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.

In nature, iron (Fe) occurs in abundance and ranks fourth among all elements on Earth’s surface. Still, its availability to plants is reduced, once this element is in the form of hydrated oxides, which can limit plant productivity and biomass production. On the other hand, in high concentrations, this essential micronutrient for the plants can become a toxic agent, increasing the environmental contamination. Fe is necessary for the maintenance of essential processes like respiration and photosynthesis, participating in the electron transport chain and in the conversion between Fe²⁺ and Fe³⁺, being a key element for carbon dioxide (CO₂) fixation and, therefore, important for crop production of cultivated or natural species. The balance of Fe should be strictly controlled, because both its deficiency and its toxicity affect the physiological process of plants. In aerated soils Fe is present in the form of Fe³⁺, which is the oxidized form and is less available to plants, so these organisms have developed different strategies for absorption, transport and storage of Fe. Deficiency and excess of Fe correlate with local soil conditions and with the care adopted in plant nutrition during the phenological phases and/or in the course of its cultivation. In situations of excessive accumulation of Fe in tissues, an enhancement of hydroxyl radical generation (OH^•) occurs by Fenton reaction. Here, we review the nutritional, genetic and ecophysiological aspects of uptake, translocation and accumulation of Fe ions in plants growing under conditions of deficiency or toxicity of this metal.

Summary: 1. Atmospheric ammonia (NH₃) is one of the main drivers for ecosystem changes world‐wide, including biodiversity loss. Modelling its deposition to evaluate its impact on ecosystems has been the focus of many studies. For that, universal indicators are needed to determine and compare the early effects of NH₃ across ecosystems.2. We evaluate the effects of atmospheric NH₃ in ecosystems using lichens, which are one of the most sensitive communities at the ecosystem level. Rather than measuring total diversity, we use a functional diversity approach because this is potentially a more universal tool.3. We evaluated the spatial and temporal patterns of atmospheric NH₃ concentrations ([NH₃]_atm) emitted from a point‐source over a 1‐year period in a cork oak Mediterranean woodland. We observed a temporal pattern of [NH₃]_atm, with maximum concentrations during autumn.4. The distribution of lichen species was c. 90% explained by [NH₃]_atm. The tolerance of lichen species to atmospheric NH₃, based on expert knowledge from literature, was tested for the first time against direct measurements of atmospheric NH₃. Most species were well classified, with the exception of Lecanora albella and Chrysothrix candelaris, which were more tolerant than expected. Our updated lichen classification can be used to establish lichen functional groups that respond to atmospheric NH₃, and these can be used in other Mediterranean countries.5. Increasing [NH₃]_atm led to a complete replacement of oligotrophic by nitrophytic species within 65 m of the NH₃ source. The geostatistical analysis of functional diversity variables yielded a spatial model with low non‐spatial variance, indicating that these variables can cope robustly with high spatial variation in NH₃.6. Synthesis and applications. Our results support the use of functional diversity variables, such as a lichen diversity value, as accurate and robust indicators of the effects of atmospheric NH₃ on ecosystems. The spatial modelling of these indicators can provide information with high spatial resolution about the effects of atmospheric NH₃ around point‐ and diffuse sources. As this methodology is based on functional groups, it can be applied to monitor both the impact of atmospheric NH₃ and the success of mitigation strategies.