Cristina Máguas

Lead (Pb) uptake and its effects on membrane integrity and chlorophyll fluorescence in different lichen species

Abstract We report an investigation into the effect on membrane integrity and chlorophyll fluorescence of extra- and intracellular lead (Pb) concentrations in lichens possessing different photosynthetic symbionts and thallus growth forms (Lobaria pulmonaria, Ramalina farinacea, Parmelia caperata and Peltigera canina). Pb uptake, particularly in cyanobiont lichens, caused a decrease in photosystem II (PSII) photochemical reactions, measured as a change in the ratio variable fluorescence:maximal fluorescence ( F v F m ). In the lichens L. pulmonaria and Parmelia caperata, the effect on PSII photochemical reactions could only be observed 48 h after Pb uptake, confirming that prolonged exposure to Pb caused an additional decrease in F v F m . We confirmed that Pb enters the cells of the lichens. We found identical maximal extracellular Pb concentrations among the different lichens; however, the maximal intracellular Pb concentrations were not identical in range. Lichen PSII photochemical reactions were more sensitive to Pb than cell membrane damage since, with increasing Pb concentrations, no clear alterations in lichen membrane permeability, as measured by the loss of intracellular K and Mg, were observed. The effects of Pb in lichens were shown to be dependent only on the nature of the photobiont. We confirmed that Pb displaced extracellular exchangeable Ca and Mg.

High competitiveness of a resource demanding invasive acacia under low resource supply

Mechanisms controlling the successful invasion of resource demanding species into low-resource environments are still poorly understood. Well-adapted native species are often considered superior competitors under stressful conditions. Here we investigate the competitive ability of the resource demanding alien Acacia longifolia, which invades nutrient-poor Mediterranean sand dunes such as in coastal areas of Portugal. We explore the hypothesis that drought may limit invasion in a factorial competition experiment of the alien invasive versus two native species of different functional groups (Halimium halimifolium, Pinus pinea), under well-watered and drought conditions. Changes in biomass, allocation pattern, and N-uptake-efficiency (via 15N-labeling) indicated a marked drought sensitivity of the invader. However, highly efficient drought adaptations of the native species did not provide a competitive advantage under water limiting conditions. The competitive strength of H.halimifolium towards the alien invader under well-watered conditions turned into a positive interaction between both species under drought. Further, low resource utilization by native species benefited A. longifolia by permitting continued high nitrogen uptake under drought. Hence, the N-fixing invader expresses low plasticity by continuous high resource utilization, even under low resource conditions. The introduction of novel traits into a community like N-fixation and high resource use may promote A. longifolia invasiveness through changes in the physical environment, i.e., the water and nutrient cycle of the invaded sand dune system, thereby potentially disrupting the co-evolved interactions within the native plant community.

Species richness of lichen functional groups in relation to land use intensity

Changing land use has a major impact on lichen diversity. This study attempts to identify patterns or trends of lichen functional groups along a land use gradient, ranging from natural forests to open agricultural landscape. In eight countries, covering six main European biogeographic regions, lichen vegetation was assessed according to a standardized scheme. Data on reproductive, vegetative and ecological traits was compiled and relative species richness for all classes of all traits calculated. Relationships between the land use gradient and relative species richness of trait classes were analysed. Open and intensively managed landscapes harbour more fertile species while sterile species are relatively more important in forests. This finding is also supported by analyses of different classes of dispersal propagules. The importance of species with the principal photobiont Trebouxia s.l. increases linearly with intensification of land use. A converse pattern is revealed by species with Trentepohlia. Concerning substratum specialization only generalists show an effect along the land use intensity gradient. Their relative species richness decreases from landscapes dominated by forests to open agricultural landscape. A considerable decline in the rare lichen species richness as a result of land intensification is predicted.

Spatial modeling of PAHs in lichens for fingerprinting of multisource atmospheric pollution.

PAHs are toxic compounds emitted by several anthropogenic sources, which have a great impact on human health. We show, for the first time, how spatial models based on PAHs intercepted by lichens can be used for fingerprinting multisource atmospheric pollution in a regional area. Urban-industrial areas showed the highest atmospheric deposition of PAHs followed by urban > industrial > agricultural > forest Multivariate analysis of lichen data showed, for the first time, a clear distinction between various sources of PAHs in the same area: urban are dominated by 4-ring PAHs, forest by 3-ring PAHs, and industrial by 5- and 6-ring PAHs or by 2-ring PAHs (petrogenic or pyrogenic, respectively). Heavy metals were also used for supporting the fingerprinting of PAH sources, reinforcing the industrial origin of 5- and 6-ring PAHs and revealing their particular nature. The spatial structure of the models for different PAHs seems to be dependent on the following factors: size and hydrophilic character of different PAHs, type of emission sources (point or nonpoint), and dispersion associated with particulates of different sizes. Based on the long-term integration of PAHs in lichens, these spatial models will significantly improve our knowledge on the impact of PAH chronic-exposure to humans and ecosystems.

Guidelines for biomonitoring persistent organic pollutants (POPs), using lichens and aquatic mosses--a review.

During the last decades, awareness regarding persistent organic pollutants (POPs), such dioxins and furans (PCDD/Fs) and polycyclic aromatic hydrocarbons (PAHs), has become a cutting-edge topic, due to their toxicity, bioaccumulation and persistency in the environment. Monitoring of PCDD/Fs and PAHs in air and water has proven to be insufficient to capture deposition and effects of these compounds in the biota. To overcome this limitation, environmental biomonitoring using lichens and aquatic mosses, have aroused as promising tools. The main aim of this work is to provide a review of: i) factors that influence the interception and accumulation of POPs by lichens; ii) how lichens and aquatic bryophytes can be used to track different pollution sources and; iii) how can these biomonitors contribute to environmental health studies. This review will allow designing a set of guidelines to be followed when using biomonitors to assess environmental POP pollution.

Stable Isotope Analysis

Abstract Reports on analytical methods for determining the geographical origin of agricultural products have been increasing since the 1980s [49] . The development of new techniques is highly desirable for consumers, agricultural farmers, retailers and administrative authorities. Various analytical techniques have been studied based on organic constituents, mineral composition, light- and heavy-element isotope ratios or combinations thereof. The analytical techniques that have been applied for the geographical origin discrimination of food may be subdivided into several groups, mainly including spectroscopic techniques and separation techniques. In general, mass spectrometry (MS) is applied to elucidate the composition of a sample by generating spectral information of the components and can be combined with other techniques. For instance, isotope ratio mass spectrometry (IRMS) is a technique that can distinguish chemically identical compounds based on their isotope content. Continuous flow IRMS (CF-IRMS) is the most common type of IRMS used in food analysis. The CF-IRMS offers online sample preparation and the possibility of interfacing with other preparation techniques, including elemental analysis, gas chromatography and high-performance liquid chromatography. In this chapter, IRMS techniques are described on the scope of food analysis, focussing on important aspects ranging from the recommended terms for the expression of stable isotope ratio measurement results to the principles and techniques of IRMS. Special consideration is given to sample preparation procedures for IRMS analysis and to the work with international stable isotope reference materials. Finally, the most recent developments and applications of this MS technique in food traceability are also addressed.

Gas exchange and carbon isotope discrimination in lichens: Evidence for interactions between CO2-concentrating mechanisms and diffusion limitation

The characteristics of gas exchange and carbon isotope discrimination were determined for a number of lichen species, representing contrasting associations between fungal (mycobiont) and photosynthetic (photobiont) organism. These parameters were evaluated with regard to the occurrence of any CO2-concentrating mechanism (CCM) expressed specifically by the green algal (phycobiont) or cyanobacterial (cyanobiont) partner. Carbon isotope discrimination (Δ) fell into three categories. The highest Δ, found in lichens comprising a phycobiont plus cyanobacteria limited to pockets in the thallus (known as cephalodia), ranged from 24 to 28‰, equivalent to a carbon isotope ratio (δ13C) of around -32 to-36‰ vs. Pee Dee Belemnite (PDB) standard. Further evidence was consistent with CO2 supply to the carboxylating system entirely mediated by diffusion rather than a CCM, in that thallus CO2 compensation point and online instantaneous Δ were also high, in the range normally associated with C3 higher plants. For lichens consisting of phycobiont or cyanobiont alone, organic material Δ formed two distinct ranges around 15‰ (equivalent to a δ13C of -23%.). Thallus compensation point and instantaneous Δ were lower in the cyanobiont group, which also showed higher maximum rates of net photosynthesis, whether expressed on the basis of thallus dry weight, chlorophyll content or area. These data provide additional evidence for the activity of a CCM in cyanobiont lichens, which only show photosynthetic activity when reactivated with liquid water. Rates of net CO2 uptake were lower in both phycobiont associations, but were relatively constant across a wide working range of thallus water contents, usually in parallel with on-line Δ. The phycobiont response was consistent whether photosynthesis had been reactivated with liquid water or water vapour. The effect of diffusion limitation could generally be seen with a 3–4‰ decrease in instantaneous Δ at the highest water contents. The expression of a CCM in phycobiont algae, although reduced compared with that in cyanobacteria, has already been related to the occurrence of pyrenoids in chloroplasts. In view of the inherent requirement of cyanobacteria for some form of CCM, and the smaller pools of dissolved inorganic carbon (DIC = CO2 + HCOinf3su−+ COinf3su2−) associated with phycobiont lichens, it appears that Δ characteristics provide a good measure of the magnitude of any CCM, albeit tempered by diffusion limitation at the highest thallus water contents.

Ammonium uptake in the nitrophytic lichen Xanthoria parietina and its effects on vitality and balance between symbionts

Ammonium uptake in the nitrophytic lichen Xanthoria parietina (L.) Th. Fr. and its effects on vitality and balance between symbionts

Community scale 15N isoscapes : tracing the spatial impact of an exotic N2-fixing invader

Plant-plant interactions are key processes shaping plant communities, but methods are lacking to accurately capture the spatial dimension of these processes. Isoscapes, i.e. spatially continuous observations of variations in stable isotope ratios, provide innovative methods to trace the spatial dimension of ecological processes at continental to global scales. Herein, we test the usefulness of nitrogen isoscapes (δ(15) N) for quantifying alterations in community functioning following exotic plant invasion. Nitrogen introduced by an exotic N(2) -fixing acacia could be accurately traced through the ecosystem and into the surrounding native vegetation by combining native species foliar δ(15) N with spatial information regarding plant location using geostatistical methods. The area impacted by N-addition was at least 3.5-fold greater than the physical area covered by the invader. Thus, downscaling isoscapes to the community level opens new frontiers in quantifying the spatial dimension of functional changes associated with invasion and in resolving the spatial component of within-community interactions.

Carbon isotope discrimination as a tracer of functional traits in a mediterranean macchia plant community

Characterising functional plant groups with simple robust parameters of structural and functional traits is an important tool in ecological research. The reliability of carbon isotope discrimination (Δ13C) as an indicator of functional types was assessed in a highly diverse mediterranean macchia comprising drought semi-deciduous malacophylls, evergreen sclerophylls and a gymnosperm. Pronounced differences in Δ13C of 4‰ occurred: semi-deciduous species (Cistus sp. L.) showed the highest and the gymnosperm (Juniperus sp. L.) the lowest Δ13C (20.3 ± 0.5‰ and 16.2 ± 0.18‰, respectively). Across all studied species, Δ13C was correlated with (i) phenology (length of growing period) and (ii) leaf structure (leaf mass and N per area). The correlation of Δ13C with leaf water potentials, an indicator of drought stress, was species-specific and only 6 out of 11 species exhibited a significant relationship. Thus, leaf phenology governs seasonal responsiveness of Δ13C to drought, which constrains its applicability as an indicator of water use efficiency, particularly in evergreen species with short growing periods. Principal components analysis indicated the robustness of Δ13C for the classification of functional groups yielding similar results based on multiple leaf traits or solely on Δ13C. Hence Δ13C provides an ecological tracer of different functional types, integrating structural, functional and phenological attributes.