Abstract
Key messageAbundant 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.ContextXylem 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.AimsThe 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.MethodsWe 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.ResultsTree 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.ConclusionsRainforest 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.
Highlights
Tropical rainforest ecosystems are characterized by high annual rainfall
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
Vulnerability curves yielded embolism resistance parameters that varied strongly along a continuum across the studied species: Ψ12 varied from − 0.99 to − 6.78 MPa, Ψ50 varied from − 1.86 to − 7.63 MPa, Ψ88 varied from − 2.55 to − 10.22 MPa (F > 9; p < 0.001; Fig. 1, Table 1; Table 5, Fig. 5 and Fig. 6 in the Appendices) and ax varied from 21 to 240 %MPa−1 (Table 5 in the Appendices)
Summary
Tropical rainforest ecosystems are characterized by high annual rainfall. Yet, most Amazonian rainforests are regularly exposed to seasonal droughts due to the latitudinal movements of the Intertropical Convergence Zone (Bonal et al 2016). Reduced soil water availability due to low precipitation during the dry season can cause a reduction in tree growth (Wagner et al 2012), photosynthetic assimilation, and whole-tree transpiration due to stomatal closure (Stahl et al 2013). Increased mortality can occur with increasingly severe dry seasons (Phillips et al 2010) and species exhibiting contrasting drought-resistance characteristics are likely to be affected differently (Anderegg et al 2016). This indicates that drought resistance may provide an advantage for tropical trees under climate change and that droughts are likely to alter tree species’ distribution as well as community composition and functioning (Esquivel-Muelbert et al 2019). Little is known about the trait syndromes that confer drought resistance in tropical rainforests or how they participate in shaping species distribution along macro-environmental gradients of water availability (Zhu et al 2018)
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