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Abstract Drought events may increase the likelihood that the plant water transport system becomes interrupted by embolism. Yet our knowledge about the temporal frequency of xylem embolism in the field is frequently lacking, as it requires detailed, long‐term measurements.We measured xylem embolism resistance and midday xylem water potentials during the consecutive summers of 2019 and 2020 to estimate maximum levels of embolism in leaf and stem xylem of ten temperate angiosperm tree species. We also studied vessel and pit membrane characteristics based on light and electron microscopy to corroborate potential differences in embolism resistance between leaves and stems.Apart fromA.pseudoplatanusandQ.petraea, eight species experienced minimum xylem water potentials that were close to or below those required to initiate embolism. Water potentials corresponding to ca. 12% loss of hydraulic conductivity (PLC) could occur in six species, while considerable levels of embolism around 50% PLC were limited toB.pendulaandC.avellana. There was a general agreement in embolism resistance between stems and leaves, with leaves being equally or more resistant than stems. Also, xylem embolism resistance was significantly correlated to intervessel pit membrane thickness (TPM) for stems, but not to vessel diameter and total intervessel pit membrane surface area of a vessel.Our data indicate that low amounts of embolism occur in most species during moderate summer drought, and that considerable levels of embolism are uncommon. Moreover, our experimental andTPMdata show that leaf xylem is generally no more vulnerable than stem xylem.
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Mechanisms for minimizing height‐related stomatal conductance declines in tall vines
Abstract The ability to transport water through tall stems hydraulically limits stomatal conductance (gs), thereby constraining photosynthesis and growth. However, some plants are able to minimize this height‐related decrease ings, regardless of path length. We hypothesized that kudzu (Pueraria lobata) prevents strong declines ingswith height through appreciable structural and hydraulic compensative alterations. We observed only a 12% decline in maximumgsalong 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 thatgsof 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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- Award ID(s):
- 1754893
- PAR ID:
- 10455773
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Plant, Cell & Environment
- Volume:
- 42
- Issue:
- 11
- ISSN:
- 0140-7791
- Page Range / eLocation ID:
- p. 3121-3139
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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