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1. Transport in a coordinated soil-root-xylem-phloem leaf system

   https://doi.org/10.1016/j.advwatres.2018.06.002  

   Huang, Cheng-Wei; Domec, Jean-Christophe; Palmroth, Sari; Pockman, William T.; Litvak, Marcy E.; Katul, Gabriel G. (September 2018, Advances in Water Resources)
2. Transport in a coordinated soil-root-xylem-phloem leaf system

   https://doi.org/org/10.1016/j.advwatres.2018.06.002.06.002  

   Cheng-Wei, Huang; domec, Jean-Christophe; Palmroth, Sari; Pockman, William T.; Litvak, Marcy E; Katul, Gabriel G (September 2018, Advances in water resources)

   Links between the carbon and water economies of plants are coupled by combining the biochemical demand for atmospheric CO2 with gas transfer through stomates, liquid water transport in the soil-xylem hydraulic system and sucrose export in the phloem. We formulated a model to predict stomatal conductance (gs), consistent with the maximum energy circulation concept of Lotka and Odum, by maximizing the sucrose flux out of photosynthesizing leaves. The proposed modeling approach recovers all prior results derived from stomatal optimization theories and profit-maximization arguments for the xylem hydraulic system aimed at predicting gs. The novel features of this approach are its ability to 1) predict the price of losing water in carbon units using xylem and phloem properties (i.e., the marginal water use efficiency) and 2) explain why water molecules become more expensive to exchange for CO2 molecules when soil moisture becomes limiting or when plants acclimate to new elevated atmospheric CO2 concentration. On short time-scales (sub-daily), predicted gs under many environmental stimuli were consistent with measurements reported in the literature, including a general sensitivity of gs to vapor pressure deficit and leaf water potential. During progressive droughts, differences in the coordination among the leaf, xylem, and phloem functioning determine the isohydric-to-anisohydric behavior among plants. 

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3. Xylem functioning, dysfunction and repair: a physical perspective and implications for phloem transport

   https://doi.org/10.1093/treephys/tpy097  

   Konrad, Wilfried; Katul, Gabriel; Roth-Nebelsick, Anita; Jensen, Kaare H; Holtta, Teemu (October 2018, Tree Physiology)
4. Xylem–phloem hydraulic coupling explains multiple osmoregulatory responses to salt stress

   https://doi.org/10.1111/nph.16072  

   Perri, Saverio; Katul, Gabriel G.; Molini, Annalisa (June 2019, New Phytologist)
5. Limited effects of xylem anatomy on embolism resistance in cycad leaves

   Jiang, Guo-Feng; Qin, Bo-Tao; Pang, Yu-Kun; Qin, Lan-Li; Pereira, Luciano; Roddy, Adam B (July 2024, New phytologist)

   • Drought-induced xylem embolism is a primary cause of plant mortality. Although ~70% of cycads are threatened by extinction and extant cycads diversified during a period of increasing aridification, the vulnerability of cycads to embolism spread has been overlooked. • We quantified the vulnerability to drought-induced embolism, pressure-volume curves, in situ water potentials, and a suite of xylem anatomical traits of leaf pinnae and rachises for 20 cycad species. We tested whether anatomical traits were linked to hydraulic safety in cycads. • Compared to other major vascular plant clades, cycads exhibited similar embolism resistance to angiosperms and pteridophytes but were more vulnerable to embolism than non-cycad gymnosperms. All 20 cycads had both tracheids and vessels, the proportions of which were unrelated to embolism resistance. Only vessel pit membrane fraction was positively correlated to embolism resistance, contrary to angiosperms. Water potential at turgor loss was significantly correlated to embolism resistance among cycads. • Our results show that cycads exhibit low resistance to xylem embolism and that xylem anatomical traits–particularly vessels–may influence embolism resistance together with tracheids. This study highlights the importance of understanding the mechanisms of drought resistance in evolutionarily unique and threatened lineages like the cycads. 

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