Photosynthetic temperature responses of tree species in Rwanda: evidence of pronounced negative effects of high temperature in montane rainforest climax species.

Angelica Vårhammar,Christopher M Mclean,Mirindi Eric Dusenge,Johan Uddling,Belinda E Medlyn,Donat Nsabimana,Göran Wallin,Thomas B Hasper

doi:10.1111/nph.13291

Abstract

The sensitivity of photosynthetic metabolism to temperature has been identified as a key uncertainty for projecting the magnitude of the terrestrial feedback on future climate change. While temperature responses of photosynthetic capacities have been comparatively well investigated in temperate species, the responses of tropical tree species remain unexplored. We compared the responses of seedlings of native cold-adapted tropical montane rainforest tree species with those of exotic warm-adapted plantation species, all growing in an intermediate temperature common garden in Rwanda. Leaf gas exchange responses to carbon dioxide (CO2 ) at different temperatures (20-40°C) were used to assess the temperature responses of biochemical photosynthetic capacities. Analyses revealed a lower optimum temperature for photosynthetic electron transport rates than for Rubisco carboxylation rates, along with lower electron transport optima in the native cold-adapted than in the exotic warm-adapted species. The photosynthetic optimum temperatures were generally exceeded by daytime peak leaf temperatures, in particular in the native montane rainforest climax species. This study thus provides evidence of pronounced negative effects of high temperature in tropical trees and indicates high susceptibility of montane rainforest climax species to future global warming.

Highlights

Observations have unequivocally demonstrated increasing global surface air temperatures (Hartmann et al, 2013), and global climate change models project a continuation of temperature increase over the coming century, irrespective of the chosen emission scenario (IPCC, 2013; Burrows et al, 2014)
The sensitivity of photosynthetic metabolism to temperature has been identified as a key uncertainty for projecting the magnitude of the terrestrial feedback on future climate change
We compared the responses of seedlings of native cold-adapted tropical montane rainforest tree species with those of exotic warm-adapted plantation species, all growing in an intermediate temperature common garden in Rwanda

Summary

Introduction

Observations have unequivocally demonstrated increasing global surface air temperatures (Hartmann et al, 2013), and global climate change models project a continuation of temperature increase over the coming century, irrespective of the chosen emission scenario (IPCC, 2013; Burrows et al, 2014). Improving the understanding of the effect of temperature on terrestrial plant species is important, as most migrate far more slowly than would be necessary to remain in a suitable climate under mid- and high-range rates of global warming (IPCC, 2013, 2014). It is paramount to understand the responses of plant primary production to climate change in order to project terrestrial feedbacks on the carbon cycle along with the potential of the terrestrial biosphere to be either mitigative or promotive to further global warming (Cox et al, 2000; Cao et al, 2001; Bonan, 2008). The sensitivity of photosynthetic metabolism to temperature has been identified as the most important uncertainty with respect to projections of the magnitude of the terrestrial feedback on future climate change, highlighting the need for a better understanding of plant photosynthetic responses to high temperature (Booth et al, 2012)

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