Large hydraulic safety margins protect Neotropical canopy rainforest tree species against hydraulic failure during drought

Key message Abundant Neotropical canopy-tree species are more resistant to drought-induced branch embolism than what is currently admitted. Large hydraulic safety margins protect them from hydraulic failure under actual drought conditions.
Context Xylem vulnerability to embolism, which is associated to survival under extreme drought conditions, is being increasingly studied in the tropics, but data on the risk of hydraulic failure for lowland Neotropical rainforest canopy-tree species, thought to be highly vulnerable, are lacking.
Aims The purpose of this study was to gain more knowledge on species drought-resistance characteristics in branches and leaves and the risk of hydraulic failure of abundant rainforest canopy-tree species during the dry season.
Methods We first assessed the range of branch xylem vulnerability to embolism using the flow-centrifuge technique on 1-m-long sun-exposed branches and evaluated hydraulic safety margins with leaf turgor loss point and midday water potential during normal- and severe-intensity dry seasons for a large set of Amazonian rainforest canopy-tree species.
Results Tree species exhibited a broad range of embolism resistance, with the pressure threshold inducing 50% loss of branch hydraulic conductivity varying from − 1.86 to − 7.63 MPa. Conversely, we found low variability in leaf turgor loss point and dry season midday leaf water potential, and mostly large, positive hydraulic safety margins.
Conclusions Rainforest canopy-tree species growing under elevated mean annual precipitation can have high resistance to embolism and are more resistant than what was previously thought. Thanks to early leaf turgor loss and high embolism resistance, most species have a low risk of hydraulic failure and are well able to withstand normal and even severe dry seasons.

Keywords
Amazon rainforest, Embolism resistance, Hydraulic safety margins, Turgor loss point, Water potential

Open-Access Publication
Ziegler, C., Coste, S., Stahl, C. et al. Annals of Forest Science (2019) 76: 115. https://doi.org/10.1007/s13595-019-0905-0

Data availability
All data corresponding to species’ mean trait values are included in this published article (and its supplementary information files). All raw data generated during the current study are not publicly available at the moment because the authors of the study wish to keep them for further analysis. They will then be made public on an online repository. In the meantime, they can nonetheless be made available by the corresponding author on request.

Related blog post:
Highlighted paper of 2019 : C. Ziegler et al., “Large hydraulic safety margins protect Neotropical canopy rainforest tree species against hydraulic failure during drought”

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