Species-independent down-regulation of leaf photosynthesis and respiration in response to shading: evidence from six temperate tree species.

Anping Chen,Stephen W Pacala,Jeremy W Lichstein,Jeanne L D Osnas,Keping Ma

doi:10.1371/journal.pone.0091798

Abstract

The ability to down-regulate leaf maximum net photosynthetic capacity (Amax) and dark respiration rate (Rdark) in response to shading is thought to be an important adaptation of trees to the wide range of light environments that they are exposed to across space and time. A simple, general rule that accurately described this down-regulation would improve carbon cycle models and enhance our understanding of how forest successional diversity is maintained. In this paper, we investigated the light response of Amax and Rdark for saplings of six temperate forest tree species in New Jersey, USA, and formulated a simple model of down-regulation that could be incorporated into carbon cycle models. We found that full-sun values of Amax and Rdark differed significantly among species, but the rate of down-regulation (proportional decrease in Amax or Rdark relative to the full-sun value) in response to shade was not significantly species- or taxon-specific. Shade leaves of sun-grown plants appear to follow the same pattern of down-regulation in response to shade as leaves of shade-grown plants. Given the light level above a leaf and one species-specific number (either the full-sun Amax or full-sun Rdark), we provide a formula that can accurately predict the leaf's Amax and Rdark. We further show that most of the down regulation of per unit area Rdark and Amax is caused by reductions in leaf mass per unit area (LMA): as light decreases, leaves get thinner, while per unit mass Amax and Rdark remain approximately constant.

Highlights

Plant photosynthesis and respiration are critical components of carbon cycle models from individual to global scales [1,2,3,4]
We focus on differences between sun- and shade-grown leaves, rather than acclimation by individual leaves exposed to different light levels
Because Rdark was measured after less than a full night-length of darkness, the Rdark values we report may not be directly comparable to some values reported in the literature

Summary

Introduction

Plant photosynthesis and respiration are critical components of carbon cycle models from individual to global scales [1,2,3,4]. An important challenge for modelers is that Amax and Rdark vary widely within and between individuals and species in response to environmental factors such as light level [6,7]. Light is a critical resource controlling the carbon budget of plant photosynthesis and respiration [8,9], and many studies have examined leaf Amax and Rdark in contrasting light environments (e.g., Sims and Pearcy [10]). Limited information on how sapling Amax and Rdark vary within and between individuals and species is problematic for next-generation global vegetation models that represent individual-level height-structured competition [3,15], because sapling understory performance exerts a strong impact on forest dynamics [16]

Methods

Results

Conclusion