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1. Larger diurnal temperature range undermined later autumn leaf senescence with warming in Europe

   https://doi.org/10.1111/geb.13674  

   Wang, Jian ; Liu, Desheng ( March 2023 , Global Ecology and Biogeography)

   Climate change regulates autumn leaf senescence date (LSD), exhibiting a strong phenological control of plant carbon uptake. Unlike the delaying effect of daily mean temperature (T_mean) on LSD, the impact of warming asymmetry in daytime and nighttime, as evidenced by variations of the diurnal temperature range (DTR), remains elusive. The objectives of this study were to investigate physiological and ecological impacts of DTR on LSD using long‐termin situobservations and to predict the future trends of LSD under warming.

   Europe.

   1950–2015.

   Plant phenology.

   We used partial correlation analysis, multiple linear regression and ridge regression to explore the impacts of DTR on LSD. To quantify the importance of potential drivers of LSD, we trained random forest models and applied the SHapley Additive exPlanations method to isolate the marginal contributions of each predictor on LSD. For LSD modelling and projection, we first evaluated two temperature‐driven LSD models [i.e., cooling‐degree‐day (CDD, without DTR effect) and day–night‐temperature CDD (DN_CDD, with DTR effect)], then applied them to predict future LSDs.

   We found that observational increases inT_meanand DTR had contrasting effects on LSD. IncreasedT_meandelayed the LSD, whereas larger DTR overall had an advancing effect. Considering the DTR effect, theT_meansensitivity of LSD was 14% lower than presently estimated (2.4 vs. 2.8 days °C⁻¹). Warming asymmetry‐related drought stress and plant functional traits (i.e., plant isohydricity and water‐use efficiency) potentially explained the advancing effect of DTR on LSD. We found that current projections of future LSD are overestimated because the DTR effect is discounted, suggesting the need for an adequate understanding of how plant phenology responds to warming asymmetry.

   Our findings highlight the importance of DTR in controlling LSD variations with an advancing‐dominant effect and call for the improvement of phenology modelling incorporating the DTR effect. Given that DTR showed a globally narrowing trend over the last several decades, more efforts are needed to understand the potential ecological impacts of warming asymmetry and vegetation response to climate change.

    

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2. Trading water for carbon in the future: Effects of elevated CO2 and warming on leaf hydraulic traits in a semiarid grassland

   https://doi.org/10.1111/gcb.16314  

   Mueller, Kevin E. ; Ocheltree, Troy W. ; Kray, Julie A. ; Bushey, Julie A. ; Blumenthal, Dana M. ; Williams, David G. ; Pendall, Elise ( August 2022 , Global Change Biology)

   The effects of climate change on plants and ecosystems are mediated by plant hydraulic traits, including interspecific and intraspecific variability of trait phenotypes. Yet, integrative and realistic studies of hydraulic traits and climate change are rare. In a semiarid grassland, we assessed the response of several plant hydraulic traits to elevated CO₂(+200 ppm) and warming (+1.5 to 3°C; day to night). For leaves of five dominant species (three graminoids and two forbs), and in replicated plots exposed to 7 years of elevated CO₂, warming, or ambient climate, we measured: stomatal density and size, xylem vessel size, turgor loss point, and water potential (pre‐dawn). Interspecific differences in hydraulic traits were larger than intraspecific shifts induced by elevated CO₂and/or warming. Effects of elevated CO₂were greater than effects of warming, and interactions between treatments were weak or not detected. The forbs showed little phenotypic plasticity. The graminoids had leaf water potentials and turgor loss points that were 10% to 50% less negative under elevated CO₂; thus, climate change might cause these species to adjust their drought resistance strategy away from tolerance and toward avoidance. The C4 grass also reduced allocation of leaf area to stomata under elevated CO₂, which helps explain observations of higher soil moisture. The shifts in hydraulic traits under elevated CO₂were not, however, simply due to higher soil moisture. Integration of our results with others' indicates that common species in this grassland are more likely to adjust stomatal aperture in response to near‐term climate change, rather than anatomical traits; this contrasts with apparent effects of changing CO₂on plant anatomy over evolutionary time. Future studies should assess how plant responses to drought may be constrained by the apparent shift from tolerance (via low turgor loss point) to avoidance (via stomatal regulation and/or access to deeper soil moisture).

    

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3. Characterizing the breakpoint of stomatal response to vapor pressure deficit in an angiosperm

   https://doi.org/10.1093/plphys/kiad560  

   Binstock, Benjamin R. ; Manandhar, Anju ; McAdam, Scott A. M. ( October 2023 , Plant Physiology)

   Vapor pressure difference between the leaf and atmosphere (VPD) is the most important regulator of daytime transpiration, yet the mechanism driving stomatal responses to an increase in VPD in angiosperms remains unresolved. Here, we sought to characterize the mechanism driving stomatal closure at high VPD in an angiosperm species, particularly testing whether abscisic acid (ABA) biosynthesis could explain the observation of a trigger point for stomatal sensitivity to an increase in VPD. We tracked leaf gas exchange and modeled leaf water potential (Ψl) in leaves exposed to a range of step-increases in VPD in the herbaceous species Senecio minimus Poir. (Asteraceae). We found that mild increases in VPD in this species did not induce stomatal closure because modeled Ψl did not decline below a threshold close to turgor loss point (Ψtlp), but when leaves were exposed to a large increase in VPD, stomata closed as modeled Ψl declined below Ψtlp. Leaf ABA levels were higher in leaves exposed to a step-increase in VPD that caused Ψl to transiently decline below Ψtlp and in which stomata closed compared with leaves in which stomata did not close. We conclude that the stomata of S. minimus are insensitive to VPD until Ψl declines to a threshold that triggers the biosynthesis of ABA and that this mechanism might be common to angiosperms.

    

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4. KARRIKIN UPREGULATED F-BOX 1 negatively regulates drought tolerance in Arabidopsis

   https://doi.org/10.1093/plphys/kiac336  

   Tian, Hongtao ; Watanabe, Yasuko ; Nguyen, Kien Huu ; Tran, Cuong Duy ; Abdelrahman, Mostafa ; Liang, Xiaohan ; Xu, Kun ; Sepulveda, Claudia ; Mostofa, Mohammad Golam ; Van Ha, Chien ; et al ( July 2022 , Plant Physiology)

   The karrikin (KAR) receptor and several related signaling components have been identified by forward genetic screening, but only a few studies have reported on upstream and downstream KAR signaling components and their roles in drought tolerance. Here, we characterized the functions of KAR UPREGULATED F-BOX 1 (KUF1) in drought tolerance using a reverse genetics approach in Arabidopsis (Arabidopsis thaliana). We observed that kuf1 mutant plants were more tolerant to drought stress than wild-type (WT) plants. To clarify the mechanisms by which KUF1 negatively regulates drought tolerance, we performed physiological, transcriptome, and morphological analyses. We found that kuf1 plants limited leaf water loss by reducing stomatal aperture and cuticular permeability. In addition, kuf1 plants showed increased sensitivity of stomatal closure, seed germination, primary root growth, and leaf senescence to abscisic acid (ABA). Genome-wide transcriptome comparisons of kuf1 and WT rosette leaves before and after dehydration showed that the differences in various drought tolerance-related traits were accompanied by differences in the expression of genes associated with stomatal closure (e.g. OPEN STOMATA 1), lipid and fatty acid metabolism (e.g. WAX ESTER SYNTHASE), and ABA responsiveness (e.g. ABA-RESPONSIVE ELEMENT 3). The kuf1 mutant plants had higher root/shoot ratios and root hair densities than WT plants, suggesting that they could absorb more water than WT plants. Together, these results demonstrate that KUF1 negatively regulates drought tolerance by modulating various physiological traits, morphological adjustments, and ABA responses and that the genetic manipulation of KUF1 in crops is a potential means of enhancing their drought tolerance.

    

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5. Use of hydraulic traits for modeling genotype‐specific acclimation in cotton under drought

   https://doi.org/10.1111/nph.16751  

   Wang, Diane R. ; Venturas, Martin D. ; Mackay, D. Scott ; Hunsaker, Douglas J. ; Thorp, Kelly R. ; Gore, Michael A. ; Pauli, Duke ( July 2020 , New Phytologist)

   Understanding the genetic and physiological basis of abiotic stress tolerance under field conditions is key to varietal crop improvement in the face of climate variability. Here, we investigate dynamic physiological responses to water stressin silicoand their relationships to genotypic variation in hydraulic traits of cotton (Gossypium hirsutum), an economically important species for renewable textile fiber production.

   In conjunction with an ecophysiological process‐based model, heterogeneous data (plant hydraulic traits, spatially‐distributed soil texture, soil water content and canopy temperature) were used to examine hydraulic characteristics of cotton, evaluate their consequences on whole plant performance under drought, and explore potential genotype × environment effects.

   Cotton was found to have R‐shaped hydraulic vulnerability curves (VCs), which were consistent under drought stress initiated at flowering. Stem VCs, expressed as percent loss of conductivity, differed across genotypes, whereas root VCs did not. Simulation results demonstrated how plant physiological stress can depend on the interaction between soil properties and irrigation management, which in turn affect genotypic rankings of transpiration in a time‐dependent manner.

   Our study shows how a process‐based modeling framework can be used to link genotypic variation in hydraulic traits to differential acclimating behaviors under drought.

    

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