Towards a statistically robust determination of minimum water potential and hydraulic risk in plants

Abstract

 Minimum water potential ( min ) is a key variable to characterize dehydration tolerance and hydraulic safety margins (HSM) in plants.  min is usually estimated as the absolute minimum tissue  experienced by a species, but this is problematic because sample extremes are affected by sample size and by the underlying probability distribution. We compare alternative approaches to estimate  min and assess the corresponding uncertainties and biases; propose statistically robust estimation methods based on extreme value theory (EVT); and assess the implications of our results for the characterization of hydraulic risk. Our results show that current estimates of  min and HSM are biased, as they are strongly affected by sample size. Because sampling effort is generally higher for species living in dry environments, the differences in current  min estimates between these species and those living under milder Accepted ArticleThis article is protected by copyright. All rights reserved conditions are partly artifactual. When this bias is corrected using EVT methods, resulting HSM tend to increase substantially with resistance to embolism across species. Although data availability and representativeness remain the main challenges for proper determination of  min , a closer look at  distributions and the use of statistically robust methods to estimate  min opens new ground for characterizing plant hydraulic risks.

Small and slow is safe: On the drought tolerance of tropical tree species

“…Here, we used TLP‐based HSM to explore how drought tolerance is associated with the other trait axes. This was because (1) Ψ min was less abundant than TLP in our dataset (Table 1), (2) Ψ min field data may be affected by sampling protocol (Martínez‐Vilalta et al, 2021) and (3) TLP‐based HSM recently proved to be highly indicative of observed drought‐induced mortality rates (Martin‐StPaul et al, 2017; Powers et al, 2020). However, we included Ψ min and Ψ min ‐based HSM in our exploration of how drought tolerance traits are coordinated.…”

Wood density and hydraulic traits influence species’ growth response to drought across biomes

“…At the same time, tracheid's formation is strongly influenced by Ψmin, as low pressures result in reduced cell expansion and thus lower lumen areas, increasing wood density. These relationships could explain the strength of the RWI‐SPEI relationship covariation with WD and Ψmin, although species‐level Ψmin values should be interpreted with caution (Martínez‐Vilalta et al, 2021). Ψmin is associated with atmospheric vapour pressure deficit, soil water potential, water use regulation and tree architecture (i.e.…”

Optimal balancing of xylem efficiency and safety explains plant vulnerability to drought

“…This bias could be related to an under-estimation of negative ψ min at wetter sites owing to lower sampling of rare dry days at such sites compared to more frequently occurring dry days at drier sites. Plants at wetter sites may be adapted to infrequent drought events which may be missed in the sampling of ψ min (Martinez Vilalta et al ., 2021).…”