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1. Leaf Hydraulic Architecture and Stomatal Conductance: A Functional Perspective

   https://doi.org/10.1104/pp.17.00303  

   Rockwell, Fulton E.; Holbrook, N. Michele (August 2017, Plant Physiology)
2. Detecting long‐term changes in stomatal conductance: challenges and opportunities of tree‐ring δ¹⁸O proxy

   https://doi.org/10.1111/nph.18430  

   Guerrieri, Rossella; Belmecheri, Soumaya; Asbjornsen, Heidi; Xiao, Jingfeng; Hollinger, David Y.; Clark, Kenneth; Jennings, Katie; Kolb, Thomas E.; Munger, J. William; Richardson, Andrew D.; et al (November 2022, New Phytologist)
3. Mechanisms for minimizing height‐related stomatal conductance declines in tall vines

   https://doi.org/10.1111/pce.13593  

   Domec, Jean‐Christophe; Berghoff, Henry; Way, Danielle A.; Moshelion, Menachem; Palmroth, Sari; Kets, Katre; Huang, Cheng‐Wei; Oren, Ram (June 2019, Plant, Cell & Environment)

   Abstract The ability to transport water through tall stems hydraulically limits stomatal conductance (g_s), thereby constraining photosynthesis and growth. However, some plants are able to minimize this height‐related decrease ing_s, regardless of path length. We hypothesized that kudzu (Pueraria lobata) prevents strong declines ing_swith height through appreciable structural and hydraulic compensative alterations. We observed only a 12% decline in maximumg_salong 15‐m‐long stems and were able to model this empirical trend. Increasing resistance with transport distance was not compensated by increasing sapwood‐to‐leaf‐area ratio. Compensating for increasing leaf area by adjusting the driving force would require water potential reaching −1.9 MPa, far below the wilting point (−1.2 MPa). The negative effect of stem length was compensated for by decreasing petiole hydraulic resistance and by increasing stem sapwood area and water storage, with capacitive discharge representing 8–12% of the water flux. In addition, large lateral (petiole, leaves) relative to axial hydraulic resistance helped improve water flow distribution to top leaves. These results indicate thatg_sof distal leaves can be similar to that of basal leaves, provided that resistance is highest in petioles, and sufficient amounts of water storage can be used to subsidize the transpiration stream. 

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4. Canopy Height and Climate Dryness Parsimoniously Explain Spatial Variation of Unstressed Stomatal Conductance

   https://doi.org/10.1029/2022GL099339  

   Liu, Yanlan; Flournoy, Olivia; Zhang, Quan; Novick, Kimberly_A; Koster, Randal_D; Konings, Alexandra_G (August 2022, Geophysical Research Letters)

   Abstract The spatio‐temporal variation of stomatal conductance directly regulates photosynthesis, water partitioning, and biosphere‐atmosphere interactions. While many studies have focused on stomatal response to stresses, the spatial variation of unstressed stomatal conductance remains poorly determined, and is usually characterized in land surface models (LSMs) simply based on plant functional type (PFT). Here, we derived unstressed stomatal conductance at the ecosystem‐scale using observations from 115 global FLUXNET sites. When aggregated by PFTs, the across‐PFT pattern was highly consistent with the parameterizations of LSMs. However, PFTs alone captured only 17% of the variation in unstressed stomatal conductance across sites. Within the same PFT, unstressed stomatal conductance was negatively related to climate dryness and canopy height, which explained 45% of the total spatial variation. Our results highlight the importance of plant‐environment interactions in shaping stomatal traits. The trait‐environment relationship established here provides an empirical approach for improved parameterizations of stomatal conductance in LSMs. 

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5. Disentangling the role of photosynthesis and stomatal conductance on rising forest water-use efficiency

   https://doi.org/10.1073/pnas.1905912116  

   Guerrieri, Rossella; Belmecheri, Soumaya; Ollinger, Scott V.; Asbjornsen, Heidi; Jennings, Katie; Xiao, Jingfeng; Stocker, Benjamin D.; Martin, Mary; Hollinger, David Y.; Bracho-Garrillo, Rosvel; et al (August 2019, Proceedings of the National Academy of Sciences)

   Multiple lines of evidence suggest that plant water-use efficiency (WUE)—the ratio of carbon assimilation to water loss—has increased in recent decades. Although rising atmospheric CO 2 has been proposed as the principal cause, the underlying physiological mechanisms are still being debated, and implications for the global water cycle remain uncertain. Here, we addressed this gap using 30-y tree ring records of carbon and oxygen isotope measurements and basal area increment from 12 species in 8 North American mature temperate forests. Our goal was to separate the contributions of enhanced photosynthesis and reduced stomatal conductance to WUE trends and to assess consistency between multiple commonly used methods for estimating WUE. Our results show that tree ring-derived estimates of increases in WUE are consistent with estimates from atmospheric measurements and predictions based on an optimal balancing of carbon gains and water costs, but are lower than those based on ecosystem-scale flux observations. Although both physiological mechanisms contributed to rising WUE, enhanced photosynthesis was widespread, while reductions in stomatal conductance were modest and restricted to species that experienced moisture limitations. This finding challenges the hypothesis that rising WUE in forests is primarily the result of widespread, CO 2 -induced reductions in stomatal conductance. 

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