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1.
New Phytol ; 230(4): 1421-1434, 2021 05.
Artigo em Inglês | MEDLINE | ID: mdl-33496969

RESUMO

Elevated atmospheric CO2 (eCa ) may benefit plants during drought by reducing stomatal conductance (gs ) but any 'water savings effect' could be neutralized by concurrent stimulation of leaf area. We investigated whether eCa enhanced water savings, thereby ameliorating the impact of drought on carbon and water relations in trees. We report leaf-level gas exchange and whole-plant and soil water relations during a short-term dry-down in two Eucalyptus species with contrasting drought tolerance. Plants had previously been established for 9 to 11 months in steady-state conditions of ambient atmospheric CO2 (aCa ) and eCa , with half of each treatment group exposed to sustained drought for 5 to 7 months. The lower stomatal conductance under eCa did not lead to soil moisture savings during the dry-down due to the counteractive effect of increased whole-plant leaf area. Nonetheless, eCa -grown plants maintained higher photosynthetic rates and leaf water potentials, making them less stressed during the dry-down, despite being larger. These effects were more pronounced in the xeric species than the mesic species, and in previously water-stressed plants. Our findings indicate that eCa may enhance plant performance during drought despite a lack of soil water savings, especially in species with more conservative growth and water-use strategies.


Assuntos
Secas , Eucalyptus , Dióxido de Carbono , Fotossíntese , Folhas de Planta , Árvores , Água
2.
New Phytol ; 222(2): 768-784, 2019 04.
Artigo em Inglês | MEDLINE | ID: mdl-30597597

RESUMO

The temperature response of photosynthesis is one of the key factors determining predicted responses to warming in global vegetation models (GVMs). The response may vary geographically, owing to genetic adaptation to climate, and temporally, as a result of acclimation to changes in ambient temperature. Our goal was to develop a robust quantitative global model representing acclimation and adaptation of photosynthetic temperature responses. We quantified and modelled key mechanisms responsible for photosynthetic temperature acclimation and adaptation using a global dataset of photosynthetic CO2 response curves, including data from 141 C3 species from tropical rainforest to Arctic tundra. We separated temperature acclimation and adaptation processes by considering seasonal and common-garden datasets, respectively. The observed global variation in the temperature optimum of photosynthesis was primarily explained by biochemical limitations to photosynthesis, rather than stomatal conductance or respiration. We found acclimation to growth temperature to be a stronger driver of this variation than adaptation to temperature at climate of origin. We developed a summary model to represent photosynthetic temperature responses and showed that it predicted the observed global variation in optimal temperatures with high accuracy. This novel algorithm should enable improved prediction of the function of global ecosystems in a warming climate.


Assuntos
Aclimatação/fisiologia , Fotossíntese/fisiologia , Plantas/metabolismo , Temperatura , Aclimatação/efeitos dos fármacos , Dióxido de Carbono/farmacologia , Respiração Celular/efeitos dos fármacos , Transporte de Elétrons/efeitos dos fármacos , Modelos Lineares , Modelos Biológicos , Fotossíntese/efeitos dos fármacos , Folhas de Planta/efeitos dos fármacos , Folhas de Planta/fisiologia , Plantas/efeitos dos fármacos , Ribulose-Bifosfato Carboxilase/metabolismo
3.
New Phytol ; 209(4): 1600-12, 2016 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-26526873

RESUMO

Models of tree responses to climate typically project that elevated atmospheric CO2 concentration (eCa ) will reduce drought impacts on forests. We tested one of the mechanisms underlying this interaction, the 'low Ci effect', in which stomatal closure in drought conditions reduces the intercellular CO2 concentration (Ci ), resulting in a larger relative enhancement of photosynthesis with eCa , and, consequently, a larger relative biomass response. We grew two Eucalyptus species of contrasting drought tolerance at ambient and elevated Ca for 6-9 months in large pots maintained at 50% (drought) and 100% field capacity. Droughted plants did not have significantly lower Ci than well-watered plants, which we attributed to long-term changes in leaf area. Hence, there should not have been an interaction between eCa and water availability on biomass, and we did not detect one. The xeric species did have higher Ci than the mesic species, indicating lower water-use efficiency, but both species exhibited similar responses of photosynthesis and biomass to eCa , owing to compensatory differences in the photosynthetic response to Ci . Our results demonstrate that long-term acclimation to drought, and coordination among species traits may be important for predicting plant responses to eCa under low water availability.


Assuntos
Dióxido de Carbono/farmacologia , Secas , Espaço Extracelular/metabolismo , Árvores/fisiologia , Biomassa , Clima , Eucalyptus/efeitos dos fármacos , Eucalyptus/fisiologia , Estômatos de Plantas/efeitos dos fármacos , Estômatos de Plantas/fisiologia , Transpiração Vegetal/efeitos dos fármacos , Transpiração Vegetal/fisiologia , Árvores/efeitos dos fármacos , Água
4.
Ann Bot ; 111(3): 479-88, 2013 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-23264237

RESUMO

BACKGROUND AND AIMS: A trade-off between shade tolerance and growth in high light is thought to underlie the temporal dynamics of humid forests. On the other hand, it has been suggested that tree species sorting on temperature gradients involves a trade-off between growth rate and cold resistance. Little is known about how these two major trade-offs interact. METHODS: Seedlings of Australian tropical and cool-temperate rainforest trees were grown in glasshouse environments to compare growth versus shade-tolerance trade-offs in these two assemblages. Biomass distribution, photosynthetic capacity and vessel diameters were measured in order to examine the functional correlates of species differences in light requirements and growth rate. Species light requirements were assessed by field estimation of the light compensation point for stem growth. RESULTS: Light-demanding and shade-tolerant tropical species differed markedly in relative growth rates (RGR), but this trend was less evident among temperate species. This pattern was paralleled by biomass distribution data: specific leaf area (SLA) and leaf area ratio (LAR) of tropical species were significantly positively correlated with compensation points, but not those of cool-temperate species. The relatively slow growth and small SLA and LAR of Tasmanian light-demanders were associated with narrow vessels and low potential sapwood conductivity. CONCLUSIONS: The conservative xylem traits, small LAR and modest RGR of Tasmanian light-demanders are consistent with selection for resistance to freeze-thaw embolism, at the expense of growth rate. Whereas competition for light favours rapid growth in light-demanding trees native to environments with warm, frost-free growing seasons, frost resistance may be an equally important determinant of the fitness of light-demanders in cool-temperate rainforest, as seedlings establishing in large openings are exposed to sub-zero temperatures that can occur throughout most of the year.


Assuntos
Luz , Plântula/crescimento & desenvolvimento , Árvores/crescimento & desenvolvimento , Austrália , Biomassa , Dióxido de Carbono/metabolismo , Temperatura Baixa , Estudos Transversais , Fotossíntese , Folhas de Planta/crescimento & desenvolvimento , Folhas de Planta/efeitos da radiação , Chuva , Estações do Ano , Plântula/efeitos da radiação , Especificidade da Espécie , Árvores/anatomia & histologia , Árvores/efeitos da radiação , Clima Tropical , Xilema/anatomia & histologia , Xilema/crescimento & desenvolvimento
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