Death from hunger or thirst? Phloem death, rather than xylem hydraulic failure, as a driver of fire‐induced conifer mortality

Summary Disruption of photosynthesis and carbon transport due to damage to the tree crown and stem cambial cells, respectively, can cause tree mortality. It has recently been proposed that fire‐induced dysfunction of xylem plays an important role in tree mortality. Here, we simultaneously tested the...

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Published in:The New phytologist 2023-02, Vol.237 (4), p.1154-1163
Main Authors: Partelli‐Feltrin, Raquel, Smith, Alistair M. S., Adams, Henry D., Thompson, R. Alex, Kolden, Crystal A., Yedinak, Kara M., Johnson, Daniel M.
Format: Article
Language:English
Subjects:
cambium
Carbohydrates
cavitation
Coniferous trees
Conifers
Death
Deformation
Fires
Fluid flow
Hunger
Hydraulics
Lethal dose
Mortality
Necrosis
nonstructural carbohydrates
Phloem
Photosynthesis
Pine needles
Pine trees
Pinus ponderosa
Plant Stems
Roots
Stems
Thirst
Transport
tree mortality
Trees - physiology
Water
Water transport
wildfires
Xylem
Xylem - physiology
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Summary:Summary Disruption of photosynthesis and carbon transport due to damage to the tree crown and stem cambial cells, respectively, can cause tree mortality. It has recently been proposed that fire‐induced dysfunction of xylem plays an important role in tree mortality. Here, we simultaneously tested the impact of a lethal fire dose on nonstructural carbohydrates (NSCs) and xylem hydraulics in Pinus ponderosa saplings. Saplings were burned with a known lethal fire dose. Nonstructural carbohydrates were assessed in needles, main stems, roots and whole plants, and xylem hydraulic conductivity was measured in the main stems up to 29 d postfire. Photosynthesis and whole plant NSCs declined postfire. Additionally, all burned saplings showed 100% phloem/cambium necrosis, and roots of burned saplings had reduced NSCs compared to unburned and defoliated saplings. We further show that, contrary to patterns observed with NSCs, water transport was unchanged by fire and there was no evidence of xylem deformation in saplings that experienced a lethal dose of heat from fire. We conclude that phloem and cambium mortality, and not hydraulic failure, were probably the causes of death in these saplings. These findings advance our understanding of the physiological response to fire‐induced injuries in conifer trees.
ISSN:0028-646X
1469-8137
DOI:10.1111/nph.18454