Tortajada-Genaro L.-A.,Polytechnic University of Valencia |
Borras E.,Fundacion CEAM
Journal of Environmental Monitoring | Year: 2011
The tapered element oscillating microbalance (TEOM) system is widely used to measure continuous particle mass concentrations in air quality networks. However, the semi-volatile aerosol material is lost under normal operation conditions (50 °C). This study has evaluated the error in the organic fraction of the TEOM-measured secondary organic aerosols formed from the degradation of biogenic pollutants. Experiments were carried out under controlled, water-free conditions in a fully equipped, high volume atmospheric simulator - the European PhotoReactor (EUPHORE). The ozonolysis of α-pinene, β-pinene and limonene provided a reproducible source of organic aerosol. Particulate matter concentration profiles were registered for different TEOM operating temperatures. When these values were compared with values from a filter-based gravimetric method and a scanning mobility particle sizer (SMPS), they showed that the differences between monitoring systems increased with increasing TEOM temperature. According to our results, when the TEOM is operated at 50 °C, it fails to measure 32-46% of the organic particulate material, depending on the aerosol precursor. This study has also identified and quantified the multi-oxygenated organic compounds lost in the TEOM monitoring by using a method based on the gas chromatography-mass spectrometry technique. Important losses have been calculated for relevant ambient aerosol compounds such as pinonic acid, pinonaldehyde, norpinone and limonalic acid. In conclusion, the present study has demonstrated that a high operating temperature of the TEOM monitor reduces the humidity interference but underestimates the semi-volatile organic fraction. © The Royal Society of Chemistry.
Pausas J.G.,CIDE CSIC |
Ribeiro E.,Fundacion CEAM
Global Ecology and Biogeography | Year: 2013
Aim: It has been suggested that on a global scale, fire activity changes along the productivity/aridity gradient following a humped relationship, i.e. the intermediate fire-productivity hypothesis. This relation should be driven by differing relative roles of the main fire drivers (weather and fuel) along the productivity gradient. However, the full intermediate fire-productivity model across all world ecosystems remains to be validated. Location: The entire globe, excluding Antarctica. Methods: To test the intermediate fire-productivity hypothesis, we use the world ecoregions as a spatial unit and, for each ecoregion, we compiled remotely sensed fire activity, climate, biomass and productivity information. The regression coefficient between monthly MODIS fire activity and monthly maximum temperature in each ecoregion was considered an indicator of the sensitivity of fire to high temperatures in the ecoregion. We used linear and generalized additive models to test for the linear and humped relationships. Results: Fire occurs in most ecoregions. Fire activity peaked in tropical grasslands and savannas, and significantly decreased towards the extremes of the productivity gradient. Both the sensitivity of fire to high temperatures and above-ground biomass increased monotonically with productivity. In other words, fire activity in low-productivity ecosystems is not driven by warm periods and is limited by low biomass; in contrast, in high-productivity ecosystems fire is more sensitive to high temperatures, and in these ecosystems, the available biomass for fires is high. Main conclusion: The results support the intermediate fire-productivity model on a global scale and suggest that climatic warming may affect fire activity differently depending on the productivity of the region. Fire regimes in productive regions are vulnerable to warming (drought-driven fire regime changes), while in low-productivity regions fire activity is more vulnerable to fuel changes (fuel-driven fire regime changes). © 2012 John Wiley & Sons Ltd.
Kaye J.P.,Pennsylvania State University |
Romanya J.,University of Barcelona |
Vallejo V.R.,Fundacion CEAM
Oecologia | Year: 2010
We measured plant and soil carbon (C) storage following canopy-replacing wildfires in woodlands of northeastern Spain that include an understory of shrubs dominated by Quercus coccifera and an overstory of Pinus halepensis trees. Established plant succession models predict rapid shrub recovery in these ecosystems, and we build on this model by contrasting shrub succession with long-term C storage in soils, trees, and the whole ecosystem. We used chronosequence and repeated sampling approaches to detect change over time. Aboveground plant C increased from <100 to ~3,000 g C m-2 over 30 years following fire, which is substantially less than the 5,942 ± 487 g C m-2 (mean ±1 standard error) in unburned sites. As expected, shrubs accumulated C rapidly, but the capacity for C storage in shrubs was <600 g C m-2. Pines were the largest plant C pool in sites >20 years post fire, and accounted for all of the difference in plant C between older burned sites and unburned sites. In contrast, soil C was initially higher in burned sites (~4,500 g C m-2) than in unburned sites (3,264 ± 261 g C m-2) but burned site C declined to unburned levels within 10 years after fire. Combining these results with prior research suggests two states for C storage. When pine regeneration is successful, ~9,200 g C m-2 accumulate in woodlands but when tree regeneration fails (due to microclimatic stress or short fire return intervals), ecosystem C storage of ~4,000 g C m-2 will occur in the resulting shrublands. © 2010 Springer-Verlag.
Alcazar R.,Max Planck Institute for Plant Breeding Research |
Altabella T.,University of Barcelona |
Marco F.,Fundacion CEAM |
Bortolotti C.,University of Barcelona |
And 4 more authors.
Planta | Year: 2010
Early studies on plant polyamine research pointed to their involvement in responses to different environmental stresses. During the last few years, genetic, transcriptomic and metabolomic approaches have unravelled key functions of different polyamines in the regulation of abiotic stress tolerance. Nevertheless, the precise molecular mechanism(s) by which polyamines control plant responses to stress stimuli are largely unknown. Recent studies indicate that polyamine signalling is involved in direct interactions with different metabolic routes and intricate hormonal cross-talks. Here we discuss the integration of polyamines with other metabolic pathways by focusing on molecular mechanisms of their action in abiotic stress tolerance. Recent advances in the cross talk between polyamines and abscisic acid are discussed and integrated with processes of reactive oxygen species (ROS) signalling, generation of nitric oxide, modulation of ion channel activities and Ca2+ homeostasis, amongst others. © Springer-Verlag 2010.
Ross I.,French National Center for Scientific Research |
Misson L.,French National Center for Scientific Research |
Rambal S.,French National Center for Scientific Research |
Arneth A.,Lund University |
And 5 more authors.
Biogeosciences | Year: 2012
Rainfall regimes became more extreme over the course of the 20th century, characterised by fewer and larger rainfall events. Such changes are expected to continue throughout the current century. The effect of changes in the temporal distribution of rainfall on ecosystem carbon fluxes is poorly understood, with most available information coming from experimental studies of grassland ecosystems. Here, continuous measurements of ecosystem carbon fluxes and precipitation from the worldwide FLUXNET network of eddy-covariance sites are exploited to investigate the effects of differences in rainfall distribution on the carbon balance of seasonally water-limited shrubland and forest sites. Once the strong dependence of ecosystem fluxes on total annual rainfall amount is accounted for, results show that sites with rainfall distributions characterised by fewer and larger rainfall events have significantly lower gross primary productivity, slightly lower ecosystem respiration and consequently a smaller net ecosystem productivity. © 2012 Author(s) CC Attribution 3.0 License.