These data suggest that adventitial myofibroblasts contribute to the process of vascular lesion formation by proliferating, synthesizing growth factors, and possibly migrating into the neointima. Increased synthesis of alpha-smooth muscle actin observed in the adventitial cells after arterial injury may constrict the injured vessel and contribute to the process of arterial remodeling and late lumen loss after angioplasty.

Seven years of carbon dioxide flux measurements indicate that a $ 90-year-old spruce dominated forest in Maine, USA, has been sequestering 174 AE 46 g C m À2 yr À1 (mean AE 1 standard deviation, nocturnal friction velocity (u * ) threshold 40.25 m s À1 ). An analysis of monthly flux anomalies showed that above-average spring and fall temperatures were significantly correlated with greater monthly C uptake while above-average summer temperatures were correlated with decreased net C uptake. Summer months with significantly drier or wetter soils than normal were also characterized by lower rates of C uptake. Years with above-average C storage were thus typically characterized by warmer than average spring and fall temperatures and adequate summer soil moisture.Environmental and forest-atmosphere flux data recorded from a second tower surrounded by similar forest, but sufficiently distant that flux source regions ('footprints'), did not overlap significantly showed almost identical temperature and solar radiation conditions, but some differences in energy partitioning could be seen. Half-hourly as well as integrated (annual) C exchange values recorded at the separate towers were very similar, with average annual net C uptake differing between the two towers by o6%. Interannual variability in net C exchange was found to be much greater than between tower variability. Simultaneous measurements from two towers were used to estimate flux data uncertainty from a single tower. Carbon-flux model parameters derived independently from each flux tower data set were not significantly different, demonstrating that flux towers can provide a robust method for establishing C exchange model parameters.

The feedback between plant litterfall and nutrient cycling processes plays a major role in the regulation of nutrient availability and net primary production in terrestrial ecosystems. While several studies have examined site-specific feedbacks between litter chemistry and nitrogen (N) availability, little is known about the interaction between climate, litter chemistry, and N availability across different ecosystems. We assembled data from several studies spanning a wide range of vegetation, soils, and climatic regimes to examine the relationship between aboveground litter chemistry and annual net N mineralization. Net N mineralization declined strongly and non-linearly as the litter lignin:N ratio increased in forest ecosystems (r = 0.74, P< 0.01). Net N mineralization decreased linearly as litter lignin concentration increased, but the relationship was significant (r = 0.63, P< 0.01) only for tree species. Litterfall quantity, N concentration, and N content correlated poorly with net N mineralization across this range of sites (r < 0.03, P = 0.17-0.26). The relationship between the litter lignin:N ratio and net N mineralization from forest floor and mineral soil was similar. The litter lignin:N ratio explained more of the variation in net N mineralization than climatic factors over a wide range of forest age classes, suggesting that litter quality (lignin:N ratio) may exert more than a proximal control over net N mineralization by influencing soil organic matter quality throughout the soil profile independent of climate.

We conducted an inverse modeling analysis, using a variety of data streams (tower-based eddy covariance measurements of net ecosystem exchange, NEE, of CO2, chamber-based measurements of soil respiration, and ancillary ecological measurements of leaf area index, litterfall, and woody biomass increment) to estimate parameters and initial carbon (C) stocks of a simple forest C-cycle model, DALEC, using Monte Carlo procedures. Our study site is the spruce-dominated Howland Forest AmeriFlux site, in central Maine, USA. Our analysis focuses on: (1) full characterization of data uncertainties, and treatment of these uncertainties in the parameter estimation; (2) evaluation of how combinations of different data streams influence posterior parameter distributions and model uncertainties; and (3) comparison of model performance (in terms of both predicted fluxes and pool dynamics) during a 4-year calibration period (1997-2000) and a 4-year validation period ("forward run", 2001-2004). We find that woody biomass increment, and, to a lesser degree, soil respiration, measurements contribute to marked reductions in uncertainties in parameter estimates and model predictions as these provide orthogonal constraints to the tower NEE measurements. However, none of the data are effective at constraining fine root or soil C pool dynamics, suggesting that these should be targets for future measurement efforts. A key finding is that adding additional constraints not only reduces uncertainties (i.e., narrower confidence intervals) on model predictions, but at the same time also results in improved model predictions by greatly reducing bias associated with predictions during the forward run.

Soil organic matter is a major component of biogeochemical cycles and is important in maintaining soil quality. We investigated relationships between soil organic C and various soil and site properties that may influence long‐term soil C accumulation across a range of soil orders in New Zealand. We used pedon and climatic data for 167 pedons under permanent grass, and carried out regression analysis between soil C (0–200 mm) contents (t ha−1) or concentrations (g kg−1) and climatic and soil properties, namely, precipitation, temperature, and contents or concentrations of sand, silt, clay, pyrophosphate‐extractable Al (Alpy), Fe oxide, and allophane. Soil clay content or concentration explained little of the variation in soil C across all soils (R2 < 0.05) and within each soil type. Likewise, mean annual precipitation and temperature explained little variation in soil C content or concentration (R2 < 0.15 for precipitation, for temperature). Allophane content or concentration was unrelated to soil C in the soils of volcanic origin; Alpy, however, correlated strongly with both soil C content and soil C concentration across all soil types (, respectively). When all factors were combined in a multiple regression analysis, the combination of Alpy and allophane contents explained the greatest amount of variation in soil C content , whereas the combination of Alpy, Fe oxide, allophane, and clay concentrations explained the greatest amount of variation in soil C concentration Our results suggest that in New Zealand soils, chemical stabilization of organic matter is the key process controlling soil C accumulation, and that clay content relates poorly to long‐term soil organic C accumulation.

Background-Inflammation has been suggested to play a role in vascular lesion formation after angioplasty. Whereas previous studies have focused on inflammatory reactions in the intima and media, less attention has been paid to adventitial and perivascular responses and their potential role in vascular remodeling. Methods and Results-Balloon overstretch injury of porcine coronary arteries was performed with standard clinical angioplasty catheters. Vessels were examined from 0.5 hour to 14 days after injury by immunohistochemistry and in situ hybridization (ISH) for neutrophil and macrophage markers, cell adhesion molecules (P-selectin, E-selectin, and vascular cell adhesion molecule-1), and neutrophil-specific CXC chemokines (alveolar macrophage-derived neutrophil chemotactic factor [AMCF]-I/interleukin-8 and AMCF-II). Neutrophils accumulated in the adventitia surrounding the injury site from 2 hours to 3 days, followed by macrophages from 1 to 7 days after angioplasty. Inflammation was associated temporally with the expression of mRNAs encoding cell adhesion molecules and chemokines. The main inflammatory and proliferative foci were not limited to the adventitia but rather extended many millimeters away from the injured vessel throughout the surrounding adipose and myocardial tissues. Conclusions-Inflammatory

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