Search

The availability of nitrogen represents a key constraint on carbon cycling in terrestrial ecosystems, and it is largely in this capacity that the role of N in the Earth's climate system has been considered. Despite this, few studies have included continuous variation in plant N status as a driver of broad-scale carbon cycle analyses. This is partly because of uncertainties in how leaf-level physiological relationships scale to whole ecosystems and because methods for regional to continental detection of plant N concentrations have yet to be developed. Here, we show that ecosystem C[O.sub.2] uptake capacity in temperate and boreal forests scales directly with whole-canopy N concentrations, mirroring a leaf-level trend that has been observed for woody plants worldwide. We further show that both C[O.sub.2] uptake capacity and canopy N concentration are strongly and positively correlated with shortwave surface albedo. These results suggest that N plays an additional, and overlooked, role in the climate system via its influence on vegetation reflectivity and shortwave surface energy exchange. We also demonstrate that much of the spatial variation in canopy N can be detected by using broad-band satellite sensors, offering a means through which these findings can be applied toward improved application of coupled carbon cycle--climate models. nitrogen cycle | climate change | foliar nitrogen | ecosystem-climate feedback | remote sensing

A QM/MM method was applied, which made use of mean field approximation to study hydrogen fluoride in the liquid phase. The results permitted to conclude that this kind of method yields satisfactory results for the thermodynamics and structural properties of the liquid HF.

Although understanding of nitrogen cycling and nitrification in forest ecosystems has improved greatly over the past several decades, our ability to characterize spatial patterns is still quite limited. A number of studies have shown linkages between canopy chemistry and N cycling, but few have considered the degree to which these trends can provide an indicator of forest N status across large, heterogeneous landscapes. In this study, we examined relationships among canopy chemistry, nitrogen cycling, and soil carbon: nitrogen ratios across 30 forested stands in the White Mountains of New Hampshire. Plots included a range of species (sugar maple, red maple, American beech, yellow birch, paper birch, red spruce, balsam fir, eastern hemlock) and were broadly grouped into two disturbance categories: those that were historically affected by intensive logging and/or fire and those that experienced minimal human disturbance. Across all plots, rates of net N mineralization and net nitrification were correlated with canopy nitrogen concentrations, but the relationships differed between disturbance treatments. In deciduous forests, historically undisturbed stands had significantly higher rates of net N mineralization and net nitrification than previously disturbed stands, but these differences were not clearly reflected in patterns of stand-level canopy chemistry. Although soil C:N ratios also differed between disturbed and undisturbed stands, a relationship between soil C:N ratios and canopy lignin:N ratios did not vary with either forest type or disturbance, suggesting that this trend is more consistent across diverse conditions. Relationships between foliar chemistry and N cycling within individual species revealed interesting differences between species and functional groups. For four out of five deciduous species, foliar N increased with increasing net N mineralization, indicating that species were responsive to changes in N availability and suggesting a positive feedback between foliar chemistry and soil N status. These patterns led to significant differences in foliar N between disturbance treatments for some species, but at the stand level, these differences were masked by successional changes in species composition. Among coniferous species, foliar N showed no variation across wide N-cycling gradients, suggesting a fundamentally different plant-soil interaction. We also examined the potential for extending observed field relationships to the regional level using a high-quality data set of high spectral resolution remote sensing, obtained from NASA's AVIRIS instrument (Airborne Visible and InfraRed Imaging Spectrometer). Cloud-free AVIRIS data from 56 scenes covering the White Mountain National Forest were calibrated to canopy lignin:N ratios and were applied to prediction of C:N ratios in soils. Validation at 10 independent plots showed good prediction accuracy but suggested some overprediction at the low end of the range. Preliminary regional estimates of soil C:N ratios indicate that 63% of the region's land area falls below a value of 22. This value is significant because our field data identified this as a critical threshold for the onset of nitrification. Below C:N = 22, we expect increasing but variable rates of nitrification, depending on other factors such as disturbance or species composition. Key words: AVIRIS; canopy chemistry; C:N ratio; disturbance; foliar nitrogen; land use history; nitrification; nitrogen mineralization; plant-soil relations; regional variation; remote sensing; succession; White Mountains, New Hampshire (USA).

A study was conducted to determine the effects of postprandial free fatty acids (FFA) on corticosteroid-binding globulin (CBG) activity and serum cortisol levels. Eleven healthy female subjects 20-30 yrs. old participated in the study. The results show that saturated, monounsaturated and polyunsaturated FFAs affected the biological activity of CBG in different degrees. Furthermore, modulation of CBG activity caused a sustained increase in the level of cortisol in the blood.