title: Capacitive water release and internal leaf water relocation delay drought-induced cavitation in African Maesopsis eminii.
abstract: The impact of drought on the hydraulic functioning of important African tree species, like Maesopsis eminii Engl., is poorly understood. To map the hydraulic response to drought-induced cavitation, sole reliance on the water potential at which 50% loss of xylem hydraulic conductivity (ψ50) occurs might be limiting and at times misleading as the value alone does not give a comprehensive overview of strategies evoked by M. eminii to cope with drought. This article therefore uses a methodological framework to study the different aspects of drought-induced cavitation and water relations in M. eminii. Hydraulic functioning of whole-branch segments was investigated during bench-top dehydration. Cumulative acoustic emissions and continuous weight measurements were used to quantify M. eminii's vulnerability to drought-induced cavitation and hydraulic capacitance. Wood structural traits, including wood density, vessel area, diameter and wall thickness, vessel grouping index, solitary vessel index and vessel wall reinforcement, were used to underpin observed physiological responses. On average, M. eminii's ψ50 (±SE) was -1.9 ± 0.1 MPa, portraying its xylem as drought vulnerable, just as one would expect for a common tropical pioneer. However, M. eminii additionally employed an interesting desiccation delay strategy, fuelled by internal relocation of leaf water, hydraulic capacitance and the presence of parenchyma around the xylem vessels. Our findings suggest that exclusive dependence on ψ50 would have misdirected our assessments of M. eminii's drought stress vulnerability. Hydraulic capacitance linked to anatomy and leaf-water relocation behaviour was equally important to better understand M. eminii's drought survival strategies. Because our study was conducted on branches of 3-year-old greenhouse-grown M. eminii seedlings, the findings cannot be simply extrapolated to adult M. eminii trees or their mature wood, because structural and physiological plant properties change with age. The techniques and methodological framework used in this study are, however, transferable to other species regardless of age.
authors.affiliation: Laboratory of Plant Ecology, Department of Applied Ecology and Environmental Biology, Faculty of Bioscience Engineering, Ghent University, Coupure links 653, B-9000 Ghent, Belgium.|CAVElab Computational & Applied Vegetation Ecology, Department of Applied Ecology and Environmental Biology, Ghent University, Coupure links 653, B-9000 Ghent, Belgium.
authors.forename: Jackie
authors.initials: J
authors.lastname: Epila
authors.affiliation: Laboratory of Plant Ecology, Department of Applied Ecology and Environmental Biology, Faculty of Bioscience Engineering, Ghent University, Coupure links 653, B-9000Ghent, Belgium.
authors.forename: Niels J F
authors.initials: NJF
authors.lastname: De Baerdemaeker
authors.affiliation: Laboratory of Plant Ecology, Department of Applied Ecology and Environmental Biology, Faculty of Bioscience Engineering, Ghent University, Coupure links 653, B-9000Ghent, Belgium.
authors.forename: Lidewei L
authors.initials: LL
authors.lastname: Vergeynst
authors.affiliation: Laboratory of Plant Ecology, Department of Applied Ecology and Environmental Biology, Faculty of Bioscience Engineering, Ghent University, Coupure links 653, B-9000 Ghent, Belgium.|Remote Sensing, University of Technology Sydney (UTS), 745 Harris Str., Broadway 2007, NSW, Australia.
authors.forename: Wouter H
authors.initials: WH
authors.lastname: Maes
authors.affiliation: Laboratory for Wood Biology and Xylarium (Royal Museum for Central Africa), Leuvensesteenweg 13, B-3080 Tervuren, Belgium.
authors.forename: Hans
authors.initials: H
authors.lastname: Beeckman
authors.affiliation: Laboratory of Plant Ecology, Department of Applied Ecology and Environmental Biology, Faculty of Bioscience Engineering, Ghent University, Coupure links 653, B-9000Ghent, Belgium.
authors.forename: Kathy
authors.initials: K
authors.lastname: Steppe
mesh_terms: D055864:Droughts; D018515:Plant Leaves / Q000502:physiology*; D027823:Rhamnaceae / Q000502:physiology*; D014197:Trees / Q000502:physiology; D014867:Water / Q000502:physiology*; D052584:Xylem / Q000502:physiology
chemical_list: D014867:Water
keywords: acoustic emissions; anatomy; desiccation time; drought stress; embolism; hydraulic capacitance; tropical seedlings; vulnerability curve