Validity of Photo-oxidative stress markers and stress-related phytohormones as predictive proxies of mortality risk in the perennial herb Plantago lanceolata

Oxidative stress and hormonal regulation are hallmarks of a/biotic stress responses in plants. However, little is known about their linkage with whole-organismal mortality in long-lived species. Here, we examined the validity of photo-oxidative stress markers and stress-related phytohormones as predictive proxies of mortality risk in the perennial herb Plantago lanceolata. Capitalizing on its broad ecological niche, we examined photo-oxidative stress markers (Fv/Fm ratio, contents of chlorophylls, carotenoids, and tocochromanols, and the extent of lipid peroxidation) and stress-related phytohormones (ABA, salicylic acid and jasmonates contents) as proxies of mortality in three populations of sub-tropical and Mediterranean habitats: Virginia (VA, U.S.A.), Catalonia (CAT, Spain), and Queensland (QLD, Australia). Stress markers were measured together with the vital rates of survival, growth, and reproduction on a total of 279 individuals. Stress marker data were collected during the summer and death/survival was monitored after two and four months. Whole-organism mortality was similarly high in both sub-tropical non-native populations (ca. 30 % after a drought in VA and QLD), but lower in the native population (ca. 10 % in CAT). The contents of antioxidants (lutein, zeaxanthin, β-carotene) and the de-epoxidation state of the xanthophyll cycle (DPS) were good proxies of mortality risk in VA and QLD. DPS and all carotenoid contents per unit of chlorophyll were lower four months in advance in dead than in alive plants in VA and QLD, thus suggesting reduced photoprotective capacity increased the mortality risk in non-native populations. We show that whole-organismal mortality in P. lanceolata is associated with a reduced capacity to enhance photoprotection under abiotic stress conditions. The validity of various stress markers as predictive proxies of mortality risk is discussed

Vulnerabilidad a la sequía de la especie de alta montaña Saxifraga longifolia

[spa] Los ecosistemas de alta montaña son puntos calientes de biodiversidad, ya que proporcionan hábitats que albergan una gran variedad de especies únicas. El clima por encima del límite forestal se caracteriza por tener temperaturas extremas, elevada radiación solar y fuertes vientos, y se espera que las condiciones ambientales sean aún más duras en el marco actual del cambio climático, lo que aumentará la gravedad y la recurrencia de los eventos de sequía y pondrá en peligro a muchas especies. En este contexto, la capacidad fisiológica para responder a estas condiciones ambientales severas determinará el éxito de la supervivencia de las especies. Exploramos la influencia de la altitud y la sequía en una planta perenne, monocárpica y endémica de los Pirineos, Saxifraga longifolia, revelando adaptaciones para hacer frente al escenario de cambio climático actual de alta montaña. Evaluamos la acumulación de pigmentos, la activación de los sistemas antioxidantes y los cambios en el perfil hormonal bajo condiciones naturales y controladas. Investigamos las estrategias para hacer frente al aumento de la altitud y a las condiciones ambientales del verano alpino, con especial énfasis en las respuestas al estrés de la sequía tanto en condiciones naturales como controladas. Las condiciones de sequía activaron mecanismos de fotoprotección y antioxidantes, activando los ciclos de xantofilas (VAZ y L/Lx) y promoviendo la acumulación de antocianinas y tocoferoles. Los ajustes fisiológicos a la sequía se debieron principalmente a las acciones combinadas del ácido abscísico, el ácido salicílico y las citoquininas. Además, encontramos que la clonalidad y la latencia de las semillas pueden servir como mecanismos para prolongar la longevidad en poblaciones que se encuentran a gran altitud. Además, las plantas mostraron un endurecimiento por congelación al modificar la morfología de la hoja y la composición de la antena de captación de luz de los fotosistemas, lo que garantiza la tolerancia a la congelación durante las condiciones invernales. Concluimos que a pesar de que S. longifolia ha desarrollado mecanismos complejos que operan a nivel celular, de planta entera y poblacional para adaptarse a las duras condiciones ambientales que prevalecen actualmente en los ecosistemas de alta montaña en los Pirineos, los eventos de sequía podrían conducir a un aumento de la mortalidad dentro del marco del cambio global.[eng] High-mountain ecosystems are hotspots for biodiversity, providing habitats that shelter a great variety of unique species. Climate above the timberline is characterized by extremes in temperature, wind and solar radiation, and environmental conditions are expected to be even harsher in the current framework of climate change particularly increasing the severity and recurrence of drought events, potentially endangering many species. In this context, the physiological capacity to respond to these severe environmental conditions will determine their survival success. We explored the influence of altitude and drought in a monocarpic perennial endemic from the Pyrenees, Saxifraga longifolia, unveiling high-mountain adaptations to the current climate change scenario. We assessed pigment accumulation, activation of antioxidant systems and changes in hormonal profiling under both natural and controlled conditions. We explored the strategies to face increasing altitude and contrasting environmental conditions during the summer, with an emphasis on drought stress responses under both natural and controlled conditions. Drought conditions triggered photoprotection and antioxidant mechanisms, activating both xanthophyll (VAZ and L/Lx) cycles, and promoting anthocyanin and tocopherol accumulation. Physiological adjustments to drought were driven mainly by a cross- talk between abscisic acid, salicylic acid and cytokinins. Furthermore, we found that clonality and seed dormancy may serve as mechanisms to prolong longevity in populations occurring at high elevation. In addition, plants showed frost pre-hardening by modifying leaf morphology and photosystems light harvesting antenna composition, ensuring freezing tolerance under winter conditions. We conclude that despite S. longifolia has developed complex mechanisms that operate at the cellular, whole-plant and population levels to adapt to the harsh environmental conditions currently prevailing in high-mountain ecosystems in the Pyrenees, drought events could lead to an increased mortality in the framework of global change