Dual isotope analyses indicate efficient processing of atmospheric nitrate by forested watersheds in the northeastern U.S.

Author Posting. © Springer, 2008. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Biogeochemistry 90 (2008): 15-27, doi:10.1007/s10533-008-9227-2.Nitrogen from atmospheric deposition serves as the dominant source of new nitrogen to forested ecosystems in the northeastern U.S.. By combining isotopic data obtained using the denitrifier method, with chemistry and hydrology measurements we determined the relative importance of sources and control mechanisms on nitrate (NO3-) export from five forested watersheds in the Connecticut River watershed. Microbially produced NO3- was the dominant source (82-100%) of NO3- to the sampled streams as indicated by the δ15N and δ18O of NO3-. Seasonal variations in the δ18O-NO3- in streamwater are controlled by shifting hydrology and temperature affects on biotic processing, resulting in a relative increase in unprocessed NO3- export during winter months. Mass balance estimates find that the unprocessed atmospherically derived NO3- stream flux represents less than 3% of the atmospherically delivered wet NO3- flux to the region. This suggests that despite chronically elevated nitrogen deposition these forests are not nitrogen saturated and are retaining, removing, and reprocessing the vast majority of NO3- delivered to them throughout the year. These results confirm previous work within Northeastern U.S. forests and extend observations to watersheds not dominated by a snow-melt driven hydrology. In contrast to previous work, unprocessed atmospherically derived NO3- export is associated with the period of high recharge and low biotic activity as opposed to spring snowmelt and other large runoff events.This work was funded by an EPA STAR Fellowship (FP-91637501-1) and a grant from QLF/The Sound Conservancy to RTB

Site-specific differences in fatty acid composition of dendritic cells and associated adipose tissue in Popliteal Depot, Mesentery, and Omentum and their modulation by chronic inflammation and dietary lipids

Background: This study explores the role of lymphatics-associated adipocytes in determining the lipid composition of dendritic cells. Methods and Results: Adult male rats were fed plain chow, or chow supplemented with 20% sunflower or fish oil. Chronic local inflammation was induced by subcutaneous injection of 20 µg lipopolysaccharide three times a week for 2 weeks near the popliteal lymph nodes. Chemokine-stimulated dendritic cells were collected over 4 h from popliteal and mesenteric lymph nodes, and perinodal and other samples of mesenteric, popliteal and omental adipose tissue. Fatty acids extracted from triacylglycerols and/or phospholipids were separated and quantified by gas chromatography from each sample of dendritic cells and intracellular lipids, membranes, stroma and isolated adipocytes from the adipose tissue. Dendritic cells from lymph nodes and adipose tissue samples differ in fatty acid composition, and can be modulated by diet. The site-specific differences of dendritic cells correlate with those of the contiguous adipocytes. Chronic mild stimulation alters the lipid composition of dendritic cells near the inflamed site and elsewhere; changes are minimal after the fish-oil diet. The composition of adipocyte triacylglycerol and phospholipid fatty acids also changes near the stimulation site in ways that counteract alterations induced by the experimental diets. Conclusions: Fatty acids in dendritic cells differ with anatomical site, and are determined by the adjacent adipocytes, which actively regulate their own lipid composition. These findings demonstrate functional bases for the anatomical associations between adipose and lymphoid tissues and may be a mechanism by which dietary lipids modulate the immune system

“Concerning the Efficient Conversion of Epoxy Alcohols into Epoxy-Ketones Using Dioxiranes.”

Representative epoxy alcohols are cleanly converted into the corresponding epoxy ketones in high yield by selective oxidation using dimethyldioxirane (1a) and its trifluoro analogue (1b) under mild conditions. The oxidation is found to take place leaving the configuration at the epoxy functionality unaffected. The direct oxyfunctionalization of simple cyclic epoxides with the powerful dioxirane 1b provides another attractive method to access epoxy ketones regioselectively