Susana Elvira

A reappraisal of the use of DMSO for the extraction and determination of chlorophylls a and b in lichens and higher plants

Abstract The use of DMSO for the extraction and determination of chlorophylls a and b in lichens and higher plants was reevaluated. Because of differences between the absorption spectra of pure chlorophylls a and b in DMSO and 80% acetone, formulae to calculate the individual concentrations of chlorophyll a, chlorophyll b and total (a + b) chlorophyll in pigment extracts were redetermined for specific use with DMSO. In lichens, the problem of chlorophyll degradation resulting from the presence of acidic lichen substances was specifically addressed. Repeated washing of thalli with carbonate-saturated 100% acetone followed by extraction in DMSO containing PVPi minimized the conversion of chlorophylls to phaeophytin during extraction of chlorophylls from lichens for which the content of lichen substances was characterized. In lichens containing significant quantities of acidic compounds, the modified DMSO assay proved superior to 80% acetone for the extraction and determination of chlorophyll a and b concentrations. In a range of higher plants, determinations of chlorophyll a and b concentrations were virtually identical when the modified DMSO assay was compared with the traditional method of chlorophyll extraction using 80% acetone. Moreover, DMSO extracts could be cold-stored for up to 7 days with no significant loss of chlorophylls a or b, or changes in the a/b ratio. Potential eco-physiological applications of the modified DMSO assay, which eliminates the necessity for grinding plant material and centrifuging plant extracts, are discussed.

Reflectance assessment of summer ozone fumigated Mediterranean white pine seedlings

Abstract Seedlings of Pinus halepensis L. grown for three summers in open top chambers (OTC) in Northeastern Spain were exposed to three ozone (O3) treatments: charcoal filtered air (CA), non-filtered (NF) and non-filtered plus 40 nl 1−1 O3 (FU). Ambient air plots (AA) in open air were established to assess the chamber effect. A clear seasonal trend was found in the physiological response of these pine seedlings in summer periods, with lower needle chlorophyll concentrations, and higher absorbance ratios for wavelengths at 435 nm and 665 nm ( A435 A665 ) which is indicative of carotenoid/chlorophyll a ratio. Old needles from the FU treatment had lower chlorophyll content and higher absorbance ratios ( A435 A665 ) than those of other treatments. Spectral reflectance indices assessing green biomass (NDVI), chlorophyll concentration (‘red edge’), the carotenoid/chlorophyll ratio (SIPI), and photosynthetic efficiency (SIXI) clearly followed the same seasonal trend, but were not statistically distinguishable from those of different ozone levels. These results are attributable to the dominance by the young needles in the sensors field of view, which showed no clear biological differences with ozone treatment. Only ambient air seedlings presented different values for the reflectance indices in consonance with their lower chlorophyll content and higher carotenoid/chlorophyll ratio.

Sensitivity analysis of a parameterization of the stomatal component of the DO3SE model for Quercus ilex to estimate ozone fluxes

A sensitivity analysis of a proposed parameterization of the stomatal conductance (g(s)) module of the European ozone deposition model (DO(3)SE) for Quercus ilex was performed. The performance of the model was tested against measured g(s) in the field at three sites in Spain. The best fit of the model was found for those sites, or during those periods, facing no or mild stress conditions, but a worse performance was found under severe drought or temperature stress, mostly occurring at continental sites. The best performance was obtained when both f(phen) and f(SWP) were included. A local parameterization accounting for the lower temperatures recorded in winter and the higher water shortage at the continental sites resulted in a better performance of the model. The overall results indicate that two different parameterizations of the model are needed, one for marine-influenced sites and another one for continental sites.

Modelling the influence of peri-urban trees in the air quality of Madrid region (Spain)

Tropospheric ozone (O(3)) is considered one of the most important air pollutants affecting human health. The role of peri-urban vegetation in modifying O(3) concentrations has been analyzed in the Madrid region (Spain) using the V200603par-rc1 version of the CHIMERE air quality model. The 3.7 version of the MM5 meteorological model was used to provide meteorological input data to the CHIMERE. The emissions were derived from the EMEP database for 2003. Land use data and the stomatal conductance model included in CHIMERE were modified according to the latest information available for the study area. Two cases were considered for the period April-September 2003: (1) actual land use and (2) a fictitious scenario where El Pardo peri-urban forest was converted to bare-soil. The results show that El Pardo forest constitutes a sink of O(3) since removing this green area increased O(3) levels over the modified area and over down-wind surrounding areas.

Ecological impacts of atmospheric pollution and interactions with climate change in terrestrial ecosystems of the mediterranean basin: Current research and future directions

Mediterranean Basin ecosystems, their unique biodiversity, and the key services they provide are currently at risk due to air pollution and climate change, yet only a limited number of isolated and geographically-restricted studies have addressed this topic, often with contrasting results. Particularities of air pollution in this region include high O3 levels due to high air temperatures and solar radiation, the stability of air masses, and dominance of dry over wet nitrogen deposition. Moreover, the unique abiotic and biotic factors (e.g., climate, vegetation type, relevance of Saharan dust inputs) modulating the response of Mediterranean ecosystems at various spatiotemporal scales make it difficult to understand, and thus predict, the consequences of human activities that cause air pollution in the Mediterranean Basin. Therefore, there is an urgent need to implement coordinated research and experimental platforms along with wider environmental monitoring networks in the region. In particular, a robust deposition monitoring network in conjunction with modelling estimates is crucial, possibly including a set of common biomonitors (ideally cryptogams, an important component of the Mediterranean vegetation), to help refine pollutant deposition maps. Additionally, increased attention must be paid to functional diversity measures in future air pollution and climate change studies to establish the necessary link between biodiversity and the provision of ecosystem services in Mediterranean ecosystems. Through a coordinated effort, the Mediterranean scientific community can fill the above-mentioned gaps and reach a greater understanding of the mechanisms underlying the combined effects of air pollution and climate change in the Mediterranean Basin.

Parameterization of the stomatal component of the DO3SE model for Mediterranean evergreen broadleaf species.

An ozone (O3) deposition model (DO3SE) is currently used in Europe to define the areas where O3 concentrations lead to absorbed O3 doses that exceed the flux-based critical levels above which phytotoxic effects would be likely recorded. This mapping exercise relies mostly on the accurate estimation of O3 flux through plant stomata. However, the present parameterization of the modulation of stomatal conductance (gs) behavior by different environmental variables needs further adjustment if O3 phytotoxicity is to be assessed accurately at regional or continental scales. A new parameterization of the model is proposed for Holm oak (Quercus ilex), a tree species that has been selected as a surrogate for all Mediterranean evergreen broadleaf species. This parameterization was based on a literature review, and was calibrated and validated using experimentally measured data of gs and several atmospheric and soil parameters recorded at three sites of the Iberian Peninsula experiencing long summer drought, and very cold and dry winter air (El Pardo and Miraflores) or milder conditions (Tietar). A fairly good agreement was found between modeled and measured data (R2 = 0.64) at Tietar. However, a reasonable performance (R2 = 0.47–0.62) of the model was only achieved at the most continental sites when gs and soil moisture deficit relationships were considered. The influence of root depth on gs estimation is discussed and recommendations are made to build up separate parameterizations for continental and marine-influenced Holm oak sites in the future.

Validation of ozone response functions for annual Mediterranean pasture species using close-to-field-conditions experiments

Ozone (O3) critical levels have been established under the Long-Range Transboundary Air Pollution Convention to assess the risk of O3 effects in European vegetation. A recent review study has led to the development of O3 critical levels for annual Mediterranean pasture species using plants growing in well-watered pots at a coastal site and under low levels of competition. However, uncertainties remain in the extrapolation of the O3 sensitivity of these species under natural conditions. The response of two O3-sensitive annual Mediterranean pasture Trifolium species at the coastal site was compared with the response of the same species growing at a continental site, in natural soil and subject to water-stress and inter-specific competition, representing more closely their natural habitat. The slopes of exposure- and dose-response relationships derived for the two sites showed differences in the response to O3 between sites attributed to differences in environmental growing conditions, growing medium and the level of inter-specific competition, but the effect of the individual factors could not be assessed separately. Dose-based O3 indices partially explained differences due to environmental growing conditions between sites. The slopes showed that plants were more sensitive to O3 at the continental site, but homogeneity of slopes tests revealed that results from both experimental sites may be combined. Although more experimental data considering complex inter-specific competition situations and the effect of important interactive factors such as nitrogen would be needed, these results confirm the validity of applying the current flux-based O3 critical level under close to natural growing conditions. The AOT40-based O3 critical level derived at the coastal site was also considered a suitable risk indicator in close to natural growing conditions in the absence of soil moisture limitations on plant growth.