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1. Increased adaxial stomatal density is associated with greater mesophyll surface area exposed to intercellular air spaces and mesophyll conductance in diverse C 4 grasses

   https://doi.org/10.1111/nph.16106  

   Pathare, Varsha S. ; Koteyeva, Nuria ; Cousins, Asaph B. ( September 2019 , New Phytologist)

   Mesophyll conductance (g_m) is the diffusion ofCO₂from intercellular air spaces (IAS) to the first site of carboxylation in the mesophyll cells. In C₃species,g_mis influenced by diverse leaf structural and anatomical traits; however, little is known about traits affectingg_min C₄species.

   To address this knowledge gap, we used online oxygen isotope discrimination measurements to estimateg_mand microscopy techniques to measure leaf structural and anatomical traits potentially related tog_min 18 C₄grasses.

   In this study,g_mscaled positively with photosynthesis and intrinsic water‐use efficiency (TE_i), but not with stomatal conductance. Also,g_mwas not determined by a single trait but was positively correlated with adaxial stomatal densities (SD_ada), stomatal ratio (SR), mesophyll surface area exposed toIAS(S_mes) and leaf thickness. However,g_mwas not related to abaxial stomatal densities (SD_aba) and mesophyll cell wall thickness (T_CW).

   Our study suggests that greaterSD_adaandSRincreasedg_mby increasingS_mesand creating additional parallel pathways forCO₂diffusion inside mesophyll cells. Thus,SD_ada,SRandS_mesare important determinants of C₄‐g_mand could be the target traits selected or modified for achieving greaterg_mandTE_iin C₄species.

    

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2. Using the rapid A‐C i response (RACiR) in the Li‐Cor 6400 to measure developmental gradients of photosynthetic capacity in poplar

   https://doi.org/10.1111/pce.13436  

   Lawrence, Erica H. ; Stinziano, Joseph R. ; Hanson, David T. ( October 2018 , Plant, Cell & Environment)

   The rapid A‐C_iresponse (RACiR) technique alleviates limitations of measuring photosynthetic capacity by reducing the time needed to determine the maximum carboxylation rate (V_cmax) and electron transport rate (J_max) in leaves. Photosynthetic capacity and its relationships with leaf development are important for understanding ecological and agricultural productivity; however, our current understanding is incomplete. Here, we show that RACiR can be used in previous generation gas exchange systems (i.e., the LI‐6400) and apply this method to rapidly investigate developmental gradients of photosynthetic capacity in poplar. We compared RACiR‐determined V_cmaxand J_maxas well as respiration and stomatal conductance (g_s) across four stages of leaf expansion inPopulus deltoidesand the poplar hybrid 717‐1B4 (Populus tremula × Populus alba). These physiological data were paired with leaf traits including nitrogen concentration, chlorophyll concentrations, and specific leaf area. Several traits displayed developmental trends that differed between the poplar species, demonstrating the utility of RACiR approaches to rapidly generate accurate measures of photosynthetic capacity. By using both new and old machines, we have shown how more investigators will be able to incorporate measurements of important photosynthetic traits in future studies and further our understanding of relationships between development and leaf‐level physiology.

    

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3. Contrasting ecosystem CO 2 fluxes of inland and coastal wetlands: a meta‐analysis of eddy covariance data

   https://doi.org/10.1111/gcb.13424  

   Lu, Weizhi ; Xiao, Jingfeng ; Liu, Fang ; Zhang, Yue ; Liu, Chang'an ; Lin, Guanghui ( August 2016 , Global Change Biology)

   Wetlands play an important role in regulating the atmospheric carbon dioxide (CO₂) concentrations and thus affecting the climate. However, there is still lack of quantitative evaluation of such a role across different wetland types, especially at the global scale. Here, we conducted a meta‐analysis to compare ecosystemCO₂fluxes among various types of wetlands using a global database compiled from the literature. This database consists of 143 site‐years of eddy covariance data from 22 inland wetland and 21 coastal wetland sites across the globe. Coastal wetlands had higher annual gross primary productivity (GPP), ecosystem respiration (R_e), and net ecosystem productivity (NEP) than inland wetlands. On a per unit area basis, coastal wetlands provided largeCO₂sinks, while inland wetlands provided smallCO₂sinks or were nearlyCO₂neutral. The annualCO₂sink strength was 93.15 and 208.37 g C m⁻²for inland and coastal wetlands, respectively. AnnualCO₂fluxes were mainly regulated by mean annual temperature (MAT) and mean annual precipitation (MAP). For coastal and inland wetlands combined,MATandMAPexplained 71%, 54%, and 57% of the variations inGPP,R_e, andNEP, respectively. TheCO₂fluxes of wetlands were also related to leaf area index (LAI). TheCO₂fluxes also varied with water table depth (WTD), although the effects ofWTDwere not statistically significant.NEPwas jointly determined byGPPandR_efor both inland and coastal wetlands. However, theNEP/R_eandNEP/GPPratios exhibited little variability for inland wetlands and decreased for coastal wetlands with increasing latitude. The contrasting ofCO₂fluxes between inland and coastal wetlands globally can improve our understanding of the roles of wetlands in the global C cycle. Our results also have implications for informing wetland management and climate change policymaking, for example, the efforts being made by international organizations and enterprises to restore coastal wetlands for enhancing blue carbon sinks.

    

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4. Thresholds for leaf damage due to dehydration: declines of hydraulic function, stomatal conductance and cellular integrity precede those for photochemistry

   https://doi.org/10.1111/nph.15779  

   Trueba, Santiago ; Pan, Ruihua ; Scoffoni, Christine ; John, Grace P. ; Davis, Stephen D. ; Sack, Lawren ( April 2019 , New Phytologist)

   Given increasing water deficits across numerous ecosystems world‐wide, it is urgent to understand the sequence of failure of leaf function during dehydration.

   We assessed dehydration‐induced losses of rehydration capacity and maximum quantum yield of the photosystemII(F_v/F_m) in the leaves of 10 diverse angiosperm species, and tested when these occurred relative to turgor loss, declines of stomatal conductanceg_s, and hydraulic conductanceK_leaf, including xylem and outside xylem pathways for the same study plants. We resolved the sequences of relative water content and leaf water potential Ψ_leafthresholds of functional impairment.

   On average, losses of leaf rehydration capacity occurred at dehydration beyond 50% declines ofg_s,K_leafand turgor loss point. Losses ofF_v/F_moccurred after much stronger dehydration and were not recovered with leaf rehydration. Across species, tissue dehydration thresholds were intercorrelated, suggesting trait co‐selection. Thresholds for each type of functional decline were much less variable across species in terms of relative water content than Ψ_leaf.

   The stomatal and leaf hydraulic systems show early functional declines before cell integrity is lost. Substantial damage to the photochemical apparatus occurs at extreme dehydration, after complete stomatal closure, and seems to be irreversible.

    

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5. Cultivated sunflower ( Helianthus annuus L.) has lower tolerance of moderate drought stress than its con‐specific wild relative, but the underlying traits remain elusive

   https://doi.org/10.1002/pld3.581  

   Tran, Vivian H. ; Nolting, Kristen M. ; Donovan, Lisa A. ; Temme, Andries A. ( April 2024 , Plant Direct)

   Cultivated crops are generally expected to have less abiotic stress tolerance than their wild relatives. However, this assumption is not well supported by empirical literature and may depend on the type of stress and how it is imposed, as well as the measure of tolerance being used. Here, we investigated whether wild and cultivated accessions ofHelianthus annuusdiffered in stress tolerance assessed as proportional decline in biomass due to drought and whether wild and cultivated accessions differed in trait responses to drought and trait associations with tolerance. In a greenhouse study,H. annuusaccessions in the two domestication classes (eight cultivated and eight wild accessions) received two treatments: a well‐watered control and a moderate drought implemented as a dry down followed by maintenance at a predetermined soil moisture level with automated irrigation. Treatments were imposed at the seedling stage, and plants were harvested after 2 weeks of treatment. The proportional biomass decline in response to drought was 24% for cultivatedH. annuusaccessions but was not significant for the wild accessions. Thus, using the metric of proportional biomass decline, the cultivated accessions had less drought tolerance. Among accessions, there was no tradeoff between drought tolerance and vigor assessed as biomass in the control treatment. In a multivariate analysis, wild and cultivated accessions did not differ from each other or in response to drought for a subset of morphological, physiological, and allocational traits. Analyzed individually, traits varied in response to drought in wild and/or cultivated accessions, including declines in specific leaf area, leaf theoretical maximum stomatal conductance (g_smax), and stomatal pore length, but there was no treatment response for stomatal density, succulence, or the ability to osmotically adjust. Focusing on traits associations with tolerance, plasticity in g_smaxwas the most interesting because its association with tolerance differed by domestication class (although the effects were relatively weak) and thus might contribute to lower tolerance of cultivated sunflower. OurH. annuusresults support the expectation that stress tolerance is lower in crops than wild relatives under some conditions. However, determining the key traits that underpin differences in moderate drought tolerance between wild and cultivatedH. annuusremains elusive.

    

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