16 individuals (8M, 8F) before, 4, and 24 h after a bout of resistance exercise and analyzed using real-time RT-PCR. Relatively few individuals expressed the intron 1-retaining COX-1b variants (COX-1b1, -1b2, and -1b3) at any time point, and when expressed, these variants were in very low abundance. COX-1 was the most abundant COX mRNA before exercise and remained unchanged (P > 0.05) following exercise. COX-2 was not expressed before exercise, but increased significantly (P < 0.05) at 4 and 24 h after exercise. The inconsistent and low levels of expression of the intron 1-retaining COX-1 variants suggest that these variants are not likely responsible for the inhibition of PGF(2alpha) production and skeletal muscle protein synthesis after resistance exercise by ibuprofen and acetaminophen. Skeletal muscle-specific inhibition of COX-1 or COX-2 by these drugs should be considered.     

Photochemistry of dyes and fluorochromes used in biology and medicine: some physicochemical background and current applications

An overview of the basic principles of photochemistry is presented to facilitate discussion of fluorescence, quenching and quantum yields. These topics in turn provide the foundation for an account of fluorescence spectroscopy and its application to microscopy. A brief overview of light microscopy and the application of fluorescence microscopy is given. The influences of molecular features, such as aromatic character and substitution patterns, on color and fluorescence are described. The concept of color fading is considered with particular reference to its effect on microscopic preparations. A survey of representative fluorescent probes is provided, and their sensitivity, application, and limitations are described. The phototoxicity of fluorescent molecules is discussed using biomembranes and DNA as examples of targets of toxicity. Photodynamic therapy, a relatively new clinical application of phototoxicity, is described. Both anticancer and antimicrobial applications are noted, and an assessment is given of the current ideas on the ideal physicochemical properties of the sensitizing agents for such applications.     

Cortisol stress response and histopathological alteration index in Clarias gariepinus exposed to sublethal concentrations of Qua Iboe crude oil and rig wash

The histological effect on and stress response of post juvenile Clarias gariepinus exposed to Qua Iboe crude oil and rig wash were investigated. Fish weighing 60–90 g and measuring 16–18 cm were exposed for 7–28 days to 8.00 ml^?1 Qua Iboe crude oil and 0.0018 ml^–1 rig wash, both being 0.1 of the 96 hr LC₅₀. Blood samples of C. gariepinus were collected every seven days and evaluated for stress by measuring cortisol concentration. The gills and liver were studied and scored for Gill Alteration Index (GAI) and Hepatic Alteration Index (HAI), respectively. There was an increase in cortisol level up to the 7th and 14th day among the group exposed to Qua Iboe crude oil, with a decrease on the 21st and 28th day. The rig wash group increased in cortisol level up to the 7th day and decreased slightly on the 14th day, after which the trend became irregular. The toxic effects of the Qua Iboe crude oil and rig wash were time dependent, as shown by the histopathological alteration index (HAI) of gill and liver. After 28 days of exposure, the gills had irreparable damage due to high frequency of cellular necrosis and degeneration, whereas the liver had from moderate to severe damage due to the high frequency of cellular degeneration and inflammation. Qua Iboe crude oil and rig wash are both toxic to C. gariepinus, therefore their indiscriminate discharge to the environment must be discouraged.     

Molecular-level changes in soil organic matter composition after 10 years of litter,root and nitrogen manipulation in a temperate forest

With climate change, forests are expected to receive increased inputs of carbon (C) and nitrogen (N) but it is unclear how this will modify forest C cycling and storage at the molecular-level. To investigate the response of forest soil organic matter (SOM) to changes in soil inputs, a study area was established in a Michigan hardwood forest as part of the Detrital Input and Removal Treatments (DIRT) network. Experimental treatments were comprised of both exclusions of detrital inputs (No Litter, No Roots, No Inputs) and additions of C and N (Double Litter, N-Addition, Double Litter?+?N, Wood). After 10 years of treatment, the soils were characterized using elemental analysis, molecular biomarker techniques, nuclear magnetic resonance spectroscopy, and microbial biomass C measurements. Although manipulation of detrital inputs did not significantly change the soil C and N content after 10 years, alterations in the cycling and distribution of SOM components were observed. Root exclusion enhanced SOM degradation, while doubling litter favoured the degradation of more labile forms of soil C such as unsaturated n-alkanoic acids and simple sugars. N-Addition and Double Litter?+?N increased the concentrations of extractable biomarkers, including aliphatic and cyclic lipids and compounds derived from cutin, suberin, and lignin. Microbial biomass C also varied with experimental litter input manipulations and N addition, and these data were consistent with the observed changes in SOM composition. Overall, the observed shifts in SOM chemistry after 10 years of manipulating ecosystem inputs highlight the sensitivity of natural systems to changes in amounts of C and N inputs from roots and litter, and N inputs from external sources.