Interspecific variability in physiological thresholds during dehydration reveals contrasting drought-response strategies and vulnerability to hydraulic failure in rainforest tree saplings

International audienceBackground - Several traits, mostly related to stomatal and xylem functioning, represent key mechanisms influencing specie’s survival during drought. However, little is known on their coordination, how they shape plant drought-response strategies and how important they are for survival, especially in tropical rainforest trees. Moreover, much focus has been made on hydraulic traits related to the ability of trees to avoid reaching critical levels of xylem embolism, since hydraulic failure is regarded as a ubiquitous process leading to drought-induced mortality. For this reason, less attention has been drawn to the potential simultaneous role of non-structural carbohydrates (NSC), which could get depleted during drought (i.e., carbon starvation) and help maintain osmoregulation. In fact, no study has satisfactorily investigated the joint response of the loss in xylem hydraulic conductance together with the use and eventual depletion of NSC for tropical rainforest species.Objectives - (i) Characterize the diversity of drought-response strategies of 12 coexisting rainforest tree species, (ii) evaluate if species drought-response strategies determine the prevalence of non-structural carbohydrate depletion during drought-induced hydraulic failure, (iii) identify the single or combined effects of traits implicated in species’ survival during drought.Methods - We studied saplings of 12 species of rainforest tree species in a shadehouse experiment. (i) We measured leaf turgor loss point, leaf and stem xylem vulnerability to embolism, lethal levels of water potentials and associated losses in hydraulic conductance causing mortality, as well as minimum leaf conductance. (ii) We investigated the joint response of the loss in leaf and stem xylem hydraulic conductance together with the response of starch and soluble sugar contents in leaves, stems and roots during a severe drought. (iii) We applied a mechanistic model computing time to hydraulic failure.Results and ImplicationsThis talk summarizes the main findings of this study regarding plant functioning during drought, underlining specificities in plant drought-survival across tropical rainforest tree species and discussing the physiological mechanisms potentially involved in changes in tropical rainforest tree communities in a changing climate