Injury to the xylem and vascular cambium is proposed to explain mortality following low severity fires. These tissues have been assessed independently, but the relative significance of the xylem and cambium is still uncertain. The goal of this study is to evaluate the xylem dysfunction hypothesis and cambium necrosis hypothesis simultaneously. The hot dry conditions of a low severity fire were simulated in a drying oven, exposing Sequoia sempervirens (Lamb. ex D. Don) shoots to 70 and 100 °C for 6–60 min. Cambial viability was measured with Neutral Red stain and water transport capacity was assessed by calculating the loss of hydraulic conductivity. Vulnerability curves were also constructed to determine susceptibility to drought-induced embolism following heat exposure. The vascular cambium died completely at 100 °C after only 6 min of heat exposure, while cells remained viable at 70 °C temperatures for up to 15 min. Sixty minutes of exposure to 70 °C reduced stem hydraulic conductivity by 40%, while 45 min at 100 °C caused complete loss of conductivity. The heat treatments dropped hydraulic conductivity irrecoverably but did not significantly impact post-fire vulnerability to embolism. Overall, the damaging effects of high temperature occurred more rapidly in the vascular cambium than xylem following heat exposure. Importantly, the xylem remained functional until the most extreme treatments, long after the vascular cambium had died. Our results suggest that the viability of the vascular cambium may be more critical to post-fire survival than xylem function in S. sempervirens. Given the complexity of fire, we recommend ground-truthing the cambial and xylem post-fire response on a diverse range of species.
The young seedling life stage is critical for reforestation after disturbance and for species migration under climate change, yet little is known regarding their basic hydraulic function or vulnerability to drought. Here, we sought to characterize responses to desiccation including hydraulic vulnerability, xylem anatomical traits, and impacts on other stem tissues that contribute to hydraulic functioning.
In non‐stressed samples for all species, pith and cortical cells appeared circular and well hydrated, but they started to empty and deform with decreasing
- Award ID(s):
- 1656610
- NSF-PAR ID:
- 10454259
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- American Journal of Botany
- Volume:
- 107
- Issue:
- 8
- ISSN:
- 0002-9122
- Page Range / eLocation ID:
- p. 1177-1188
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract The coordination of plant leaf water potential (ΨL) regulation and xylem vulnerability to embolism is fundamental for understanding the tradeoffs between carbon uptake and risk of hydraulic damage. There is a general consensus that trees with vulnerable xylem more conservatively regulate ΨLthan plants with resistant xylem. We evaluated if this paradigm applied to three important eastern US temperate tree species,
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Premise Because of its broad range in the neotropical rainforest and within tree canopies, the tank bromeliad
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K leaf.Results After 7 d with no rain in the field or 14 days with no water in the glasshouse,
K leafdecreased by 50% yet increased to hydrated values within 4 d of tank refilling. Staining to detect embolism combined with modeling indicated that changes outside the xylem were of greater importance toK leafthan were changes inside the xylem and were associated with changes in intercellular air spaces (aerenchyma), aquaporin expression and inhibition, and cuticular conductance.Conclusions Low values for all conductances during drying, particularly in pathways outside the xylem, lead to hydraulic resilience for this species and may also contribute to its broad environmental tolerances.
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