Free-air CO enrichment (FACE) technology was used to expose a loblolly pine (Pinus taeda L.) forest to elevated atmospheric CO (ambient + 200 µl l). After 4 years, basal area of pine trees was 9.2% larger in elevated than in ambient CO plots. During the first 3 years the growth rate of pine was stimulated by ~26%. In the fourth year this stimulation declined to 23%. The average net ecosystem production (NEP) in the ambient plots was 428 gC m year, indicating that the forest was a net sink for atmospheric CO. Elevated atmospheric CO stimulated NEP by 41%. This increase was primarily an increase in plant biomass increment (57%), and secondarily increased accumulation of carbon in the forest floor (35%) and fine root increment (8%). Net primary production (NPP) was stimulated by 27%, driven primarily by increases in the growth rate of the pines. Total heterotrophic respiration (R ) increased by 165%, but total autotrophic respiration (R) was unaffected. Gross primary production was increased by 18%. The largest uncertainties in the carbon budget remain in separating belowground heterotrophic (soil microbes) and autotrophic (root) respiration. If applied to temperate forests globally, the increase in NEP that we measured would fix less than 10% of the anthropogenic CO projected to be released into the atmosphere in the year 2050. This may represent an upper limit because rising global temperatures, land disturbance, and heterotrophic decomposition of woody tissues will ultimately cause an increased flux of carbon back to the atmosphere.

The heat island effect and the high use of fossil fuels in large city centers are well documented, but by how much fossil fuel consumption is elevating atmospheric CO 2 concentrations and whether elevations in both atmospheric CO 2 and air temperature from rural to urban areas are consistently different from year to year are less well known. Our aim was to record atmospheric CO 2 concentrations, air temperature and other environmental variables in an urban area and compare it to suburban and rural sites to see if urban sites are experiencing climates expected globally in the future with climate change. A transect was established from Baltimore city center (Urban site), to the outer suburbs of Baltimore (suburban site) and out to an organic farm (rural site). At each site a weather station was set-up to monitor environmental variables for 5 years. Atmospheric CO 2 was consistently and significantly increased on average by 66 ppm from the rural to the urban site over the 5 years of the study. Air temperature was also consistently and significantly higher at the urban site (14.8 1C) compared to the suburban (13.6 1C) and rural (12.7 1C) sites. Relative humidity was not different between sites whereas the vapor pressure deficit (VPD) was significantly higher at the urban site compared to the suburban and rural sites. An increase in nitrogen deposition at the rural site of 0.6% and 1.0% compared to the suburban and urban sites was small enough not to affect soil nitrogen content. Dense urban areas with large populations and high vehicular traffic have significantly different microclimates compared to outlying suburban and rural areas. The increases in atmospheric CO 2 and air temperature are similar to changes predicted in the short term with global climate change, therefore providing an environment suitable for studying future effects of climate change on terrestrial ecosystems.

Contact with poison ivy (Toxicodendron radicans) is one of the most widely reported ailments at poison centers in the UnitedStates, and this plant has been introduced throughout the world, where it occurs with other allergenic members of the cashew family (Anacardiaceae). Approximately 80% of humans develop dermatitis upon exposure to the carbon-based active compound, urushiol. It is not known how poison ivy might respond to increasing concentrations of atmospheric carbon dioxide (CO 2), but previous work done in controlled growth chambers shows that other vines exhibit large growth enhancement from elevated CO 2. Rising CO2 is potentially responsible for the increased vine abundance that is inhibiting forest regeneration and increasing tree mortality around the world. In this 6-year study at the Duke University Free-Air CO 2 Enrichment experiment, we show that elevated atmospheric CO2 in an intact forest ecosystem increases photosynthesis, water use efficiency, growth, and population biomass of poison ivy. The CO 2 growth stimulation exceeds that of most other woody species. Furthermore, high-CO 2 plants produce a more allergenic form of urushiol. Our results indicate that Toxicodendron taxa will become more abundant and more ''toxic'' in the future, potentially affecting global forest dynamics and human health.global change ͉ forest ecology ͉ Rhus radicans

Summary• The loss of carbon below-ground through respiration of fine roots may be modified by global change. Here we tested the hypothesis that a reduction in N concentration of tree fine-roots grown in an elevated atmospheric CO 2 concentration would reduce maintenance respiration and that more energy would be used for root growth and N uptake. We partitioned total fine-root respiration ( R T ) between maintenance ( R M ), growth ( R G ), and N uptake respiration ( R N ) for loblolly pine ( Pinus taeda ) and sweetgum ( Liquidambar styraciflua ) forests exposed to elevated CO 2 .• A substantial increase in fine-root production contributed to a 151% increase in R G for loblolly pine in elevated CO 2 . Root specific R M for pine was 24% lower under elevated CO 2 but when extrapolated to the entire forest, no treatment effect could be detected.• R G (< 10%) and R N (< 3%) were small components of R M in both forests. Maintenance respiration was the vast majority of R T , and contributed 92% and 86% of these totals at the pine and sweetgum forests, respectively.• The hypothesis was rejected because the majority of fine-root respiration was used for maintenance and was not reduced by changes in root N concentration in elevated CO 2 . Because of its large contribution to R T and total soil CO 2 efflux, changes in R M caused by warming may greatly alter carbon losses from forests to the atmosphere.

We compared radiation-use efficiency of growth (epsilon;), defined as rate of biomass accumulation per unit of absorbed photosynthetically active radiation, of forest plots exposed to ambient (approximately 360 micro l l-1) or elevated (approximately 560 micro l l-1) atmospheric CO2 concentration ([CO2]). Large plots (30-m diameter) in a loblolly pine (Pinus taeda L.) plantation, which contained several hardwood species in the understory, were fumigated with a free-air CO2 enrichment system. Biomass accumulation of the dominant loblolly pines was calculated from monthly measurements of tree growth and site-specific allometric equations. Depending on the species, leaf area index (L*) was estimated by three methods: optical, allometric and litterfall. Based on the relationship between tree height and diameter during the first 3 years of exposure, we conclude that elevated [CO2] did not alter the pattern of aboveground biomass allocation in loblolly pine. There was considerable variation in L* estimates by the different methods; total L* was 18-42% lower when estimated by the optical method compared with estimates from allometric calculations, and this discrepancy was reduced when optical measurements were corrected for the non-random distribution of loblolly pine foliage. The allometric + litterfall approach revealed a seasonal maximum total L* of 6.2-7.1 with about 1/3 of the total from hardwood foliage. Elevated [CO2] had only a slight effect on L* in the first 3 years of this study. Mean epsilon; (+/- SD), calculated for loblolly pine only, was 0.49 +/- 0.05 and 0.62 +/- 0.04 g MJ-1 for trees in the ambient and elevated [CO2] plots, respectively. The 27% increase in epsilon; in response to CO2 enrichment was caused primarily by the stimulation of biomass increment, as there was only a small effect of elevated [CO2] on L* during the initial years of fumigation. Long-term increases in atmospheric [CO2] can increase epsilon; in closed-canopy forests but the absolute magnitude and duration of this increase remain uncertain.

No data are available on whether rising carbon dioxide concentration [CO 2 ] or increased air temperature can alter the establishment and persistence of common ragweed (Ambrosia artemisiifolia L.) within a plant community following soil disturbance. To determine ragweed longevity, we exposed disturbed soil with a common seed bank population to an in situ temperature and [CO 2 ] gradient along an urban-rural transect beginning in early 2002. No other consistent differences in meteorological variables (e.g. wind speed, humidity, PAR, tropospheric ozone) as a function of urbanization were documented over the course of the study (2002)(2003)(2004)(2005). Above-ground measurements of biomass over this period demonstrated that ragweed along the transect responded to urban induced increases in [CO 2 ]/temperature with peak biomass being observed at this location by the end of 2003. However, by the Fall of 2004, and continuing through 2005, urban ragweed populations had dwindled to a few plants. The temporal decline in ragweed populations was not associated with increased disease, herbivory or autoallelopathy, but was part of a demographic reduction in the total number of annual plant species observed for the urban location. In a separate experiment, we showed that such a demographic shift is consistent with CO 2 /temperature induced increases in biomass and litter accumulation, with a subsequent reduction in germination/survival of annual plant species. Overall, these data indicate that [CO 2 ]/temperature differences associated with urbanization may increase initial ragweed productivity and pollen production, but suggest that long-term, multi-year persistence of ragweed in the urban macro-environment may be dependent on other factors.

Administration of caffeine (1,3,7-trimethylxanthine), a major component of coffee, to Swiss mice at doses of 80 or 100 mg/kg body weight 60 min prior to whole-body lethal dose of gamma-irradiation (7.5 Gy) resulted in the survival of 70 and 63% of animals, respectively, at the above doses in contrast to absolutely no survivors (LD-100/25 days) in the group exposed to radiation alone. Pre-treatment with a lower concentration of caffeine (50 mg/kg) did not confer any radioprotection. The protection exerted by caffeine (80 mg/kg), however, was reduced from 70 to 50% if administered 30 min prior to irradiation. The trend statistics reveal that a dose of 80 mg/kg administered 60 min before whole-body exposure to 7.5 Gy is optimal for maximal radioprotection. However, caffeine (80 mg/kg) administered within 3 min after irradiation offered no protection. While there is documentation in the literature that caffeine is an antioxidant and radioprotector against the oxic pathway of radiation damage in a wide range of cells and organisms, this is the first report demonstrating unequivocally its potent radioprotective action in terms of survival of lethally whole-body irradiated mice.

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