DOI: 10.5061/dryad.hj0005k
title: Data from: Testing the divergent adaptation of two congeneric tree species on a rainfall gradient using eco-physio-morphological traits

description: In tropical Africa, evidence of widely distributed genera transcending
 biomes or habitat boundaries has been reported. The evolutionary processes
 that allowed these lineages to disperse and adapt into new environments
 are far from being resolved. To better understand these processes, we
 propose an integrated approach, based on the eco-physio-morphological
 traits of two sister species with adjacent distributions along a rainfall
 gradient. We used wood anatomical traits, plant hydraulics (vulnerability
 to cavitation, wood volumetric water content and hydraulic capacitance)
 and growth data from the natural habitat, in a common garden, to compare
 species with known phylogeny, very similar morphologically, but occupying
 contrasting habitats: Erythrophleum ivorense (wet forest) and
 Erythrophleum suaveolens (moist forest and forest gallery). We identified
 some slight differences in wood anatomical traits between the two species
 associated with strong differences in hydraulics, growth, and overall
 species distribution. The moist forest species, E. suaveolens had narrower
 vessels and intervessel pits, and higher vessel cell-wall reinforcement
 than E. ivorense. These traits allow a high resistance to cavitation and a
 continuous internal water supply of the xylem during water shortage,
 allowing a higher fitness during drought periods, but limiting growth. Our
 results confirm a trade-off between drought tolerance and growth,
 controlled by subtle adaptations in wood traits, as a key mechanism
 leading to the niche partitioning between the two Erythrophleum species.
 The generality of this trade-off and its importance in the diversification
 of the African tree flora remains to be tested. Our integrated
 eco-physio-morpho approach could be the way forward.
description: AE_WP_ErythrophleumCollected AE signals and water potential used to construct an acoustic vulnerability curves for E. ivorense ansd E. suaveolens. The AE signals were cumulated over the measurement period, and averaged over 5 minutes. The endpoint of the VCAE was based on the local maximum in the third derivative, following the strongest decrease in the first derivative. Cumulative acoustic emissions were then rescaled between zero and the defined endpoint to obtain a relative percentage of cavitation-related AE (%). The continuous water potential x-axis of the VCAE was obtained from a segmented linear regression relation between point measurements of xylem water potential, and xylem shrinkage monitored by dendrometers.wood_traits_ErythrophleumTangential vessel diameter, vessel density, vessel grouping index (ratio of total number of vessels to total number of vessel groupings), proportion of vessel lumen, fibre, axial and radial parenchyma measured for the two species, E. ivorense and E. suaveolens, in their natural habitat (branch and stem samples) and in a common garden experiement (only branch samples). On branch sections, these measurements were done on 0.16 mm² quadrats systematically distributed from the pith to the bark (from [0;400] to [2800;3200]), in order to include radial variation in wood traits. For stem sections, measurements were done on two quadrats of 9.40 mm². Intervessel wall thickness and fiber wall thickness (measured as the double wall between two adjacent fibers) were also measured at higher magnification. Conduit wall reinforcement was calculated by determining the wall thickness (t) to conduit wall span (b) ratio . On tangential sections, we measured the horizontal pit membrane diameter at its widest point but only for branch samples from natural habitat.growth_common_gardenGrowth in diameter in the common garden experiement for E. ivorense and E. suaveolens.growth_natural_habitatGrowth in diameter and diameter classes for the two species E. suaveolens and E. ivorense in their respective natural habitat.growthnatural_habitat.csv