Junipers and pines exhibit contrasting patterns of growth decline and mortality with climate change-type warming and drought; yet, the underlying physiological mechanisms are not fully understood. Does warming exacerbate the effects of drought on gas exchange physiology and growth? Do the combined effects of drought and warming differ for pines and junipers? To what extent do isohydric vs. anisohydric responses to water limitation in pines and junipers constrain net leaf CO2 exchange and plant growth response to drought and warming? To address these questions, we compared responses of leaf gas exchange and growth in seedlings of juniper (Juniperus scopulorum, J. virginiana) and pine (Pinus edulis, P. taeda) species of contrasting arid and mesic origin in a study of combined warming (ambient, +1.8 °C) and enhanced summer drought (long-term mean, -40%). Warming and enhanced summer drought each reduced photosynthesis and growth and effects were largely independent, suggesting that warming exacerbates drought effects on growth. Enhanced summer drought and warming had distinct impacts on photosynthetic carbon gain that were differentially revealed depending upon soil water content. Warming reduced light-saturated net photosynthesis (Asat) under low soil water contents, whereas carry-over effects of drought treatment were evident under well-watered conditions. Short-term soil drying led to greater reduction of Asat in pines (-51%) rather than junipers (-30%). Under short-term water-limited conditions, Asat and gs were about two-times higher for junipers compared to pines. Relative growth rate of junipers declined with warming (-28%) and drought (-50%) treatments. In contrast, pine growth and Asat declined more with warming than drought. Only P. edulis exhibited increased mortality in response to warming and drought, reaching 75% in the combined warming and drought treatment. Diminished sensitivity of R to water limitations, coupled with steeper reductions in Asat with decreasing soil water content in isohydric pines compared to anisohydric junipers could account for the greater sensitivity of pines to warming and drought under climate change.

No description available.

La raréfaction des ressources en eau associée au changement climatique menace particulièrement la durabilité de la viticulture en climat Méditerranéen. Pour y faire face, la création ou le choix de cépages économes en eau et suffisamment vigoureux en cas de déficit hydrique se présente comme un levier important. Une compréhension approfondie des mécanismes qui gouvernent le maintien de l'état hydrique par la plante est indispensable pour avancer dans cette direction. Dans ce travail les déterminants génétiques et physiologiques de l'utilisation de l'eau ont été explorés chez la vigne. Une descendance F1, issue d'un croisement entre les cépages Syrah et Grenache, a été soumise à deux scénarios hydriques dans des pots (bonne irrigation et déficit modéré) en combinant de nouveaux outils de phénotypage, une démarche de génétique quantitative (pour la détection de QTLs) et des approches physiologiques. L'analyse de l'architecture génétique du maintien du potentiel hydrique par la plante, plus ou moins efficace en cas de déficit hydrique (i.e. iso- ou aniso-hydrique), a révélé un double déterminisme, impliquant non seulement la régulation stomatique de la transpiration mais également le maintien de la conductance hydraulique à travers la plante. Nous avons démontré l'existence d'une action indirecte de l'acide abscissique sur la fermeture stomatique à travers une diminution de la conductance hydraulique dans la feuille avec une variabilité génétique reliée aux comportements iso- ou aniso-hydriques. Par ailleurs, nous avons mis en évidence une variabilité génétique importante de la transpiration nocturne, liée à celle de l'efficience d'utilisation de l'eau, avec des déterminants génétiques et physiologiques que nous avons identifiés. Au-delà de l'utilité des QTLs détectés pour l'amélioration variétale, les résultats originaux de ce travail démontrent l'intérêt de la génétique quantitative pour progresser dans la compréhension de mécanismes physiologiques. / In Mediterranean regions, water scarcity associated with climate change particularly threatens the sustainability of viticulture. Breeding grapevine for reduced water use and maintained production is therefore of major interest. This requires a comprehensive knowledge of the plant physiological responses to drought. In this study we focused on the determinism of transpiration rate as a key trait regulating water status in plant tissues, and on its relationship with water-use efficiency (WUE). We used a F1 progeny from a cross between cultivars Syrah and Grenache and combined powerful phenotyping tools on potted plants submitted to either well-watered or mild deficit conditions with quantitative genetics (for QTL detection) and physiological experiments. Analysis of the genetic control of water status maintenance in the plant, more or less efficient under soil water deficit (i.e. iso- or anisohydric), revealed a dual physiological determinism with a key role for plant hydraulic conductance beside that of stomatal control of transpiration. An indirect role of abscisic acid on stomatal conductance was also evidenced, mediated by the downregulation of leaf hydraulic conductance, with a genetic variability which correlated with genetic variation in iso- or aniso-hydric behaviour. We then revealed wide genetic variations in nocturnal transpiration, which correlated with variations in water use efficiency, and identified corresponding genetic and physiological determinants. In a final switch to the field, we showed consistency between QTLs detected for daytime WUE in pots and in the vineyard. Beyond the potential interest of the QTLs detected in this study for breeding prospects, this work demonstrated the benefits of quantitative genetics to shed light on ecophysiological and physiological processes.

CoordenaÃÃo de AperfeÃoamento de Pessoal de NÃvel Superior / Por que as diferentes espÃcies de angiospermas nÃo sÃo igualmente bem-sucedidas em todos os ambientes do planeta? Uma das explicaÃÃes recorrentes à baseada no conceito de trade-off (demanda conflitante). Entende-se por demanda conflitante a relaÃÃo negativa entre traÃos funcionais que nÃo podem ser otimizados simultaneamente pela planta. As variaÃÃes nos traÃos funcionais entre plantas sÃo interpretadas como adaptaÃÃes das espÃcies a condiÃÃes ambientais em resposta à aquisiÃÃo de recursos necessÃrios para seu desenvolvimento. A disponibilidade hÃdrica pode ser considerada o principal fator ambiental que afeta quase todos os processos fisiolÃgicos e fenolÃgicos das plantas de forma direta e/ou indireta, portanto, modula diversas demandas conflitantes. Nosso objetivo principal à o de compreender quais as estratÃgias hidrÃulicas e o comportamento fisiolÃgico em espÃcies decÃduas e sempre verdes em resposta à seca. No primeiro capÃtulo, analisamos a variaÃÃo funcional entre espÃcies decÃduas e sempre verdes para compreender as divergÃncias nas estratÃgias de tolerÃncia e evitaÃÃo à seca. Mensuramos 17 traÃos funcionais foliares em 17 espÃcies decÃduas e cinco sempre verdes. AlÃm disso, mensuramos a condutÃncia estomÃtica (gs), taxa de fotossÃntese por Ãrea e massa (AÃrea/Amassa) e a eficiÃncia instantÃnea e intrÃnseca no uso da Ãgua (EUAi e EUA) durante a estaÃÃo chuvosa. Verificamos que as espÃcies decÃduas exibiram maior Amassa, menor longevidade foliar (LF) e massa foliar especÃfica (MFE) quando comparadas Ãs sempre verdes. EspÃcies decÃduas e sempre verdes apresentaram demanda conflitante entre tolerÃncia à seca e capacidade fotossintÃtica, quanto maior a LF menor a Amassa. Embora as espÃcies decÃduas tenham apresentado maior Amassa e gs do que Ãs sempre verdes, nÃo observamos diferenÃas significativas na EUAi e EUA. As diferenÃas nas estratÃgias de evitaÃÃo e tolerÃncia à seca entre espÃcies decÃduas e sempre verdes sÃo claramente observadas indistintamente à disponibilidade hÃdrica. No segundo capÃtulo, avaliamos se hà divergÃncia ou convergÃncia nas estratÃgias hidrÃulicas em espÃcies decÃduas e sempre verdes e como respondem aos efeitos da seca. Observamos mensalmente a fenologia foliar relacionando-a com o dÃficit de pressÃo de vapor do ar (DPV) e o conteÃdo de Ãgua no solo (CAS). Realizamos mensalmente mediÃÃes do potencial hÃdrico antes do amanhecer e relacionamos com a densidade da madeira (ρwood). Observamos as variaÃÃes no comportamento estomÃtico e no potencial hÃdrico diÃrio, e por fim, mensuramos e comparamos 17 traÃos funcionais foliares entre os grupos fenolÃgicos. A separaÃÃo das espÃcies em grupos baseados apenas na LF fornece boa compreensÃo sobre estratÃgias hidrÃulicas em respostas à seca. EspÃcies decÃduas exibem diferentes estratÃgias (isohÃdrica/anisohÃdrica), independente da ρwood. EspÃcies sempre verdes nÃo exibem diferenÃa de estratÃgia, sendo apenas anisohÃdricas. Consideramos que traÃos hidrÃulicos como o gradiente no potencial hÃdrico entre raÃzes e folhas (ΔΨplanta), o potencial hÃdrico responsÃvel por 50% do fechamento estomÃtico (ΨSC) e a diferenÃa no potencial hÃdrico sazonal (ΔΨsazonal) sÃo chaves para identificaÃÃo de estratÃgias hidrÃulicas em espÃcies de ecossistemas sazonalmente secos / Why the different species of angiosperms not are equally successful in all environments of planet? One recurrent explanation is based in concept of trade-off. It is understood trade-off per the negative relation between functional traits that cannot be optimized simultaneously by the plant. The variations in functional traits between plants are understood how adaptations of the species to environmental conditions in response at resource acquisition necessary for development. The hydric availability can be considerate the main environmental factor that affect almost all physiological and phenological processes of plants of direct and/or indirect form, therefore, modulating various trade-off. Our main goal is understand which hydraulic strategies and the physiology behavior in deciduous and evergreen species in response to drought. In first chapter, we analyzed the functional variation between deciduous and evergreen species for understand the divergence in the strategies of avoidance and tolerance to drought. We measured 17 leaf functional traits in 17 deciduous and five evergreen species. Furthermore, we measured the stomatal conductance (gs), photosynthetic rate based area and mass (Aarea/Amass) and the instantaneous and intrinsic water use efficient (WUEi and WUE) during the rainy season. We checked that the deciduous species exhibited bigger Amass, less leaf lifespan (LL) and leaf specific mass (LSM) when compared with evergreen species. Deciduous and evergreen species showed trade-off between drought tolerance and photosynthetic capacity, the bigger LF is the less the Amass. Although the deciduous species have showed larger Amass and gs than the evergreen species, we do not observed significant difference in WUEi and WUE. The difference in the strategies of drought avoidance and tolerance between deciduous and evergreen species are clearly observed indistinctly to hydric availability. In second chapter, we evaluated if are divergence or convergence in the hydraulic strategies in deciduous and evergreen species and how they respond to effects of the drought. We observed monthly the leaf phenology by relating with the vapor pressure deficit (VPD) and the soil water content (SWC). We performed monthly measurements of water potential predawn and related with the wood density (ρwood). We observed the variation in stomatal behavior and in daily water potential and lastly measurements and compared 17 leaf functional traits between the phenological groups. The separation of species in groups based only LF provides good understanding about hydraulic strategies in response to drought. Deciduous species exhibited different strategies (isohydric/anisohydric) independently of ρwood. Evergreen species do not exhibit difference of strategy, it is only anisohydric. We regard that hydraulic traits how the water potential gradient from roots to shoots (ΔΨplant), the water potential responsible for 50% of stomatal closure (ΨSC) and the difference in seasonal water potential (ΔΨseasonal) are key for identification of hydraulic strategies in species of the seasonally dry ecosystems

No description available.