Size-dependent changes in wood chemical traits: a comparison of neotropical saplings and large trees

Adam R Martin,Yong Zhao,Sean C Thomas

doi:10.1093/aobpla/plt039

Abstract

Wood anatomical traits are important correlates of life-history strategies among tree species, yet little is known about wood chemical traits. Additionally, size-dependent changes in wood chemical traits have been rarely examined,althoughthesechangesmayrepresent animportantaspectoftreeontogeny.Owingtoselectionforpatho- gen resistance and biomechanical stability, we predicted that saplings would show higher lignin (L) and wood carbon (Cconv), and lower holocellulose (H) concentrations, compared with conspecific large trees. To test these expectations, we quantified H, L and Cconv in co-occurring Panamanian tree species at the large tree vs. sapling size classes. We also examined inter- and intraspecific patterns using multivariate and phylogenetic analyses. In 15 of 16 species, sapling L concentration was higher than that in conspecific large trees, and in all 16 species, sapling H was lower than that in conspecific large trees. In 16 of 24 species, Cconv was higher in saplings than conspecific large trees. All large-tree traits were unrelated to sapling values and were unrelated to four life-history variables. Wood chemical traits did not show a phylogenetic signal in saplings, instead showing similar values across distantly related taxa; in large trees, only H showed a significant phylogenetic signal. Size-dependent changes in wood chemistry show consistent and pre- dictable patterns, suggesting that ontogenetic changes in wood chemical traits are an important aspect of tree func- tional biology. Our results are consistent with the hypothesis that at early ontogenetic stages, trees are selected for greater L to defend against cellulose-decaying pathogens, or possibly to confer biomechanical stability.

Highlights

In recent years, certain wood functional traits, namely wood density (WD), xylem vessel anatomy and wood carbon (C) concentration, have become of considerable interest to ecologists and plant biologists
Values for WD were taken from Wright et al (2010), which were based on tree cores taken previously from the exact trees we cored for H, L and carbon conversion factor (Cconv) analysis in this study
We observed a consistent trend whereby saplings showed lower H, lower H: L ratio, and greater L when compared with conspecific large trees (Table 1, Fig. 1) [see Supporting Information Figs 1 and 2]

Summary

Introduction

Certain wood functional traits, namely wood density (WD), xylem vessel anatomy and wood carbon (C) concentration, have become of considerable interest to ecologists and plant biologists. This interest has been promoted by numerous studies finding significant correlations between wood traits and tree demographic rates Martin et al — Size-dependent changes in wood chemical traits of trees understood when compared with other notable suites of functional traits such as leaf traits, reproductive traits or tree size metrics (reviewed by Westoby et al 2002). For tropical trees, this is largely because wood chemical traits have received very little attention, in contrast to anatomical traits. Large databases currently contain 6200 species-specific WD values for tropical trees (Zanne et al 2009), but ,150 species-specific records for wood C in tropical hardwoods (Thomas and Martin 2012)

Methods

Results

Discussion

Conclusion