title: Rhizophoraceae Mangrove Saplings Use Hypocotyl and Leaf Water Storage Capacity to Cope with Soil Water Salinity Changes.
abstract: Some of the most striking features of Rhizophoraceae mangrove saplings are their voluminous cylinder-shaped hypocotyls and thickened leaves. The hypocotyls are known to serve as floats during seed dispersal (hydrochory) and store nutrients that allow the seedling to root and settle. In this study we investigate to what degree the hypocotyls and leaves can serve as water reservoirs once seedlings have settled, helping the plant to buffer the rapid water potential changes that are typical for the mangrove environment. We exposed saplings of two Rhizophoraceae species to three levels of salinity (15, 30, and 0-5‰, in that sequence) while non-invasively monitoring changes in hypocotyl and leaf water content by means of mobile NMR sensors. As a proxy for water content, changes in hypocotyl diameter and leaf thickness were monitored by means of dendrometers. Hypocotyl diameter variations were also monitored in the field on a Rhizophora species. The saplings were able to buffer rapid rhizosphere salinity changes using water stored in hypocotyls and leaves, but the largest water storage capacity was found in the leaves. We conclude that in Rhizophora and Bruguiera the hypocotyl offers the bulk of water buffering capacity during the dispersal phase and directly after settlement when only few leaves are present. As saplings develop more leaves, the significance of the leaves as a water storage organ becomes larger than that of the hypocotyl.
authors.affiliation: Department of Territorio e Sistemi Agro-Forestali, University of Padova, PadovaItaly; Laboratory of Plant Biology and Nature Management, Department of Biology, Vrije Universiteit Brussel, BrusselsBelgium.
authors.forename: Silvia
authors.initials: S
authors.lastname: Lechthaler
authors.affiliation: Laboratory of Plant Biology and Nature Management, Department of Biology, Vrije Universiteit Brussel, BrusselsBelgium; Laboratory of Wood Biology and Xylarium, Department of Wood Biology, Royal Museum for Central AfricaTervuren, Belgium.
authors.forename: Elisabeth M R
authors.initials: EM
authors.lastname: Robert
authors.affiliation: Laboratory of Plant Biology and Nature Management, Department of Biology, Vrije Universiteit Brussel, BrusselsBelgium; Laboratory of Wood Biology and Xylarium, Department of Wood Biology, Royal Museum for Central AfricaTervuren, Belgium.
authors.forename: Nathalie
authors.initials: N
authors.lastname: Tonné
authors.affiliation: Laboratory of Biophysics and Wageningen NMR Centre, Department of Agrotechnology & Food Sciences, Wageningen University, Wageningen Netherlands.
authors.forename: Alena
authors.initials: A
authors.lastname: Prusova
authors.affiliation: Laboratory of Biophysics and Wageningen NMR Centre, Department of Agrotechnology & Food Sciences, Wageningen University, Wageningen Netherlands.
authors.forename: Edo
authors.initials: E
authors.lastname: Gerkema
authors.affiliation: Laboratory of Biophysics and Wageningen NMR Centre, Department of Agrotechnology & Food Sciences, Wageningen University, Wageningen Netherlands.
authors.forename: Henk
authors.initials: H
authors.lastname: Van As
authors.affiliation: Laboratory of Plant Biology and Nature Management, Department of Biology, Vrije Universiteit Brussel, Brussels Belgium.
authors.forename: Nico
authors.initials: N
authors.lastname: Koedam
authors.affiliation: IBG-2: Plant Sciences, Institute for Bio- and Geosciences, Forschungszentrum Jülich, Jülich Germany.
authors.forename: Carel W
authors.initials: CW
authors.lastname: Windt
keywords: dendrometers; leaf thickness variations; magnetic resonance imaging (MRI); mangrove environment; mobile nuclear magnetic resonance (NMR)