Atmospheric and climate change will expose tropical forests to conditions they have not experienced in millions of years. To better understand the consequences of this change, we studied ...photosynthetic acclimation of the neotropical tree species Tabebuia rosea to combined 4°C warming and twice‐ambient (800 ppm) CO2. We measured temperature responses of the maximum rates of ribulose 1,5‐bisphosphate carboxylation (VCMax), photosynthetic electron transport (JMax), net photosynthesis (PNet), and stomatal conductance (gs), and fitted the data using a probabilistic Bayesian approach. To evaluate short‐term acclimation plants were then switched between treatment and control conditions and re‐measured after 1–2 weeks. Consistent with acclimation, the optimum temperatures (TOpt) for VCMax, JMax and PNet were 1–5°C higher in treatment than in control plants, while photosynthetic capacity (VCMax, JMax, and PNet at TOpt) was 8–25% lower. Likewise, moving control plants to treatment conditions moderately increased temperature optima and decreased photosynthetic capacity. Stomatal density and sensitivity to leaf‐to‐air vapour pressure deficit were not affected by growth conditions, and treatment plants did not exhibit stronger stomatal limitations. Collectively, these results illustrate the strong photosynthetic plasticity of this tropical tree species as even fully developed leaves of saplings transferred to extreme conditions partially acclimated.
We report thermal acclimation and CO2 acclimation of photosynthesis of saplings of tropical tree species Tabebuia rosea grown at +4°C and 800 ppm CO2, even after brief (~2 weeks) exposure. This was underpinned by changes in biochemical parameters VCMax and JMax, not by changes in stomatal conductance.
Exceeding thermal thresholds causes irreversible damage and ultimately loss of leaves. The lowland tropics are among the warmest forested biomes, but little is known about heat tolerance of tropical ...forest plants. We surveyed leaf heat tolerance of sun‐exposed leaves from 147 tropical lowland and pre‐montane forest species by determining the temperatures at which potential photosystem II efficiency based on chlorophyll a fluorescence started to decrease (TCrit) and had decreased by 50% (T50). TCrit averaged 46.7°C (5th–95th percentile: 43.5°C–49.7°C) and T50 averaged 49.9°C (47.8°C–52.5°C). Heat tolerance partially adjusted to site temperature; TCrit and T50 decreased with elevation by 0.40°C and 0.26°C per 100 m, respectively, while mean annual temperature decreased by 0.63°C per 100 m. The phylogenetic signal in heat tolerance was weak, suggesting that heat tolerance is more strongly controlled by environment than by evolutionary legacies. TCrit increased with the estimated thermal time constant of the leaves, indicating that species with thermally buffered leaves maintain higher heat tolerance. Among lowland species, T50 increased with leaf mass per area, suggesting that in species with structurally more costly leaves the risk of leaf loss during hot spells is reduced. These results provide insight in variation in heat tolerance at local and regional scales.
To determine the variation in leaf heat tolerance and investigate what explains such variation, we measured heat tolerance traits for 147 plant species of tropical lowland and pre‐montane forests in Panama. Variation in heat tolerance was related to elevation and leaf traits associated with leaf thermoregulation and leaf construction costs, but not to phylogenetic relatedness of the species.
• Use of carbon isotope ratio (δ13C) to resolve photosynthetic pathways ( C3, C4or CAM) has limitations imposed by the use of intermediate photosynthetic modes by certain plant taxa. • Diel ...gas-exchange patterns, leaf δ13C values and nocturnal tissue acidification were determined for 50 Bromeliaceae. • δ13C values for well watered plants reflected the proportion of daily CO2uptake occurring at night. Thirteen per cent of species with δ13C values typical of C3plants (i.e. from -22.6 to -31.5‰) showed nocturnal acidification and either a small proportion (< 10%) of daily CO2uptake occurring nocturnally or internal CO2recycling during part of the night. None altered CAM expression in response to short-term drought, but the contribution of CAM to daily carbon gain became proportionally more important as C3CO2uptake failed. • Surveys of plant communities using solely the carbon isotope technique under-estimate the number of CAM-equipped plants.
The carbon isotope composition of the halophyte Mesembryanthemum crystallinum L. (Aizoaceae) changes when plants are exposed to environmental stress and when they shift from C3 to crassulacean acid ...metabolism (CAM). We examined the coupling between carbon isotope composition and photosynthetic pathway by subjecting plants of different ages to salinity and humidity treatments. Whole shoot delta13C values became less negative in plants that were exposed to 400 mM NaCl in the hydroponic solution. The isotopic change had two components: a direct NaCl effect that was greatest in plants still operating in the C3 mode and decreased proportionally with increasing levels of dark fixation, and a second component related to the degree of CAM expression. Ignoring the presumably diffusion-related NaCl effect on carbon isotope ratios results in an overestimation of nocturnal CO2 gain in comparison to an isotope versus nocturnal CO2 gain calibration established previously for C3 and CAM species grown under well-watered conditions. It is widely taken for granted that the shift to CAM in M. crystallinum is partially under developmental control and that CAM is inevitably expressed in mature plants. Plants, cultivated under non-saline conditions and high relative humidity (RH) for up to 63 days, maintained diel CO2 gas-exchange patterns and delta13C values typical of C3 plants. However, a weak CAM gas-exchange pattern and an increase in delta13C value were observed in non-salt-treated plants grown at reduced RH. These observations are consistent with environmental control rather than developmental control of the induction of CAM in mature M. crystallinum under non-saline conditions.
Photosynthetic carbon uptake by tropical forests is of critical importance in regulating the earth's climate, but rising temperatures threaten this stabilizing influence of tropical forests. Most ...research on how temperature affects photosynthesis focuses on fully sun-exposed leaves, and little is known about shade leaves, even though shade leaves greatly outnumber sun leaves in lowland tropical forests. We measured temperature responses of light-saturated photosynthesis, stomatal conductance, and the biochemical parameters VCMax (maximum rate of RuBP carboxylation) and JMax (maximum rate of RuBP regeneration, or electron transport) on sun and shade leaves of mature tropical trees of three species in Panama. As expected, biochemical capacities and stomatal conductance were much lower in shade than in sun leaves, leading to lower net photosynthesis rates. However, the key temperature response traits of these parameters-the optimum temperature (TOpt) and the activation energy-did not differ systematically between sun and shade leaves. Consistency in the JMax to VCMax ratio further suggested that shade leaves are not acclimated to lower temperatures. For both sun and shade leaves, stomatal conductance had the lowest temperature optimum (~25 °C), followed by net photosynthesis (~30 °C), JMax (~34 °C) and VCMax (~38 °C). Stomatal conductance of sun leaves decreased more strongly with increasing vapor pressure deficit than that of shade leaves. Consistent with this, modeled stomatal limitation of photosynthesis increased with increasing temperature in sun but not shade leaves. Collectively, these results suggest that modeling photosynthetic carbon uptake in multi-layered canopies does not require independent parameterization of the temperature responses of the biochemical controls over photosynthesis of sun and shade leaves. Nonetheless, to improve the representation of the shade fraction of carbon uptake dynamics in tropical forests, better understanding of stomatal sensitivity of shade leaves to temperature and vapor pressure deficit will be required.
Smart contracts are a promising means of formalizing and reliably enforcing agreements between entities using distributed ledger technology (DLT). Research has revealed that a significant number of ...smart contracts are subject to programming flaws, making them vulnerable to attacks and leading to detrimental effects, such as asset loss. Researchers and developers call for a thorough analysis of challenges to identify their causes and propose solutions. To respond to these calls, we conducted two literature reviews and diverse expert interviews and synthesized scattered knowledge on challenges and solutions. We identified 29 challenges (e.g., code visibility, code updateability, and encapsulation) and 60 solutions (e.g., gas limit specification, off-ledger computations, and shadowing). Moreover, we developed 20 software design patterns (SDPs) in collaboration with smart contract developers. The SDPs help developers adjust their programming habits and thus support them in their daily development practices. Our results provide actionable knowledge for smart contract developers to overcome the identified challenges and offer support for comparing smart contract integration concepts across three fundamentally different DLT protocols (i.e., Ethereum, EOSIO, and Hyperledger Fabric). Moreover, we support developers in becoming aware of peculiarities in smart contract development and the resulting benefits and drawbacks.
Summary
More frequent droughts and rising temperatures pose serious threats to tropical forests. When stomata are closed under dry and hot conditions, plants lose water through leaf cuticles, but ...little is known about cuticle conductance (gmin) of tropical trees, how it varies among species and environments, and how it is affected by temperature.
We determined gmin in relation to temperature for 24 tropical tree species across a steep rainfall gradient in Panama, by recording leaf drying curves at different temperatures in the laboratory.
In contrast with our hypotheses, gmin did not differ systematically across the rainfall gradient; species differences did not reflect phylogenetic patterns; and in most species gmin did not significantly increase between 25 and 50°C. gmin was higher in deciduous than in evergreen species, in species with leaf trichomes than in species without, in sun leaves than in shade leaves, and tended to decrease with increasing leaf mass per area across species. There was no relationship between stomatal and cuticle conductance.
Large species differences in gmin and its temperature response suggest that more frequent hot droughts may lead to differential survival among tropical tree species, regardless of species’ position on the rainfall gradient.
Many succulent species are characterized by the presence of Crassulacean acid metabolism (CAM) and/or elevated bulk hydraulic capacitance (CFT). Both CAM and elevated CFT substantially reduce the ...rate at which water moves through transpiring leaves. However, little is known about how these physiological adaptations are coordinated with leaf vascular architecture.
The genus Clusia contains species spanning the entire C3-CAM continuum, and also is known to have >5-fold interspecific variation in CFT. We used this highly diverse genus to explore how interspecific variation in leaf vein density is coordinated with CAM and CFT.
We found that constitutive CAM phenotypes were associated with lower vein length per leaf area (VLA) and vein termini density (VTD), compared to C3 or facultative CAM species. However, when vein densities were standardized by leaf thickness, this value was higher in CAM than C3 species, which is probably an adaptation to overcome apoplastic hydraulic resistance in deep chlorenchyma tissue. In contrast, CFT did not correlate with any xylem anatomical trait measured, suggesting CAM has a greater impact on leaf transpiration rates than CFT.
Our findings strongly suggest that CAM photosynthesis is coordinated with leaf vein densities. The link between CAM and vascular anatomy will be important to consider when attempting to bioengineer CAM into C3 crops.
BackgroundIn patients with ST-segment elevation myocardial infarction (STEMI), it is unknown how patient delay modulates the beneficial effects of timely reperfusion.AimsTo assess the prognostic ...significance of a contact-to-balloon time of less than 90 min on in-hospital mortality in different categories of symptom-onset-to-first-medical-contact (S2C) times.MethodsA total of 20 005 consecutive patients from the Feedback Intervention and Treatment Times in ST-segment Elevation Myocardial Infarction (FITT-STEMI) programme treated with primary percutaneous coronary intervention (PCI) were included.ResultsThere were 1554 deaths (7.8%) with a J-shaped relationship between mortality and S2C time. Mortality was 10.0% in patients presenting within 1 hour, and 4.9%, 6.0% and 7.3% in patient groups with longer S2C intervals of 1–2 hours, 2–6 hours and 6–24 hours, respectively. Patients with a short S2C interval of less than 1 hour (S2C<60 min) had the highest survival benefit from timely reperfusion with PCI within 90 min (OR 0.27, 95% CI 0.23 to 0.31, p<0.0001) as compared with the three groups with longer S2C intervals of 1 hour<S2C≤2 hours (OR 0.44, 95% CI 0.33 to 0.59, p<0.0001), 2 hours<S2C≤6 hours (OR 0.49, 95% CI 0.38 to 0.64, p<0.0001) and 6 hours<S2C≤24 hours (OR 0.42, 95% CI 0.30 to 0.58, p<0.0001).ConclusionsTimely reperfusion with a contact-to-balloon time of less than 90 min is most effective in patients presenting with short S2C intervals of less than 1 hour, but has also beneficial effects in patients with S2C intervals of up to 24 hours.Trial registration numberNCT00794001.
The distinctive foliar trichome of Bromeliaceae has promoted the evolution of an epiphytic habit in certain taxa by allowing the shoot to assume a significant role in the uptake of water and mineral ...nutrients. Despite the profound ecophysiological and taxonomic importance of this epidermal structure, the functions of nonabsorbent trichomes in remaining Bromeliaceae are not fully understood. The hypothesis that light reflection from these trichome layers provides photoprotection was not supported by spectroradiometry and fluorimetry in the present study; the mean reflectance of visible light from trichome layers did not exceed 6.4% on the adaxial surfaces of species representing a range of ecophysiological types nor was significant photoprotection provided by their presence. Several reports suggesting water repellency in some terrestrial Bromeliaceae were investigated. Scanning electron microscopy (SEM) and a new technique-fluorographic dimensional imaging (FDI)-were used to assess the interaction between aqueous droplets and the leaf surfaces of 86 species from 25 genera. In the majority of cases a dense layer of overlapping, stellate or peltate trichomes held water off the leaf epidermis proper. In the case of hydrophobic tank-forming tillandsioideae, a powdery epicuticular wax layer provided water repellency. The irregular architecture of these indumenta resulted in relatively little contact with water droplets. Most mesic terrestrial Pitcairnioideae examined either possessed glabrous leaf blades or hydrophobic layers of confluent trichomes on the abaxial surface. Thus, the present study indicates that an important ancestral function of the foliar trichome in Bromeliaceae was water repellency. The ecophysiological consequences of hydrophobia are discussed.
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