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No gas source, no problem: pre-existing embolism may affect non-pressure driven embolism spreading in angiosperm xylem by gas diffusion
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  • Xinyi Guan,
  • Scott McAdam,
  • Kun-Fang Cao,
  • Steven Jansen
Xinyi Guan
Institute of Systematic Botany and Ecology, Ulm University,

Corresponding Author:[email protected]

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Agronomic Institute (IAC)
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Scott McAdam
Purdue University
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Kun-Fang Cao
State Key Laboratory for Conservation and Utilisation of Subtropical Agro-Bioresources, Guangxi University
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Steven Jansen
Institute of Systematic Botany and Ecology, Ulm University
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Embolism spreading in dehydrating angiosperm xylem is driven by gas movement between embolised and sap-filled conduits. Here, we examine how proximity to pre-existing embolism and hydraulic segmentation affect embolism propagation. Based on the optical method, we compared xylem embolism resistance between detached leaves and leaves attached to branches, and between intact leaves and leaves with minor veins cut (n = 6 species). Moreover, we directly compared the optical and pneumatic method on detached leaves. Embolism resistance of detached leaves was significantly lower than leaves attached to stems, except for two species with all vessels ending in their petioles. Cutting of minor veins showed embolism spreading in narrow vessels near the cuts prior to wide vessels in major veins. Moreover, embolism spreading between open and intact vessels occurred at largely similar xylem water potentials than embolism spreading between intact vessels, resulting in strong similarity between the optical and pneumatic method. We conclude that embolism spreading may depend on a direct connection to pre-existing embolism as gas source, is not exclusively pressure-driven, and indirectly related to conduit size. Hydraulic segmentation, however, can minimise embolism spreading due to confined and/or poorly interconnected conduits, which may increase hydraulic safety by slowing down gas diffusion.