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Jatropha curcas is a drought-tolerant plant that maintains its photosynthetic pigments under prolonged drought, and quickly regains its photosynthetic capacity when water is available. It has been reported that drought stress leads to increased thermal dissipation in PSII, but that of PSI has been barely investigated, perhaps due to technical limitations in measuring the PSI absolute quantum yield. In this study, we combined biochemical analysis and spectroscopic measurements using an integrating sphere, and verified that the quantum yields of both photosystems are temporarily down-regulated under drought. We found that the decrease in the quantum yield of PSII was accompanied by a decrease in the core complexes of PSII while light-harvesting complexes are maintained under drought. In addition, in drought-treated plants, we observed a decrease in the absolute quantum yield of PSI as compared with the well-watered control, while the amount of PSI did not change, indicating that non-photochemical quenching occurs in PSI. The down-regulation of both photosystems was quickly lifted in a few days upon re-watering. Our results indicate, that in J. curcas under drought, the down-regulation of both PSII and PSI quantum yield protects the photosynthetic machinery from uncontrolled photodamage. [ABSTRACT FROM AUTHOR]

Radial growth responses to climate were studied in two species of birch broadly distributed across Kamchatka Peninsula. Wood cores were obtained in different locations and environments, from upper to lower treelines, and from wet maritime sites at the Pacific to the subcontinental interior of the peninsula. Response functions were calculated using the four longest meteorological records (1920s-2000) in Kamchatka. In Betula ermanii Cham., the dominant species in mountains and maritime woodlands, ring width in high-elevation (500-600 m) trees increased with warm and less rainy June and July and decreased with rainy/snowy cool weather during the prior September and October. Radial growth in B. ermanii low-elevation trees increased with higher winter precipitation, suggesting that water from melting snow prevents water stress and possibly desiccation in low-elevation trees. In Betula platyphylla Sukaczev, a common taiga species in interior Kamchatka, low summer temperatures limited growth at its upper distributional limit (300-350 m) and in cool, wet sites dominated by Picea ajanensis Lindl. et Gord. On drier sites dominated by Larix cajanderii Mayr., growth was limited by warm April and dry June weather. Variable responses along elevation--continentality gradients reinforce the necessity of a site-dependent differentiation for the assessment of impacts of climate change on species performance and geographic range shifts. Resume: Les reponses de la croissance radiale au climat ont ete etudiees chez deux especes de bouleau distribuees sur l'ensemble de la peninsule de Kamchatka. Des carottes de bois ont ete prelevees a differents endroits et dans differents environnements, de la limite superieure a la limite inferieure des arbres et sur des stations maritimes humides du cote du Pacifique jusqu'a l'interieur subcontinental de la peninsule. Des fonctions de reponse ont ete calculees en utilisant les quatre plus longs releves meteorologiques (annees 1920 a 2000) du Kamchatka. Chez Betula ermanii Cham., l'espece dominante dans les montagnes et les boises maritimes, la largeur des cernes annuels chez les arbres situes a haute altitude (500-600 m) augmentait avec le temps chaud et moins pluvieux en juin et juillet; elle diminuait avec le temps frais et pluvieux ou neigeux durant les mois de septembre et octobre precedents. La croissance radiale destiges de B. ermanii situees a basse altitude augmentait avec la quantite de precipitations hivernales, indiquant que l'eau provenant de la fonte des neiges previent les stress hydriques et possiblement la dessiccation chez les arbres situes a basse altitude. Chez Betula platyphylla Sukaczev, une espece commune dans la taiga a l'interieur du Kamchatka, les temperatures basses durant l'ete limitaient la croissance a sa limite superieure de distribution (300-350 m) et sur les stations fraiches et humides dominees par Picea ajanensis Lindl. et Gord. Sur les stations plus seches dominees par Larix cajanderii Mayr., la croissance etait limitee par le temps chaud en avril et sec en juin. Les reponses variables le long de gradients d'altitude ou de continentalite renforcent la necessite d'une differenciation basee sur le site pour l'evaluation des impacts des changements climatiques sur la performance des especes et la modification de leur etendue geographique. [Traduit par la Redaction], Introduction The boreal forests have experienced a significant rise in mean surface temperatures over the last century (Briffa et al. 1995). This has increased the importance of understanding the patterns [...]