Continuous chlorophyll fluorescence, gas exchange and microclimate monitoring in a natural soil crust habitat in Tabernas badlands, Almería, Spain: progressing towards a model to understand productivity

The Soil Crust International project aims to better understand the functioning of biological soil crust environments (BSC) in Europe in order to understand the importance of these ecosystems. The final objective of this project is to inform and strengthen protection strategies for these types of habitats in the frame of the European Union. To achieve this, four different soil crust regions have been chosen in Europe following latitudinal and altitudinal gradients. The work presented here is based on the simultaneous monitoring of gas exchange, chlorophyll fluorescence and microclimate of the most abundant BSC in one of these four locations, the Tabernas badlands, Almeria, SE Spain, one of the driest regions in Europe. The five BSC types monitored are dominated by the lichen species Squamarina cartilaginea, Diploschistes diacapsis, Toninia albilabra and Psora decipiens and by the moss Didymodon rigidulus. We aim to understand the conditions in which the BSC are metabolically active in order to get a better knowledge about the contribution of the BSC to the carbon budget of the ecosystem. Our first results after nearly 1 year of chlorophyll fluorescence and microclimatic monitoring linked to gas exchange data during typical activity days obtained in the field suggest similar physiological performance between the different BSC types studied. BSC were active under suboptimal conditions, and activity duration was not different whether measured by chlorophyll a fluorescence or CO2 gas exchange, a relationship that will be the basis of a productivity model

Characterization of the responses to saline stress in the symbiotic green microalga Trebouxia sp. TR9

[EN] Main conclusion. For the first time we provide a study on the physiological, ultrastructural and molecular effects of salt stress on a terrestrial symbiotic green microalga, Trebouxia sp. TR9. Although tolerance to saline conditions has been thoroughly studied in plants and, to an extent, free-living microalgae, scientific data regarding salt stress on symbiotic lichen microalgae is scarce to non-existent. Since lichen phycobionts are capable of enduring harsh, restrictive and rapidly changing environments, it is interesting to study the metabolic machinery operating under these extreme conditions. We aim to determine the effects of prolonged exposure to high salt concentrations on the symbiotic phycobiont Trebouxia sp. TR9, isolated from the lichen Ramalina farinacea. Our results suggest that, when this alga is confronted with extreme saline conditions, the cellular structures are affected to an extent, with limited chlorophyll content loss and photosynthetic activity remaining after 72h of exposure to 5M NaCl. Furthermore, this organism displays a rather different molecular response compared to land plants and free-living halophile microalgae, with no noticeable increase in ABA levels and ABA-related gene expression until the external NaCl concentration is raised to 3M NaCl. Despite this, the ABA transduction pathway seems functional, since the ABA-related genes tested are responsive to exogenous ABA. These observations could suggest that this symbiotic green alga may have developed alternative molecular pathways to cope with highly saline environments.Supported by the Ministerio de Economía y Competitividad (MINECO, Spain) and FEDER (CGL2016-79158-P), and the PROMETEO Excellence in Research Program (Generalitat Valenciana, Spain) (PROMETEO/2017/039). Funding for Ernesto Hinojosa-Vidal was also provided by MINECO (BES-2013-065511).Hinojosa-Vidal, E.; Marco, F.; Martínez-Alberola, F.; Escaray, F.; García-Breijo, F.; Reig-Armiñana, J.; Carrasco, P.... (2018). Characterization of the responses to saline stress in the symbiotic green microalga Trebouxia sp. TR9. Planta. 248(6):1473-1486. https://doi.org/10.1007/s00425-018-2993-8S147314862486Álvarez R, del Hoyo A, Díaz-Rodríguez C et al (2015) Lichen rehydration in heavy metal-polluted environments: Pb modulates the oxidative response of both Ramalina farinacea thalli and its isolated microalgae. 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