Climate change in the tropics: drought effects on the phenology and eco-physiology of rainforest tree species

Nara Vogado investigated effects of climate change, specifically drought and elevated CO2, on the phenology and eco-physiology of tree species from the Wet Tropics. She found that phenological responses are influenced by both climate and physiological processes, and vary with species and their capacity to adapt

Assessing the effects of a drought experiment on the reproductive phenology and ecophysiology of a wet tropical rainforest community

Climate change is expected to increase the intensity and occurrence of drought in tropical regions, potentially affecting the phenology and physiology of tree species. Phenological activity may respond to a drying and warming environment by advancing reproductive timing, and/or diminishing the production of flowers and fruits. These changes have the potential to disrupt important ecological processes, with potentially wide-ranging effects on tropical forest function. Here, we analysed the monthly flowering and fruiting phenology of a tree community (337 individuals from 30 species) over seven years in a lowland tropical rainforest in north-eastern Australia, and its response to a through fall exclusion drought experiment (TFE) that was carried out from 2016 to 2018 (three years), excluding approximately 30% of rainfall. We further examined the eco-physiological effects of the TFE on the elemental (C:N) and stable isotope (d13C and d15N) composition of leaves, and on the stable isotope composition (d13C and d18O) of stem wood of four tree species. At the community level, there was no detectable effect of the TFE on flowering activity overall but there was a significant effect recorded on fruiting and varying responses from the selected species. The reproductive phenology and physiology of the four species examined in detail were largely resistant to impacts of the TFE treatment. One canopy species in the TFE significantly increased in fruiting and flowering activity whereas one understory species decreased significantly in both. There was a significant interaction between the TFE treatment and season on leaf C:N for two species. Stable isotope responses were also variable among species, indicating species-specific responses to the TFE. Thus, we did not observe consistent patterns in physiological and phenological changes in the tree community within the three years of TFE treatment examined in this study

Fenologia e dendrocronologia de duas espécies de Fabaceae em uma área de cerrado no sudeste do Brasil

Phenology studies the occurrence of repetitive biological events and their relationship especially with climate, and also with biotic factors such as pollinators and seed dispersers. Dendrochronology studies the growth rings of trees, and the response of trees to climate change, allowing also estimating the age of the tree and revealing information about its ecology. Furthermore, dendrochronology allows the reconstruction of the climate through the analysis of the anatomy of the stem, since plants record, in the form of growth rings, signals of temperature changes and precipitation that affect their growth and dormancy. Within the growth rings it is possible to find the pattern of carbon and oxygen isotopes, which can reveal important ecological information such as the influence of seasonality on plant growth and phenology, as well as the source of water use, seasonality and climate changes. In this sense, the cyclic rings and isotopes of carbon and oxygen are anatomical and physiological responses that, related to a particular reproductive or vegetative phenology activity, may allow phenological reconstruction and the evaluation of climatic factors influencing these reconstructed patterns, allowing the understanding of climate changes effects on plants. This study aimed to (1) analyze eight years of phenology of Fabaceae (Anadenanthera peregina var falcata and Pterodon pubescens) in Itirapina, São Paulo, and determine its relationship to climate variations; (2) study the pattern formation of growth rings, looking for signs that enable the understanding of the influence of climate on the phenology and growth of both species; (3) determine the influence of climate on the phenology and growth of the species through the pattern of carbon and oxygen stable isotopes. In Chapter 1 we found that both species have their growth influenced by climate and seasonality of the Cerrado, responding to different climate variables. In Chapter 2 we...A fenologia estuda a ocorrência de eventos biológicos repetitivos e sua relação principalmente com o clima, e também com os fatores bióticos como polinizadores e dispersores de sementes. A dendrocronologia estuda os anéis de crescimento das árvores e, com isso, a resposta da árvore as mudanças do clima, podendo também estimar a idade da árvore e revelar informações de sua ecologia. Além disso, a dendrocronologia possibilita a reconstrução do clima pela análise da anatomia do lenho, uma vez que a planta registra na forma de anéis sinais das mudanças de temperatura e da precipitação que afetaram seu crescimento e dormência. Dentro dos anéis de crescimento é possível entrar o padrão de isótopos tanto de carbono quanto de oxigênio, que podem revelar informações ecológicas importantes, como a influência da sazonalidade no crescimento da planta e sua fenologia, bem como a fonte de uso da água, sua sazonalidade sob influência do clima e suas mudanças. Neste sentido, os anéis cíclicos e seus isótopos de carbono e oxigênio são respostas anatômicas e fisiológicas que, se relacionadas a uma determinada fenofase reprodutiva ou vegetativa, podem permitir uma reconstrução fenológica e uma avaliação dos fatores climáticos influenciando esses padrões reconstruídos, com implicações ecológicas, no entendimento dos efeitos de mudanças climáticas nas plantas. Este trabalho teve como objetivo (1) analisar oito anos de fenologia de Fabaceae (Anadenanthera peregina var falcata e Pterodon pubescens) em Itirapina, São Paulo, e determinar a sua relação com as variações climáticas; (2) estudar o padrão de formação dos anéis de crescimento, procurando encontrar sinais que possibilitem o entendimento da influência do clima sobre a fenologia e o crescimento de ambas as espécies; (3) verificar a influência do clima sobre a fenologia e o crescimento das espécies através do padrão de isótopos estáveis de...Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Directional change in leaf dry matter delta C-13 during leaf development is widespread in C-3 plants

Background and aims: The stable carbon isotope ratio of leaf dry matter (delta C-13(p)) is generally a reliable recorder of intrinsic water-use efficiency in C-3 plants. Here, we investigated a previously reported pattern of developmental change in leaf delta C-13(p) during leaf expansion. whereby emerging leaves are initially C-13-enriched compared to mature leaves on the same plant, with their delta C-13(p) decreasing during leaf expansion until they eventually take on the delta C-13(p) of other mature leaves. Methods: We compiled data to test whether the difference between mature and young leaf delta C-13(p) differs between temperate and tropical species, or between deciduous and evergreen species. We also tested whether the developmental change in delta C-13(p) is indicative of a concomitant change in intrinsic water-use efficiency. To gain further insight, we made online measurements of (13)C( )discrimination (Delta C-13) in young and mature leaves. Key Results: We found that the delta C-13(p) difference between mature and young leaves was significantly larger for deciduous than for evergreen species (-2.1 parts per thousand vs. -1.4 parts per thousand, respectively). Counter to expectation based on the change in delta C-13(p), intrinsic water-use efficiency did not decrease between young and mature leaves: rather, it did the opposite. The ratio of intercellular to ambient CO2 concentrations (c(i)/c(a))was significantly higher in young than in mature leaves (0.86 vs. 0.72, respectively), corresponding to lower intrinsic water-use efficiency. Accordingly, instantaneous Delta C-13 was also higher in young than in mature leaves. Elevated c(i)/c(a) and Delta C-13 in young leaves resulted from a combination of low photosynthetic capacity and high day respiration rates. Conclusion: The decline in leaf delta C-13(p) during leaf expansion appears to reflect the addition of the expanding leaf's own C-13-depleted photosynthetic carbon to that imported from outside the leaf as the leaf develops. This mixing of carbon sources results in an unusual case of isotopic deception: less negative delta C-13(p) in young leaves belies their low intrinsic water-use efficiency

Elevated temperature and CO2 cause differential growth and drought survival responses in Eucalypt species from contrasting habitats

Climate change scenarios predict increasing atmospheric CO2 concentrations ([CO2]), temperatures and droughts in tropical regions. Individually, the effects of these climate factors on plants are well established, whereas experiments on the interactive effects of a combination of factors are rare. Moreover, how these environmental factors will affect tree species along a wet to dry gradient (e.g., along tropical forest–savanna transitions) remains to be investigated. We hypothesized that under the simulated environmental conditions, plant growth, physiological performance and survivorship would vary in a manner consistent with the species’ positions of origin along this gradient. In a glasshouse experiment, we raised seedlings of three Eucalyptus species, each occurring naturally in a wet forest, savanna and forest–savanna ecotone, respectively. We evaluated the effect of drought, elevated temperature (4 °C above ambient glasshouse temperature of 22 °C) and elevated temperature in combination with elevated [CO2] (400 ppm [CO2] above ambient of 400 ppm), on seedling growth, survivorship and physiological responses (photosynthesis, stomatal conductance and water-use efficiency). Elevated temperature under ambient [CO2] had little effect on growth, biomass and plant performance of well-watered seedlings, but hastened mortality in drought-affected seedlings, affecting the forest and ecotone more strongly than the savanna species. In contrast, elevated [CO2] in combination with elevated temperatures delayed the appearance of drought stress symptoms and enhanced survivorship in drought-affected seedlings, with the savanna species surviving the longest, followed by the ecotone and forest species. Elevated [CO2] in combination with elevated temperatures also enhanced growth and biomass and photosynthesis in well-watered seedlings of all species, but modified shoot:root biomass partitioning and stomatal conductance differentially across species. Our study highlights the need for a better understand of the interactive effects of elevated [CO2], temperature and drought on plants and the potential to upscale these insights for understanding biome changes

Phenology, seed germination, and genetics explains the reproductive strategies of Diospyros lasiocalyx (Mart.) B. Wall

Diospyros lasiocalyx (Mart.) B. Wall. is a dioecious tree species found in the threatened and fragmented Brazilian Cerrado. Its fleshy fruits, which are consumed extensively by wildlife, make the species ideal for use in restoration. This study includes a ten-year phenological observation, germination tests, and analysis of molecular markers to understand the reproductive strategy of D. lasiocalyx based on samples from three populations in two Cerrado ecosystems in São Paulo State, Brazil. The within population reproductive phenological pattern presented low synchrony, indicating a lack of sexual reproduction. The vegetative phenological pattern was well pronounced, with the peak of senescence occurring at the end of the dry season, just before leaf flushing. A small number of unique genets were found, indicating asexual reproduction and low genotypic diversity in the studied populations. The absence of inbreeding and the presence of ramets (stems) suggest that reproduction mainly occurs by apomixis and vegetative propagation, with some mating among unrelated stems and a low germination rate. Our study indicates that D. lasiocalyx can colonize harsh environments such as the Cerrado using alternative asexual reproductive strategies, while simultaneously attracting many seed dispersers