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This chapter reports the findings of a Working Group on how atmospheric nitrogen (N) deposition affects both terrestrial and freshwater biodiversity. Regional and global scale impacts on biodiversity are addressed, together with potential indicators. Key conclusions are that: the rates of loss in biodiversity are greatest at the lowest and initial stages of N deposition increase; changes in species compositions are related to the relative amounts of N, carbon (C) and phosphorus (P) in the plant soil system; enhanced N inputs have implications for C cycling; N deposition is known to be having adverse effects on European and North American vegetation composition; very little is known about tropical ecosystem responses, while tropical ecosystems are major biodiversity hotspots and are increasingly recipients of very high N deposition rates; N deposition alters forest fungi and mycorrhyzal relations with plants; the rapid response of forest fungi and arthropods makes them good indicators of change; predictive tools (models) that address ecosystem scale processes are necessary to address complex drivers and responses, including the integration of N deposition, climate change and land use effects; criteria can be identified for projecting sensitivity of terrestrial and aquatic ecosystems to N deposition. Future research and policy-relevant recommendations are identified.

Nitrogen (N) deposition is a major threat to the semiarid Mediterranean ecosystems. We simulated a gradient of N deposition (0, 10, 20 and 50 kg N ha−1 year−1 + 6.4 kg N ha−1 year−1 ambient deposition) in a Mediterranean shrubland from central Spain. In autumn 2011 (after 4 years of experimental duration), soil cores were taken to extract the soil fauna. Acari (45.54%) and Collembola (44.00%) were the most represented taxonomical groups, and their abundance was negatively related to soil pH. Simulated N deposition had an impact on the total number of individuals in soil as well as on Collembola and Pauropoda abundance. Collembola abundance increased with N loads up to 20 kg N ha-1 year-1 and then decreased. This response was attributed to soil acidification (between 0 and 20 kg N ha-1 year-1) and increased soil ammonium (between 20 and 50 kg N ha-1 year-1). Pauropoda were favoured by additions of 50 kg N ha-1 year-1, and it was the only taxonomical group whose abundance was exclusively related to N deposition, suggesting their potential as bioindicators. Contrary to predictions, there was a negative relationship between soil faunal abundance and plant diversity. In conclusion, soil faunal communities from semiarid Mediterranean ecosystems in central Spain seem to be primarily influenced by soil chemistry (mainly pH) but are also susceptible to increased N deposition. The main drivers of change under increased N deposition scenarios seem to be soil acidification and increased ammonium in soils where nitrate is the dominant mineral N form.

Nitrogen (N) deposition has doubled the natural N inputs received by ecosystems through biological N fixation and is currently a global problem that is affecting the Mediterranean regions. We evaluated the existing relationships between increased atmospheric N deposition and biogeochemical indicators related to soil chemical factors and cryptogam species across semiarid central, southern, and eastern Spain. The cryptogam species studied were the biocrust-forming species Pleurochaete squarrosa (moss) and Cladonia foliacea (lichen). Sampling sites were chosen in Quercus coccifera (kermes oak) shrublands and Pinus halepensis (Aleppo pine) forests to cover a range of inorganic N deposition representative of the levels found in the Iberian Peninsula (between 4.4 and 8.1 kg N ha(-1) year(-1)). We extended the ambient N deposition gradient by including experimental plots to which N had been added for 3 years at rates of 10, 20, and 50 kg N ha(-1) year(-1). Overall, N deposition (extant plus simulated) increased soil inorganic N availability and caused soil acidification. Nitrogen deposition increased phosphomonoesterase (PME) enzyme activity and PME/nitrate reductase (NR) ratio in both species, whereas the NR activity was reduced only in the moss. Responses of PME and NR activities were attributed to an induced N to phosphorus imbalance and to N saturation, respectively. When only considering the ambient N deposition, soil organic C and N contents were positively related to N deposition, a response driven by pine forests. The PME/NR ratios of the moss were better predictors of N deposition rates than PME or NR activities alone in shrublands, whereas no correlation between N deposition and the lichen physiology was observed. We conclude that integrative physiological measurements, such as PME/NR ratios, measured on sensitive species such as P. squarrosa, can provide useful data for national-scale biomonitoring programs, whereas soil acidification and soil C and N storage co

Anthropogenic N deposition poses a threat to European Mediterranean ecosystems. We combined data from an extant N deposition gradient (4.3–7.3 kg N ha−1 yr−1) from semiarid areas of Spain and a field experiment in central Spain to evaluate N deposition effects on soil fertility, function and cyanobacteria community. Soil organic N did not increase along the extant gradient. Nitrogen fixation decreased along existing and experimental N deposition gradients, a result possibly related to compositional shifts in soil cyanobacteria community. Net ammonification and nitrification (which dominated N-mineralization) were reduced and increased, respectively, by N fertilization, suggesting alterations in the N cycle. Soil organic C content, C:N ratios and the activity of β-glucosidase decreased along the extant gradient in most locations. Our results suggest that semiarid soils in low-productivity sites are unable to store additional N inputs, and that are also unable to mitigate increasing C emissions when experiencing increased N deposition.

N deposition is currently affecting nutrient cycling in terrestrial ecosystems. We studied the effects of four years of N application (0, 10, 20 and 50 kg N ha− 1 year− 1 + background deposition) on soil chemistry and fertility in a semiarid shrubland in central Spain. Soil pH and nutrient availability fluctuated seasonally. The inorganic-N fraction in soil was dominated by nitrate, as expected in calcareous soils. N application increased inorganic N availability in soil. There was a negative correlation between N application and soil K+ availability and pH, measured as the % change after four years. Soil N and C storage (evaluated as the % change) slightly increased after four years. Our data suggest that, in the short-term, the seasonality of nutrients overwhelm any chemical alteration related to N deposition. However, the potential implication of continuous N addition on soil chemistry in the long-term is not well understood.

Background In the Peruvian Coastal Desert, an archipelago of fog oases, locally called lomas, are centers of biodiversity and of past human activity. Fog interception by a tree canopy, dominated by the legume tree tara (Caesalpinia spinosa), enables the occurrence in the Atiquipa lomas (southern Peru) of an environmental island with a diverse flora and high productivity. Although this forest provides essential services to the local population, it has suffered 90% anthropogenic reduction in area. Restoration efforts are now getting under way, including discussion as to the most appropriate reference ecosystem to use. Methodology/Principal Findings Genetic diversity of tara was studied in the Atiquipa population and over a wide geographical and ecological range. Neither exclusive plastid haplotypes to loma formations nor clear geographical structuring of the genetic diversity was found. Photosynthetic performance and growth of seedlings naturally recruited in remnant patches of loma forest were compared with those of seedlings recruited or planted in the adjacent deforested area. Despite the greater water and nitrogen availability under tree canopy, growth of forest seedlings did not differ from that of those recruited into the deforested area, and was lower than that of planted seedlings. Tara seedlings exhibited tight stomatal control of photosynthesis, and a structural photoprotection by leaflet closure. These drought-avoiding mechanisms did not optimize seedling performance under the conditions produced by forest interception of fog moisture. Conclusions/Significance Both weak geographic partitioning of genetic variation and lack of physiological specialization of seedlings to the forest water regime strongly suggest that tara was introduced to lomas by humans. Therefore, the most diverse fragment of lomas is the result of landscape management and resource use by pre-Columbian cultures. We argue that an appropriate reference ecosystem for ecological restoration of

We review the ecological consequences of N deposition on the five Mediterranean regions of the world. Seasonality of precipitation and fires regulate the N cycle in these water-limited ecosystems, where dry N deposition dominates. Nitrogen accumulation in soils and on plant surfaces results in peaks of availability with the first winter rains. Decoupling between N flushes and plant demand promotes losses via leaching and gas emissions. Differences in P availability may control the response to N inputs and susceptibility to exotic plant invasion. Invasive grasses accumulate as fuel during the dry season, altering fire regimes. California and the Mediterranean Basin are the most threatened by N deposition; however, there is limited evidence for N deposition impacts outside of California. Consequently, more research is needed to determine critical loads for each region and vegetation type based on the most sensitive elements, such as changes in lichen species composition and N cycling.

[ES] Los estreses abióticos afectan negativamente al rendimiento de las leguminosas principalmente en suelos pobres en nitrógeno. Esto se debe a que la simbiosis Rhizobium-leguminosa y la fijación simbiótica de nitrógeno son altamente sensibles a dichos estreses. Es posible utilizar diferentes estrategias para dotar a las leguminosas de una mayor tolerancia a los estreses abióticos. Una de ellas es su transformación con genes codificadores de enzimas que acentúan la acumulación de osmolitos, lo que en algunos casos ha permitido aumentar la tolerancia de las plantas a estreses salino o hídrico. Otra es la de transformar plantas o rizobios para mejorar sus sistemas de defensa contra las especies reactivas de oxígeno, lo que también ha permitido aumentar su resistencia a los estreses ambientales y retrasar la senescencia de los nódulos. El estudio del papel de los factores de transcripción en las respuestas de las plantas a diversos estreses está adquiriendo gran importancia, por lo que su manipulación para la obtención de leguminosas tolerantes a estreses abióticos puede ser una estrategia de gran relevancia en un futuro próximo., [EN] Abiotic stresses adversely affect legume yield, mostly in nitrogen-deficient soils, as Rhizobium-legume symbioses and symbiotic nitrogen fixation are extremely sensitive to such stresses. Several strategies are being used to increase stress tolerance in legumes, such as transformation with genes coding for enzymes that enhance osmolyte accumulation, which in some cases has led to increased tolerance of plants to salt or water stress. Transformation of plants or rhizobia to improve their reactive oxygen species-quenching systems has also been shown to increase their resistance to environmental stresses and to delay nodule senescence. Currently, researchers are giving importance to the role of transcription factors in the responses of plants to various stresses and their manipulation may be an important strategy for obtaining legumes with increased tolerance to abiotic stresses in the coming future.

The aimof this work is to describe the diversity and phylogeny of rhizobial bacteria associated to nodules of Ononis tridentata L. in different geographical regions of Spain. Twenty-two bacterial isolates were characterized using several molecular techniques (16S amplified ribosomal deoxyribonucleic acid restriction analysis, fingerprinting, and sequencing) and phylogenies were inferred from their 16S and nodC gene sequences. Phylogenetically, the isolates grouped with the genera Rhizobium, Mesorhizobium, Phylobacterium, and Bosea. The nodC gene, essential for nodulation, was detected for the first time in isolates close to the genera Bosea and Phyllobacterium. The bacteria isolated showed a high diversity at the genus, species, and strain level regardless of the geographical origin of the host plant. This is the first report describing bacteria associated to nodules of O. tridentata. This shrub legume is highly prized for the revegetation of gypsum soils in semiarid Mediterranean areas. Our molecular description of bacteria associated to this legume improves the current understanding of the ecology of this plant species. Our findings have implications

Stipa tenacissima L., a perennial tussock grass widely found in semi-arid environments of the Iberian Peninsula and North Africa, is subjected to multiple stresses during the extreme summer conditions of south-east Spain. We characterised the photoprotective mechanisms of S. tenacissima during the transition from spring to summer and autumn. S. tenacissima experienced a marked water deficit ( pd < −8.4 MPa) and the complete suppression of CO2 assimilation in August, associated with a 72% reduction of maximal photochemical efficiency of PSII (Fv/Fm). These reduced Fv/Fm values were related to the pre-dawn maintenance of high levels of epoxidized forms of xanthophyll-cycle pigments (DPSpd, ca. 42% higher than spring values), and with a 60% reduction in the concentration of total chlorophyll (Chl a + b). These changes were associated with a low capacity of dissipation of the excitation energy non-radiatively (measured as NPQ). Leaves showed a complete recovery of Fv/Fm and xanthophyll and chlorophyll concentrations after the autumn rainfall, which reached levels similar to that of spring. This poikilohydric-type response of S. tenacissima to stress allows for a greater tolerance of water shortage, high temperature and high light intensity, which are typical in these semi-arid environments and accounts for its distinctive opportunistic growth.

1 Quercus coccifera, a slow-growing, evergreen oak, grows in contrasting environments in the Mediterranean Basin. Habitat-based selection may have promoted divergence between populations with respect to phenotypic plasticity and genetic variability. 2 We tested the hypothesis that populations of the Q. coccifera originating from a rock outcrop, a continental garrigue formation and an oceanic forest would differ in their plastic response to light intensity. Plants from these populations were grown from acorns in a common garden at 100% and 20% full sunlight. Light response analysis was based on photochemical efficiency, xanthophyll pool, nutrient allocation, growth, crown architecture and light absorption. 3 Light-responsive characters ranged from the subcellular to the whole-plant level. The greatest divergences between sun and shade phenotypes were observed in leaf size, leaf angle and leaf area ratio. However, plasticity in these traits depended on plant provenance. 4 Regardless of the level of organization, populations were invariably ranked in the same order of plasticity when averaged over light-responsive features, with plants originating from the rock outcrop showing the least plasticity and those from the forest the largest. The forest population also had the greatest genetic variability with respect to the isoperoxidase polymorphism. 5 Among populations, plants originating from the phosphorus-deficient rock outcrop contained 30% more P per unit dry weight. Plants from the forest population had 5% more photoprotective xanthophylls, 30% larger total leaf area, with less lobed and larger leaves and a differential plasticity in leaf azimuth. 6 Differences among populations suggested ecotypic differentiation towards less phenotypic plasticity in the most homogeneous light environments. The ecological breadth of the species seemed to be derived not only from its tolerance of Mediterranean conditions but also from the specialization of its populations in contrasti

We have explored leaf-level plastic response to light and nutrients of Quercus ilex and Q. coccifera, two closely related Mediterranean evergreen sclerophylls, in a factorial experiment with seedlings. Leaf phenotypic plasticity, assessed by a relative index (PI =(maximum value - minimum)}maximum) in combination with the significance of the difference among means, was studied in 37 morphological and physiological variables. Light had significant effects on most variables relating to photosynthetic pigments, chlorophyll fluorescence and gas exchange, whereas nutrient treatment had a signi®cant effect in only 10% of the variables. Chlorophyll content was higher in the shade whereas carotenoid content and nonphotochemical quenching increased with light. Nutrient limitations increased the xanthophyll-cycle pool but only at high light intensities, and the same interaction between light and nutrients was observed for lutein. Predawn photochemical efficiency of PSII was not affected by either light or nutrients, although midday photochemical efficiency of PSII was lower at high light intensities. Photosynthetic light compensation point and dark respiration on an area basis decreased with light, but photosynthetic capacity on a dry mass basis and photochemical quenching were higher in low light, which translated into a higher nitrogen use efficiency in the shade. We expected Q. ilex, the species of the widest ecological distribution, to be more plastic than Q. coccifera, but differences were minor: Q. ilex exhibited a significant response to light in 13% more of the variables than Q. coccifera, but mean PI was very similar in the two species. Both species tolerated full sunlight and moderate shade, but exhibited a reduced capacity to enhance photosynthetic utilization of high irradiance. When compared with evergreen shrubs from the tropical rainforest, leaf responsiveness of the two evergreen oaks was low. We suggest that the low leaf-level responsiveness found here is part

The interactive effects of SO2 and NO1 on the green-algal lichen Ramalina farinacea (L.) Ach. were investigated using the degree of chlorophyll phaecophytinization and ultrastructural damage to the Trebouxia photobiont. Thalli were submitted to several factorial design experiments in which they were exposed to mean SO2 concentrations rauging from 118 to 140 mmol mol-1 plus or minus aqueous solutions of NO3- at either 50 or 1000 umol.L-1, for 6-14 days.

Diurnal changes in chlorophyll fluorescence and carotenoid composition were studied in artificially hydrated thalli of the lichen Anaptychia ciliaris to assess the concomitant variations in photosynthetic efficiency and xanthophyll cycle associated energy dissipation under contrasting light conditions. One group of thalli was kept dry and hydrated only 15 minutes before each measurement. Half of the thalli of each group were kept in the shade (natural environment) while the other half were exposed to direct sunlight. The photochemical efficiency of photosystem II (assessed by the fluorescence parameter Fv/Fm) decreased significantly towards the end of the day in thalli of A. ciliaris kept wet under direct sunlight, but not in wet, sheded thalli. The relative proportions of antheraxanthin (A) and zeaxanthin (Z) of wet thalli exposed to direct sunlight showed a significant increase in the afternoon and a sharp decrease during the evening. Dry thalli hydrated just 15 minutes before the measurements showed similar diurnal changes in Fv/Fm and in the relative proportions of A + Z to the continuously wet thalli under the same light environment. Predawn data from naturally dried thalli indicated a sustained high proportion of A + Z that accounted for a relatively low photochemical efficiency at the beginning of the experiments.