Scaling of petiole anatomies, mechanics and vasculatures with leaf size in the widespread Neotropical pioneer tree species Cecropia obtusa Trécul (Urticaceae).

Patrick Heuret,Clément Stahl,Sabrina Coste,Sébastien Levionnois,Annikki Mäkelä,Hélène Morel,Eric Nicolini

doi:10.1093/treephys/tpz136

Abstract

Although the leaf economic spectrum has deepened our understanding of leaf trait variability, little is known about how leaf traits scale with leaf area. This uncertainty has resulted in the assumption that leaf traits should vary by keeping the same pace of variation with increases in leaf area across the leaf size range. We evaluated the scaling of morphological, tissue-surface and vascular traits with overall leaf area, and the functional significance of such scaling. We examined 1,271 leaves for morphological traits, and 124 leaves for anatomical and hydraulic traits, from 38 trees of Cecropia obtusa Trécul (Urticaceae) in French Guiana. Cecropia is a Neotropical genus of pioneer trees that can exhibit large laminas (0.4m2 for C. obtusa), with leaf size ranging by two orders of magnitude. We measured (i) tissue fractions within petioles and their second moment of area, (ii) theoretical xylem hydraulic efficiency of petioles and (iii) the extent of leaf vessel widening within the hydraulic path. We found that different scaling of morphological trait variability allows for optimisation of lamina display among larger leaves, especially the positive allometric relationship between lamina area and petiole cross-sectional area. Increasing the fraction of pith is a key factor that increases the geometrical effect of supportive tissues on mechanical rigidity and thereby increases carbon-use efficiency. We found that increasing xylem hydraulic efficiency with vessel size results in lower leaf lamina area: xylem ratios, which also results in potential carbon savings for large leaves. We found that the vessel widening is consistent with hydraulic optimisation models. Leaf size variability modifies scaling of leaf traits in this large-leaved species.

Highlights

The leaf economic spectrum has deepened our understanding of leaf trait variability, little is known about how leaf traits scale with leaf area
We found that increasing xylem hydraulic efficiency with vessel size results in lower leaf lamina area: xylem ratios, which results in potential carbon savings for large leaves
The different functional attributes linking flexural stiffness, carbon cost, and vasculature between large and small leaves, suggest that these three functional dimension –mechanics, carbon allocation, and hydraulics respectively- are selected for precise combinations, and further determine leaf size variation possibilities

Summary

Introduction

1. the leaf economic spectrum has deepened our understanding of leaf trait variability, little is known about how leaf traits scale with leaf area. The leaf economic spectrum has deepened our understanding of leaf trait variability, little is known about how leaf traits scale with leaf area This uncertainty has resulted in the assumption that leaf traits should vary by keeping the same pace of variation with increases in leaf area across the leaf size range. Cecropia is a Neotropical genus of pioneer trees that can exhibit large laminas (0.4 m2 for C. obtusa), with leaf size ranging by two orders of magnitude. We found that increasing xylem hydraulic efficiency with vessel size results in lower leaf lamina area: xylem ratios, which results in potential carbon savings for large leaves. We found that the vessel widening is consistent with hydraulic optimisation models

Objectives

Methods

Results

Discussion

Conclusion