Wood allocation trade-offs between fiber wall, fiber lumen, and axial parenchyma drive drought resistance in neotropical trees.

Thomas A J Janssen,Han Dolman,Katrin Fleischer,Teemu Hölttä,Kim Naudts

doi:10.1111/pce.13687

Thomas A J Janssen, Han Dolman + Show 3 more

Open Access

https://doi.org/10.1111/pce.13687

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Abstract

Functional relationships between wood density and measures of xylem hydraulic safety and efficiency are ambiguous, especially in wet tropical forests. In this meta‐analysis, we move beyond wood density per se and identify relationships between xylem allocated to fibers, parenchyma, and vessels and measures of hydraulic safety and efficiency. We analyzed published data of xylem traits, hydraulic properties and measures of drought resistance from neotropical tree species retrieved from 346 sources. We found that xylem volume allocation to fiber walls increases embolism resistance, but at the expense of specific conductivity and sapwood capacitance. Xylem volume investment in fiber lumen increases capacitance, while investment in axial parenchyma is associated with higher specific conductivity. Dominant tree taxa from wet forests prioritize xylem allocation to axial parenchyma at the expense of fiber walls, resulting in a low embolism resistance for a given wood density and a high vulnerability to drought‐induced mortality. We conclude that strong trade‐offs between xylem allocation to fiber walls, fiber lumen, and axial parenchyma drive drought resistance in neotropical trees. Moreover, the benefits of xylem allocation to axial parenchyma in wet tropical trees might not outweigh the consequential low embolism resistance under more frequent and severe droughts in a changing climate.

Highlights

Neotropical forests store large amounts of carbon in living biomass and are among the most species-rich ecosystems on Earth (Gloor et al, 2012; Hoorn et al, 2010)
There was no significant relationship between P50 and ray parenchyma fraction or vessel lumen fraction. These results suggest that compared to embolism vulnerable taxa, embolism resistant taxa are associated with higher fiber and vessel wall fractions and lower fiber lumen and axial parenchyma fractions
We find that low wood density tree species invest a relatively large proportion of their xylem volume to fiber lumen, which is the reason for their low wood density (Figure 2c,d)

Summary

| INTRODUCTION

Christensen-Dalsgaard, Ennos, & Fournier, 2007; Hoeber et al, 2014; Markesteijn, Poorter, Bongers, et al, 2011; Méndez-Alonzo et al, 2012) the importance of fibers and parenchyma in this respect has received less attention (Fortunel, Ruelle, Beauchêne, Fine, & Baraloto, 2014; Osazuwa-Peters, Wright, & Zanne, 2017; Poorter et al, 2010) This study fills this gap, motivated by the evidence from Mediterranean climate shrub ecosystems that trade-offs in xylem volume allocation are driving interspecific variability in embolism resistance and sapwood capacitance (Jacobsen et al, 2005; Jacobsen, Esler, Brandon Pratt, & Ewers, 2009; Pratt et al, 2007). We aim to move beyond wood density as a driver of hydraulic properties and as such improve our understanding of xylem volume allocation in determining drought resistance

| MATERIALS AND METHODS

| RESULTS

Findings

| DISCUSSION