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Biocrusts are major contributors to dryland diversity, functioning, and services. However, little is known about how habitat degradation will impact multiple facets of biocrust diversity and measurable functional traits. We evaluated changes in taxonomic, functional, and phylogenetic diversity of biocrust-forming lichens along a habitat degradation gradient related to the presence of linear infrastructure (i.e., a road) and a profound agricultural driven transformation. To do so, we selected 50 remnants of a Mediterranean shrubland. We considered several surrogates of habitat quality and causal disturbance on the various diversity facets of biocrusts by using structural equation modeling, hypothesizing that habitat degradation primarily affects functional diversity, which in turn regulates changes in taxonomic and phylogenetic diversities, and also that taxonomic and phylogenetic diversities are coupled. Fragment connectivity, distance to linear infrastructure (i.e., a road) and, particularly, soil fertility (i.e., soil P concentration), had mostly negative effects on biocrust functional diversity, which in turn affected both taxonomic and phylogenetic diversities. However, we found no direct effects of habitat degradation variables on the taxonomic and phylogenetic diversities. We also found that increases in phylogenetic diversity had a positive effect on taxonomic diversity along the habitat degradation gradient. Our results indicate that functional diversity of biocrusts is strongly affected by habitat degradation, which may profoundly alter their contribution to ecosystem functioning and services. Furthermore, functional diversity regulates the response of biocrust taxonomic and phylogenetic diversity to habitat degradation. These findings indicate that habitat degradation alters and simplifies the diversity of functional traits of biocrust-forming lichens, leading to biodiversity loss, with important consequences for the conservation of global drylands biodiversity.

Understanding patterns of habitat natural recovery after human-made disturbances is critical for theconservation of ecosystems under high environmental stress, such as drylands. In particular, the unassisted estab-lishment of nonvascular plants such as biological soil crusts or biocrust communities (e.g., soil lichens, mossesand cyanobacteria) in newly formed habitats is not yet fully understood. However, the potential of biocrusts toimprove soil structure and function at the early stages of succession and promote ecosystem recovery is enor-mous. In this study, we evaluated the capacity of lichen biocrusts to spontaneously establish and develop on roadslopes in a Mediterranean shrubland. We also compared taxonomic and functional diversity of biocrusts betweenroad slopes and natural habitats in the surroundings. Biocrust richness and cover, species composition, and func-tional structure were measured in 17 road slopes (nine roadcuts and eight embankments) along a 13 km highwaystretch. Topography, soil properties and vascular plant communities of road slopes were also characterized. Weused Kruskal–Wallis tests and applied redundancy analysis (RDA) to test the effect of environmental scenario(road slopes vs. natural habitat) and other local factors on biocrust features. We found that biocrusts were com-mon in road slopes after∼20 years of construction with no human assistance needed. However, species richnessand cover were still lower than in natural remnants. Also, functional structure was quite similar between roadcuts(i.e., after soil excavation) and natural remnants, and topography and soil properties influenced species composi-tion while environmental scenario type and vascular plant cover did not. These findings further support the ideaof biocrusts as promising restoration tools in drylands and confirm the critical role of edaphic factors in biocrustestablishment and development in land-use change scenarios.

Grazing represents one of the most common disturbances in drylands worldwide, affecting both ecosystem structure and functioning. Despite the efforts to understand the nature and magnitude of grazing effects on ecosystem components and processes, contrasting results continue to arise. This is particularly remarkable for the biological soil crust (BSC) communities (i.e., cyanobacteria, lichens, and bryophytes), which play an important role in soil dynamics. Here we evaluated simultaneously the effect of grazing impact on BSC communities (resistance) and recovery after livestock exclusion (resilience) in a semiarid grassland of Central Mexico. In particular, we examined BSC species distribution, species richness, taxonomical group cover (i.e., cyanobacteria, lichen, bryophyte), and composition along a disturbance gradient with different grazing regimes (low, medium, high impact) and along a recovery gradient with differently aged livestock exclosures (short-, medium-, long-term exclusion). Differences in grazing impact and time of recovery from grazing both resulted in slight changes in species richness; however, there were pronounced shifts in species composition and group cover. We found we could distinguish four highly diverse and dynamic BSC species groups: (1) species with high resistance and resilience to grazing, (2) species with high resistance but low resilience, (3) species with low resistance but high resilience, and (4) species with low resistance and resilience. While disturbance resulted in a novel diversity configuration, which may profoundly affect ecosystem functioning, we observed that 10 years of disturbance removal did not lead to the ecosystem structure found after 27 years of recovery. These findings are an important contribution to our understanding of BCS dynamics from a species and community perspective placed in a land use change context.

Ajuts: This manuscript resulted from the 1st "Committee on Air Pollution Effects Research on Mediterranean Ecosystems" (CAPERmed) Conference celebrated in Lisbon, 2014 (http://capermed.weebly.com/). All attendants to this conference are, therefore, greatly acknowledged. Fundação para a Ciência e Tecnologia (FCT) is acknowledged through the Post Doc grant SFRH/BPD/85419/2012 to Teresa Dias and the Investigador grant to Silvana Munzi. ADM, EP and PS thank the LIFE10 ENV/FR/208 project MOTTLES. EP thanks also the Fondazione Cassa di Risparmio di Firenze (2013/7956). ROH is supported by a Juan de la Cierva Fellowship (IJCI-2014-21252) of the Spanish Ministry of Economy and Competitiveness. The authors declare no conflicts of interest. 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.

Concostrina-Zubiri, L., Martinez, I., Huber-Sannwald, E., Escudero, A. 2013. Biological Soil Crust effects and responses in arid ecosystems: recent advances at the species level. Ecosistemas 22(3):95-000. Doi.: 10.7818/ECOS.2013.22-3.13. Biological soil crusts (BSCs) constitute a complex component of the ecosystem formed by different organisms (lichens, mosses, liverworts, cyanobacteria, fungi, algae) associated with soil surface. These communities are present in a wide variety of ecosystems; however, their abundance is generally higher in arid environments with sparse vegetation cover. In these ecosystems, BSCs greatly contribute to biodiversity and ecosystem functioning. Due to technical difficulties in species identification, most studies on BSCs have been carried out at community and morphotype levels. These studies have emphasized the potential role of BSCs in defining ecosystem structure and functioning by: interacting with topsoil layers and other soil organisms, participating in carbon and nitrogen fixation, and also in hydrological and nutrient cycling. Notwithstanding, recent advances in our knowledge about BSCs show substantial and interesting differences in the ecology and functional roles of BSC species, with marked implications in the management and conservation of these communities and their ecosystems. Particularly, it has been observed that BSC presence, abundance and frequency respond differently to diverse environmental factors (climatic variables, soil type, presence of vascular plants, and grazing disturbance - natural recovery) at the species level, and also do BSC effects on topsoil properties.

La costra biológica del suelo (CBS) (cianobacterias, líquenes y briófitos) es un elemento clave en los ecosistemas de zonas áridas. La costra biológica del suelo mejora la estabilidad y la fertilidad del suelo, e influye en los procesos hidrológicos. El uso de suelo inadecuado, como pastoreo de ganado intenso puede alterar severamente la composición, cobertura y función de la CBS con una retroalimentación potencial negativa en los procesos del ecosistema. Por otra parte, es limitado el conocimiento sobre (Se conoce poco en general sobre) el grado hasta el cual pueden ser afectadas las comunidades de CBS debido a pastoreo de larga duración y su capacidad de recuperación tras la eliminación del pastoreo. Considerando el importante papel que la CBS tiene en los ecosistemas áridos y la degradación severa asociada con el pastoreo, el objetivo de esta investigación es examinar las comunidades de CBS bajo diferentes regimenes de pastoreo (gradiente de perturbación) y su recuperación potencial (gradiente de recuperación) con la eliminación del ganado en corto, mediano y largo plazo en los ecosistemas de pastizal del centro de México. En este contexto, enunciamos dos preguntas centrales. 1) ¿Cómo varía la riqueza de especies, la composición de la comunidad, la densidad de especies y la cobertura de la CBS a lo largo de i) un gradiente de perturbación con diferentes regimenes de pastoreo (moderado continuo (MCG, por sus siglas en inglés), intenso estacional (HSG) e intenso continuo (HCG)) y ii) un gradiente de recuperación del pastoreo con exclusiones de ganado de distinta antigüedad (exclusiones de corto plazo con 6 años de antigüedad (SGE, por sus siglas en inglés), de mediano plazo (MGE) con 11 años, y de largo plazo (LGE) con 27 años), considerando un ciclo intra-anual de estación seca y lluviosa? 2) ¿Distintas especies o taxones de CBS responden o afectan las características del suelo en pastizales afectados por pastoreo moderado continuo (MCG), intenso estacional (HSG) o intenso continuo (HCG) respecto a un pastizal con exclusión de ganado de largo plazo?

Despite their extent and socio-ecological importance, a comprehensive biogeographical synthesis of drylands is lacking. Here we synthesize the biogeography of key organisms (vascular and nonvascular vegetation and soil microorganisms), attributes (functional traits, spatial patterns, plant–plant and plant–soil interactions) and processes (productivity and land cover) across global drylands. These areas have a long evolutionary history, are centers of diversification for many plant lineages and include important plant diversity hotspots. This diversity captures a strikingly high portion of the variation in leaf functional diversity observed globally. Part of this functional diversity is associated with the large variation in response and effect traits in the shrubs encroaching dryland grasslands. Aridity and its interplay with the traits of interacting plant species largely shape biogeographical patterns in plant–plant and plant–soil interactions, and in plant spatial patterns. Aridity also drives the composition of biocrust communities and vegetation productivity, which shows large geographical variation. We finish our review by discussing major research gaps, which include: studying regular vegetation spatial patterns; establishing large-scale plant and biocrust field surveys assessing individual-level trait measurements; knowing whether the impacts of plant–plant and plant–soil interactions on biodiversity are predictable; and assessing how elevated CO2 modulates future aridity conditions and plant productivity., This review was done thanks to the support of the European Research Council (ERC grant agreement 647038 (BIODESERT)) and Generalitat Valenciana (CIDEGENT/2018/041). MB was supported by a Juan de la Cierva Fellowship from the Spanish Ministry of Science and Innovation (FJCI-2018-036520-I). LC-Z was supported by the Marie Sklodowska-Curie Actions (grant agreement 795380 (INDECRUST)) under the European Community’s H2020-EU.1.3.2 Programme. YLB-P was supported by a Marie Sklodowska-Curie Actions Individual Fellowship (MSCA-IF) within the European Program Horizon 2020 (grant agreement 656035 (DRYFUN)). SS was supported by the Ramón y Cajal program from the Ministry of Science and Innovation (RYC-2016-20604). MD-B was supported by the Ramón y Cajal program from the Spanish Ministry of Science and Innovation (RYC2018-025483-I), and by the British Ecological Society grant agreement no. LRB17\1019 (MUSGONET). RO-H was supported by the Ramón y Cajal program from the Spanish Ministry of Science and Innovation (RYC-2017 22032).

(1) Biocrusts are key drivers of ecosystem functioning in drylands, yet our understanding of how climate change will affect the chemistry of biocrust‐forming species and their impacts on carbon (C) and nitrogen (N) cycling is still very limited. (2) Using a manipulative experiment conducted with common biocrust‐forming lichens with distinct morphology and chemistry (Buellia zoharyi, Diploschistes diacapsis, Psora decipiens and Squamarina lentigera), we evaluated changes in lichen total and isotopic C and N and several soil C and N variables after 50 months of simulated warming and rainfall reduction. (3) Climate change treatments reduced δs13C and C:N ratio in B. zoharyi, and increased δ15N in S. lentigera. Lichens had species‐specific effects on soil dissolved organic N (DON), NH4+, β‐glucosidase and acid phosphatase activity regardless of climate change treatments, while these treatments changed how lichens affected several soil properties regardless of biocrust species. Changes in thallus δ13C, N and C:N drove species‐specific effects on DON, NH4+, β‐glucosidase and acid phosphatase activity. (4) Our findings indicate that warmer and drier conditions will alter the chemistry of biocrust‐forming lichens, affecting soil nutrient cycling, and emphasize their key role as modulators of climate change impacts in dryland soils. This research was funded by the European Research Council (ERC Grant Agreements 242658 [BIOCOM] and 647038 [BIODESERT] awarded to F.T.M), and by the Marie Skłodowska-Curie Actions (MSCA Grant Agreement 795380 [INDECRUST] awarded to L.C-Z.). E.V. was supported by the 2017 program for attracting and retaining talent of Comunidad de Madrid (no. 2017‐T2/ AMB‐5406). F.T.M. also acknowledges support from Generalitat Valenciana (CIDEGENT/2018/041).

Understanding patterns of habitat natural recovery after human-made disturbances is critical for the conservation of ecosystems under high environmental stress, such as drylands. In particular, the unassisted establishment of nonvascular plants such as biological soil crusts or biocrust communities (e.g., soil lichens, mosses and cyanobacteria) in newly formed habitats is not yet fully understood. However, the potential of biocrusts to improve soil structure and function at the early stages of succession and promote ecosystem recovery is enormous. In this study, we evaluated the capacity of lichen biocrusts to spontaneously establish and develop on road slopes in a Mediterranean shrubland. We also compared taxonomic and functional diversity of biocrusts between road slopes and natural habitats in the surroundings. Biocrust richness and cover, species composition, and functional structure were measured in 17 road slopes (nine roadcuts and eight embankments) along a 13 km highway stretch. Topography, soil properties and vascular plant communities of road slopes were also characterized. We used Kruskal–Wallis tests and applied redundancy analysis (RDA) to test the effect of environmental scenario (road slopes vs. natural habitat) and other local factors on biocrust features. We found that biocrusts were common in road slopes after ∼20 years of construction with no human assistance needed. However, species richness and cover were still lower than in natural remnants. Also, functional structure was quite similar between roadcuts (i.e., after soil excavation) and natural remnants, and topography and soil properties influenced species composition while environmental scenario type and vascular plant cover did not. These findings further support the idea of biocrusts as promising restoration tools in drylands and confirm the critical role of edaphic factors in biocrust establishment and development in land-use change scenarios.

Background and aims Biocrusts are major contributors to dryland nutrient cycling by regulating C, N and P inputs and fluxes. However, our understanding about how the decomposition of biocrust constituents contributes to soil nutrient cycling in drylands is virtually unknown. Methods We conducted a microcosm experiment to: i) evaluate the litter decomposition dynamics of two common biocrust-forming species with contrasting tissue chemistry and growth form (the lichen Cladonia foliacea and the moss Syntrichia caninervis), and ii) their effects on several soil variables related to soil functioning. Results Cladonia litter decomposed gradually with time (92% total mass loss after 342 days), while Syntrichia litter decomposed much faster (92% total mass loss after 62 days, with no further losses until the end of the experiment at 342 days). We observed species-specific effects of their litter on dissolved organic N (DON) and NH4+ depending on collection time, which changed the effects of litter decomposition on DON and pH regardless of the biocrust species considered. Overall, biocrust litter had a positive effect on SOC, DON, NH+4 and acid phosphatase activity. Conclusions Our experimental results show that decomposition of biocrust tissues plays an important role in soil nutrient cycling, indicating that this process impacts the fertility and functioning of dryland soils. This research was funded by the Marie Skłodowska-Curie Actions (MSCA Grant Agreement 795380 [INDECRUST] awarded to LCZ). FTM acknowledges support from the European Research Council (ERC Grant Agreement 647038 [BIODESERT]) and Generalitat Valenciana (CIDEGENT/2018/041). EV was supported by the 2017 program for attracting and retaining talent of Comunidad de Madrid (2017-T2/ AMB-5406).

Biocrusts are key drivers of ecosystem functioning in drylands, yet our understanding of how climate change will affect the chemistry of biocrust-forming species and their impacts on carbon (C) and nitrogen (N) cycling is still very limited.Using a manipulative experiment conducted with common biocrust-forming lichens with distinct morphology and chemistry (Buellia zoharyi, Diploschistes diacapsis, Psora decipiens and Squamarina lentigera), we evaluated changes in lichen total and isotopic C and N and several soil C and N variables after 50 months of simulated warming and rainfall reduction.Climate change treatments reduced δ13C and C:N ratio in B. zoharyi, and increased δ15N in S. lentigera. Lichens had species-specific effects on soil dissolved organic N (DON), , β-glucosidase and acid phosphatase activity regardless of climate change treatments, while these treatments changed how lichens affected several soil properties regardless of biocrust species. Changes in thallus δ13C, N and C:N drove species-specific effects on DON, , β-glucosidase and acid phosphatase activity.Our findings indicate that warmer and drier conditions will alter the chemistry of biocrust-forming lichens, affecting soil nutrient cycling, and emphasize their key role as modulators of climate change impacts in dryland soils.