Evidence of combined flower thermal and drought vulnerabilities portends reproductive failure under hotter-drought conditions.

Despite the abundant evidence of impairments to plant performance and survival under hotter-drought conditions, little is known about the vulnerability of reproductive organs to climate extremes. Here, by conducting a comparative analysis between flowers and leaves, we investigated how variations in key morphophysiological traits related to carbon and water economics can explain the differential vulnerabilities to heat and drought among these functionally diverse organs. Due to their lower construction costs, despite having a higher water storage capacity, flowers were more prone to turgor loss (higher turgor loss point; ΨTLP) than leaves, thus evidencing a trade-off between carbon investment and drought tolerance in reproductive organs. Importantly, the higher ΨTLP of flowers also resulted in narrow turgor safety margins (TSM). Moreover, compared to leaves, the cuticle of flowers had an overall higher thermal vulnerability, which also resulted in low leakage safety margins (LSM). As a result, the combination of low TSMs and LSMs may have negative impacts on reproduction success since they strongly influenced the time to turgor loss under simulated hotter-drought conditions. Overall, our results improve the knowledge of unexplored aspects of flower structure and function and highlight likely threats to successful plant reproduction in a warmer and drier world.

A bitter future for coffee production? Physiological traits associated with yield reveal high vulnerability to hydraulic failure in Coffea canephora.

The increase in frequency and intensity of drought events have hampered coffee production in the already threatened Amazon region, yet little is known about key aspects underlying the variability in yield potential across genotypes, nor to what extent higher productivity is linked to reduced drought tolerance. Here we explored how variations in morphoanatomical and physiological leaf traits can explain differences in yield and vulnerability to embolism in 11 Coffea canephora genotypes cultivated in the Western Amazon. The remarkable variation in coffee yield across genotypes was tightly related to differences in their carbon assimilation and water transport capacities, revealing a diffusive limitation to photosynthesis linked by hydraulic constraints. Although a clear trade-off between water transport efficiency and safety was not detected, all the studied genotypes operated in a narrow and/or negative hydraulic safety margin, suggesting a high vulnerability to leaf hydraulic failure (HF), especially on the most productive genotypes. Modelling exercises revealed that variations in HF across genotypes were mainly associated with differences in leaf water vapour leakage when stomata are closed, reflecting contrasting growth strategies. Overall, our results provide a new perspective on the challenges of sustaining coffee production in the Amazon region under a drier and warmer climate.

Metabolic shifts during fruit development in pungent and non-pungent peppers.

Fruit pungency is caused by the accumulation of capsaicinoids, secondary metabolites whose relation to primary metabolism remains unclear. We have selected ten geographically diverse accessions of Capsicum chinense Jacq with different pungency levels. A detailed metabolic profile was conducted in the fruit placenta and pericarp at 20, 45, and 60 days after anthesis aiming at increasing our understanding of the metabolic changes in these tissues across fruit development and their potential connection to capsaicin metabolism. Overall, despite the variation in fruit pungency among the ten accessions, the composition and metabolite levels in both placenta and pericarp were uniformly stable across accessions. Most of the metabolite variability occurred between the fruit developmental stages rather than among the accessions. Interestingly, different metabolite adjustments in the placenta were observed among pungent and non-pungent accessions, which seem to be related to differences in the genetic background. Furthermore, we observed high coordination between metabolites and capsaicin production in C. chinense fruits, suggesting that pungency in placenta is adjusted with primary metabolism.

Acclimation of hydraulic and morphological traits to water deficit delays hydraulic failure during simulated drought in poplar.

The capacity of trees to tolerate and survive increasing drought conditions in situ will depend in part on their ability to acclimate (via phenotypic plasticity) key hydraulic and morphological traits that increase drought tolerance and delay the onset of drought-induced hydraulic failure. However, the effect of water-deficit acclimation in key traits that determine time to hydraulic failure (THF) during extreme drought remains largely untested. We measured key hydraulic and morphological traits in saplings of a hybrid poplar grown under well-watered and water-limited conditions. The time for plants to dry-down to critical levels of water stress (90% loss of stem hydraulic conductance), as well as the relative contribution of drought acclimation in each trait to THF, was simulated using a soil-plant hydraulic model (SurEau). Compared with controls, water-limited plants exhibited significantly lower stem hydraulic vulnerability (P50stem), stomatal conductance and total canopy leaf area (LA). Taken together, adjustments in these and other traits resulted in longer modelled THF in water-limited (~160 h) compared with well-watered plants (~50 h), representing an increase of more than 200%. Sensitivity analysis revealed that adjustment in P50stem and LA contributed the most to longer THF in water-limited plants. We observed a high degree of trait plasticity in poplar saplings in response to water-deficit growth conditions, with decreases in stem hydraulic vulnerability and leaf area playing a key role in delaying the onset of hydraulic failure during a simulated drought event. These findings suggest that understanding the capacity of plants to acclimate to antecedent growth conditions will enable better predictions of plant survivorship during future drought.

Where do leaf water leaks come from? Trade-offs underlying the variability in minimum conductance across tropical savanna species with contrasting growth strategies.

Plants continue to lose water from their leaves even after complete stomatal closure. Although this minimum conductance (gleaf-res ) has substantial impacts on strategies of water use and conservation, little is known about the potential drivers underlying the variability of this trait across species. We thus untangled the relative contribution of water leaks from the cuticle and stomata in order to investigate how the variability in leaf morphological and anatomical traits is related to the variation in gleaf-res and carbon assimilation capacity across 30 diverse species from the Brazilian Cerrado. In addition to cuticle permeance, water leaks from stomata had a significant impact on gleaf-res . The differential pattern of stomata distribution in the epidermis was a key factor driving this variation, suggesting the existence of a trade-off between carbon assimilation and water loss through gleaf-res . For instance, higher gleaf-res , observed in fast-growing species, was associated with the investment in small and numerous stomata, which allowed higher carbon assimilation rates but also increased water leaks, with negative impacts on leaf survival under drought. Variation in cuticle structural properties was not linked to gleaf-res . Our results therefore suggest the existence of a trade-off between carbon assimilation efficiency and dehydration tolerance at foliar level.

Different ways to die in a changing world: Consequences of climate change for tree species performance and survival through an ecophysiological perspective.

Anthropogenic activities such as uncontrolled deforestation and increasing greenhouse gas emissions are responsible for triggering a series of environmental imbalances that affect the Earth's complex climate dynamics. As a consequence of these changes, several climate models forecast an intensification of extreme weather events over the upcoming decades, including heat waves and increasingly severe drought and flood episodes. The occurrence of such extreme weather will prompt profound changes in several plant communities, resulting in massive forest dieback events that can trigger a massive loss of biodiversity in several biomes worldwide. Despite the gravity of the situation, our knowledge regarding how extreme weather events can undermine the performance, survival, and distribution of forest species remains very fragmented. Therefore, the present review aimed to provide a broad and integrated perspective of the main biochemical, physiological, and morpho-anatomical disorders that may compromise the performance and survival of forest species exposed to climate change factors, particularly drought, flooding, and global warming. In addition, we also discuss the controversial effects of high CO2 concentrations in enhancing plant growth and reducing the deleterious effects of some extreme climatic events. We conclude with a discussion about the possible effects that the factors associated with the climate change might have on species distribution and forest composition.

A Structure Shaped by Fire, but Also Water: Ecological Consequences of the Variability in Bark Properties Across 31 Species From the Brazilian Cerrado.

Bark is a structure involved in multiple physiological functions, but which has been traditionally associated with protection against fire. Thus, little is known about how the morpho-anatomical variations of this structure are related to different ecological pressures, especially in tropical savanna species, which are commonly subjected to frequent fire and drought events. Here we evaluated how the structural and functional variations of bark are related to the processes of resilience and resistance to fire, as well as transport and storage of water in 31 native species from the Brazilian Cerrado. Because of their thick bark, none of the trees analyzed were top-killed after a severe fire event. The structural and functional variations of the bark were also associated with water storage and transport, functions related to properties of the inner bark. In fact, species with a thicker and less dense inner bark were the ones that had the highest water contents in the wood, bark, and leaves. Lower bark density was also related to higher stem hydraulic conductivity, carbon assimilation, and growth. Overall, we provide strong evidence that in addition to protection from fire, the relative investment in bark also reflects different strategies of water use and conservation among many Cerrado tree species.

Photosynthesis impairments and excitation energy dissipation on wheat plants supplied with silicon and infected with Pyricularia oryzae.

Considering the effect of silicon (Si) in reducing the blast symptoms on wheat in a scenario where the losses in the photosynthetic capacity of the infected plants is lowered, this study investigated the ability of using the incident light, the chloroplastidic pigments (chlorophylls and carotenoids) alterations and the possible role of carotenoids on the process of light dissipation on wheat plants non-supplied (-Si) or supplied (+Si) with Si and inoculated or not with Pyricularia oryzae. For + Si plants, blast severity was reduced compared to -Si plants. Reductions in the concentration of photosynthetic pigments (total chlorophyll, violanxanthin + antheraxanthin + zeaxanthin, ß-carotene and lutein) were greater for inoculated -Si plants than for inoculated + Si ones. The α-carotene concentration increased for inoculated -Si and +Si plants in comparison to non-inoculated plants limiting, therefore, lutein production. Higher functional damage to the photosystem II (PSII) was noticed for inoculated -Si plants with reductions in the values of maximum quantum quenching, photochemical yield of PSII and electron transport rate, but higher values for quenching non-photochemical. This finding also contributed to reductions in the values of light saturated rate photosynthesis and light saturation point for -Si plants which was attenuated for inoculated + Si plants. Increase in dark respiration values occurred for inoculated plants than for non-inoculated ones. The Si supply to wheat plants, besides reducing blast severity, contributed to their better photosynthetic performance. Moreover, inoculated + Si plants coped with drastic losses of light energy dissipation processes (fluorescence and heat) by increasing the concentration of carotenoids which helped to maintain the structural and functional viability of the photosynthetic machinery minimizing, therefore, lipid peroxidation and the production of reactive oxygen species.