Soil 13C–15N dynamics in an N2-fixing clover system under long-term exposure to elevated atmospheric CO2

Reduced soil N availability under elevated CO₂ may limit the plant's capacity to increase photosynthesis and thus the potential for increased soil C input. Plant productivity and soil C input should be less constrained by available soil N in an N₂‐fixing system. We studied the effects of Trifolium repens (an N₂‐fixing legume) and Lolium perenne on soil N and C sequestration in response to 9 years of elevated CO₂ under FACE conditions. ¹⁵N‐labeled fertilizer was applied at a rate of 140 and 560 kg N ha^?1 yr^?1 and the CO₂ concentration was increased to 60 Pa pCO₂ using ¹³C‐depleted CO₂. The total soil C content was unaffected by elevated CO₂, species and rate of ¹⁵N fertilization. However, under elevated CO₂, the total amount of newly sequestered soil C was significantly higher under T. repens than under L. perenne. The fraction of fertilizer‐N (f_N) of the total soil N pool was significantly lower under T. repens than under L. perenne. The rate of N fertilization, but not elevated CO₂, had a significant effect on f_N values of the total soil N pool. The fractions of newly sequestered C (f_C) differed strongly among intra‐aggregate soil organic matter fractions, but were unaffected by plant species and the rate of N fertilization. Under elevated CO₂, the ratio of fertilizer‐N per unit of new C decreased under T. repens compared with L. perenne. The L. perenne system sequestered more ¹⁵N fertilizer than T. repens: 179 vs. 101 kg N ha^?1 for the low rate of N fertilization and 393 vs. 319 kg N ha^?1 for the high N‐fertilization rate. As the loss of fertilizer‐¹⁵N contributed to the ¹⁵N‐isotope dilution under T. repens, the input of fixed N into the soil could not be estimated. Although N₂ fixation was an important source of N in the T. repens system, there was no significant increase in total soil C compared with a non‐N₂‐fixing L. perenne system. This suggests that N₂ fixation and the availability of N are not the main factors controlling soil C sequestration in a T. repens system.     

Sex differences in heritability of BMI: a comparative study of results from twin studies in eight countries.

Body mass index (BMI), a simple anthropometric measure, is the most frequently used measure of adiposity and has been instrumental in documenting the worldwide increase in the prevalence of obesity witnessed during the last decades. Although this increase in overweight and obesity is thought to be mainly due to environmental changes, i.e., sedentary lifestyles and high caloric diets, consistent evidence from twin studies demonstrates high heritability and the importance of genetic differences for normal variation in BMI. We analysed self-reported data on BMI from approximately 37,000 complete twin pairs (including opposite sex pairs) aged 20-29 and 30-39 from eight different twin registries participating in the GenomEUtwin project. Quantitative genetic analyses were conducted and sex differences were explored. Variation in BMI was greater for women than for men, and in both sexes was primarily explained by additive genetic variance in all countries. Sex differences in the variance components were consistently significant. Results from analyses of opposite sex pairs also showed evidence of sex-specific genetic effects suggesting there may be some differences between men and women in the genetic factors that influence variation in BMI. These results encourage the continued search for genes of importance to the body composition and the development of obesity. Furthermore, they suggest that strategies to identify predisposing genes may benefit from taking into account potential sex specific effects.     

Response of Daphnia to substances released from crowded congeners and conspecifics

The effects of chemicals released from crowded congeners andconspecifics on life history parameters of the freshwater zooplanktersDaphnia cucullata and Daphnia pulex were examined. Length andage at maturity of D. pulex were affected by crowding chemicals.Reproduction was lower in crowded medium, and ephippia wereproduced. Newborn D. pulex in crowded medium were significantlylonger than the controls. The intrinsic rate of population increaseof D. pulex was 14 and 25% lower than the control when exposedto crowded medium from D. cucullata and D. pulex, respectively.Neither urea nor ammonia (at 1 mg l^-1) seemed to be responsiblefor these effects in D. pulex. In D. cucullata, no significanteffect of crowding infochemicals on length and age at maturitywas found. However, crowding chemicals reduced reproduction.No ephippia were produced in crowded medium, but up to 83% non-developingeggs were observed in D. cucullata. Newborns were similarlysized in crowded and standard medium. The intrinsic rate ofpopulation increase of D. cucullata was 44 and 96% lower thanthe control when exposed to crowded medium from D. cucullataand D. pulex, respectively. Clearance rates of D. pulex weresignificantly reduced in crowded media compared with standardmedium, which could partly explain why the animals exposed tocrowding chemicals reacted as if they were food limited.     

The ability of rufous hummingbirds Selasphorus rufus to dilute and concentrate urine

Most terrestrial animals face the challenge of having to conserve water in a desiccating environment. Not surprisingly, the ability to produce concentrated urine has been relatively well studied in birds. Nectar-feeding birds are unusual among terrestrial animals in that they often ingest and excrete prodigious water volumes to obtain adequate energy. Thus, they confront the unusual challenge of having to conserve electrolytes. The diluting abilities of birds and the renal mechanisms that may correlate with them have been relatively neglected. To elucidate diluting and concentrating abilities in nectar-feeding birds, we fed rufous hummingbirds Selasphorus rufus an electrolyte-free nectar and a nectar containing a range of NaCl concentrations. Hummingbirds had a spectacular (and possibly unique) diluting ability: when fed on electrolyte-free food they produced excreta containing less than 0.5 mM l⁻¹ each of sodium and potassium. Hummingbirds also had a poor concentrating ability, retaining sodium and chloride when their food (0.632 M l⁻¹ sucrose) contained more than 35 mM l⁻¹ of NaCl. The kidneys of hummingbirds do not appear to be suited for concentrating urine, and possibly contain structural features that give them a unique diluting ability compared with those of birds that do not feed on nectar.     

Feeding ecology and dietary differences between blue monkey (Cercopithecus mitis stuhlmanni Matschie) groups in logged and unlogged forest, Budongo Forest Reserve, Uganda

Several studies have investigated the effects of logging on primate population density, and attempted to relate density differences to changes in vegetation composition. As population density in some forest primates may be considerably influenced by dietary quality, it is important to understand how the effects of vegetation changes commonly associated with logging influence primate feeding ecology. Results are presented from a study carried out in the Budongo Forest Reserve in Uganda to investigate differences in blue monkey (Cercopithecus mitis stuhlmanni) feeding ecology in forest blocks with different logging history. Dietary composition differed between logged and unlogged forest, with a higher proportion of unripe fruit consumed in logged forest. By contrast, the proportion of young leaves, invertebrates and seeds in the diet was higher in unlogged forest. Variations in the intake of fruit was also higher in unlogged forest, but feeding patterns on other dietary items were more selective. These differences in diet reflect differences in availability of different categories of food items, as determined by tree species composition, abundance and plant phenological patterns. The observed differences between feeding ecology in logged and unlogged forest are discussed in relation to primate feeding ecology and habitat composition in Budongo.     

A misfolded form of 5S rRNA is complexed with the Ro and La autoantigens.

In both vertebrate and invertebrate cells, the 60-kDa Ro autoantigen is bound to small cytoplasmic RNAs known as Y RNAs. In Xenopus oocytes, the 60-kDa Ro protein is also complexed with a class of 5S rRNA precursors that contain internal mutations. Because these 5S rRNA precursors are processed inefficiently and degraded eventually, the Ro protein may function in a quality control pathway for 5S rRNA biosynthesis. We have investigated the sequence and secondary structure determinants in the mutant 5S rRNAs that confer binding by the 60-kDa Ro protein. The mutant 5S rRNAs fold to form an alternative helix that is required for recognition by the 60-kDa Ro protein. Mutations that disrupt the alternative helix eliminate Ro protein binding, whereas compensatory changes that restore the helix are bound efficiently by the Ro protein. When the structure of the mutant RNA was probed using dimethylsulfate and oligonucleotide-directed RNase H cleavage, the results were consistent with the formation of the alternative structure. The La protein, which is also complexed with the mutant 5S rRNA precursors, protects similar sequences from nuclease digestion as does the 60-kDa Ro protein. Thus, the binding sites for these two proteins are either nearby on the RNA, or the two proteins may be complexed through protein-protein interactions. When the human Ro protein is expressed in the yeast Saccharomyces cerevisiae, the protein binds wild-type 5S rRNA precursors, suggesting that a population of wild-type precursors also folds into the alternative structure.     

Effects of temperature,salinity and agitation on byssus thread formation of zebra musselDreissena polymorpha

Byssus thread production ofD. polymorpha under different conditions of temperature, salinity and agitation were studied in the laboratory. The acclimation to salinity and temperature greatly affects the byssus production ofD. polymorpha. Byssus production of mussels was significantly reduced when temperature increased beyond 20°C and decreased below 10°C. Mussels with cut threads (for counting), produced a substantially increased number of threads. However, mussels with uncut byssus threads were comparatively more mobile. Byssus production of mussels did not vary significantly at salinities up to 3. Beyond this salinity byssus production was reduced significantly. Mussels increased their byssus production with increasing frequency of agitation.     

Simultaneous determination of azathioprine and 6-mercaptopurine by high-performance liquid chromatography

A specific, sensitive, single-step solid-phase extraction and reversed-phase high-performance liquid chromatographic method for the simultaneous determination of plasma 6-mercaptopurine and azathioprine concentrations is reported. Following solid-phase extraction, analytes are separated on a C₁₈ column with mobile phase consisting of 0.8% acetonitrile in 1 mM triethylamine, pH 3.2, run on a gradient system. Quantitation limits were 5 ng/ml and 2 ng/ml for azathioprine and 6-mercaptopurine, respectively. Peak heights correlated linearly to known extracted standards for 6-mercaptopurine and azathioprine (r = 0.999) over a range of 2–200 ng/ml. No chromatographic interferences were detected.