Large sensitivity in land carbon storage due to geographical and temporal variation in the thermal response of photosynthetic capacity.

Lina M Mercado,Przemyslaw Zelazowski,Rebecca J Oliver,Anna B Harper,Chris Huntingford,Douglas B Clark,Stephen Sitch,Peter M Cox,Belinda E Medlyn,Jens Kattge

doi:10.1111/nph.15100

Abstract

Summary Plant temperature responses vary geographically, reflecting thermally contrasting habitats and long‐term species adaptations to their climate of origin. Plants also can acclimate to fast temporal changes in temperature regime to mitigate stress. Although plant photosynthetic responses are known to acclimate to temperature, many global models used to predict future vegetation and climate–carbon interactions do not include this process.We quantify the global and regional impacts of biogeographical variability and thermal acclimation of temperature response of photosynthetic capacity on the terrestrial carbon (C) cycle between 1860 and 2100 within a coupled climate–carbon cycle model, that emulates 22 global climate models.Results indicate that inclusion of biogeographical variation in photosynthetic temperature response is most important for present‐day and future C uptake, with increasing importance of thermal acclimation under future warming. Accounting for both effects narrows the range of predictions of the simulated global land C storage in 2100 across climate projections (29% and 43% globally and in the tropics, respectively).Contrary to earlier studies, our results suggest that thermal acclimation of photosynthetic capacity makes tropical and temperate C less vulnerable to warming, but reduces the warming‐induced C uptake in the boreal region under elevated CO2.

Highlights

The response of plant productivity to climate change is a key uncertainty in Earth system models (ESMs; Friedlingstein et al, 2006)
Common-garden experiments demonstrate that there is a genetic component to the temperature response of photosynthesis, with species or provenances originating from cool environments commonly showing lower optimal temperatures than those originating from warmer environments (Ferrar et al, 1989; Cunningham & Read, 2003; Reich et al, 2015; Varhammar et al, 2015)
In order to understand projected regional and global predictions, we examined the individual geographical and thermal acclimation effects on the temperature response of light-saturated gross photosynthetic uptake for sunlit leaves at the leaf level in three randomly selected gridcells for three plant functional types (PFTs) based on a land cover map (Poulter et al, 2015), within boreal & tundra, temperate and tropical environments

Summary

Introduction

The response of plant productivity to climate change is a key uncertainty in Earth system models (ESMs; Friedlingstein et al, 2006). Because the response of photosynthesis to warming depends on whether the prevailing leaf temperature is above or below the optimum, the modelled feedback to climate from land surface carbon (C) uptake is highly sensitive to the value assumed for this optimum temperature (Booth et al, 2012). Plants growing at low temperatures typically attain their maximum photosynthetic capacity at lower temperatures than do plants growing at warmer temperatures (Berry & Bjorkman, 1980). This variation reflects short-term acclimation processes as well as longerterm processes such as genetic adaptation of species to a particular location and/or geographical variation in species composition (Yamori et al, 2013; Vanderwel et al, 2015). Over short timescales (days, months, up to seasons), plants can adjust

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