The Leaf Economics Spectrum Constrains Phenotypic Plasticity Across a Light Gradient.

Xiaoping Chen,Karl J Niklas,Sean T Michaletz,Jun Sun,Quanlin Zhong,Dongliang Cheng,Mantang Wang,Min Lyu

doi:10.3389/fpls.2020.00735

Abstract

The leaf economics spectrum (LES) characterizes multivariate correlations that confine the global diversity of leaf functional traits onto a single axis of variation. Although LES is well established for traits of sun leaves, it is unclear how well LES characterizes the diversity of traits for shade leaves. Here, we evaluate LES using the sun and shade leaves of 75 woody species sampled at the extremes of a within-canopy light gradient in a subtropical forest. Shading significantly decreased the mean values of LMA and the rates of photosynthesis and dark respiration, but had no discernable effect on nitrogen and phosphorus content. Sun and shade leaves manifested the same relationships among Nmass, Pmass, Amass, and Rmass (i.e., the slopes of log–log scaling relations of LES traits did not differ between sun and shade leaves). However, the difference between the normalization constants of shade and sun leaves was correlated with functional trait plasticity. Although the generality of this finding should be evaluated further using larger datasets comprising more phylogenetically diverse taxa and biomes, these findings support a unified LES across shade as well as sun leaves.

Highlights

IntroductionA central premise of trait-based ecology is that performance and functioning across levels of organization, from organs to ecosystems, are predictable from organ-level functional traits (Niklas, 1994; Westoby et al, 2002; Hallik et al, 2009; Adler et al, 2014; Wullschleger et al, 2014; Fisher et al, 2015; Christoffersen et al, 2016; Díaz et al, 2016; McDowell et al, 2018)
The data used to construct the leaf economics spectrum (LES) is primarily based on the functional traits of sun leaves and it is unclear whether the trends established by the LES extend to shade leaves
The mean value of leaf mass per area (LMA) decreased from 83.68 g m−2 in sun leaves to 75.25 g m−2 in shade

Summary

Introduction

A central premise of trait-based ecology is that performance and functioning across levels of organization, from organs to ecosystems, are predictable from organ-level functional traits (Niklas, 1994; Westoby et al, 2002; Hallik et al, 2009; Adler et al, 2014; Wullschleger et al, 2014; Fisher et al, 2015; Christoffersen et al, 2016; Díaz et al, 2016; McDowell et al, 2018). The LES is shaped by the joint effects of environmental filtering and biophysical constraints on leaf carbon economics, yielding emergent functional tradeoffs between assimilation rate, leaf longevity, and leaf construction costs (Chabot and Hicks, 1982; Westoby et al, 2002; Kikuzawa and Lechowicz, 2006; Michaletz et al, 2015, 2016; Anderegg et al, 2018) These trade-offs have been demonstrated primarily using global-scale data, and thereby provide a general mechanistic framework for understanding and predicting variations of plant community structure and function across resource availability gradients. At the other end of the spectrum, leaves exposed to high light conditions are predicted to have lower LMA and higher Nmass, Pmass, Rmass, and Amass, but shorter lifespans (Chabot and Hicks, 1982; Mooney and Gulmon, 1982; Merino et al, 1984; Wright et al, 2004; Kikuzawa et al, 2013; Reich, 2014)

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