Editing IPCC:AR6/WGI/Chapter-5 (section)

==== 5.4.3.1 Plant Physiology ====

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Plant productivity is highly dependent on local climate. In cold environments, warming has generally led to an earlier onset of the growing season, and with it an increase in early season vegetation productivity (e.g., [[#Forkel--2016|Forkel et al., 2016]] ). However, this trend is affected by the adverse effects of climate variability, and other emerging limitations on vegetation production by water, energy and nutrients, which may gradually reduce the effects of warming ( [[#Piao--2017|Piao et al., 2017]] ; [[#Buermann--2018|Buermann et al., 2018]] ; [[#Liu--2019|Liu et al., 2019]] ). At centennial time scales, boreal forest expansion may act as a climate-driven carbon sink ( [[#Pugh--2018|Pugh et al., 2018]] ).

In tropical and temperate environments, temperature simultaneously affects the metabolic rates of photosynthetic processes within leaf tissues, as well as the vapour pressure deficit that drives transpiration, its control by leaf stomata, and the resulting soil and plant tissue water content. Thus the direct effect of warming on photosynthesis can be positive, negative, or invariant depending on the environmental context ( [[#Lin--2012|Lin et al., 2012]] ; [[#Yamori--2014|Yamori et al., 2014]] ; [[#Smith--2017|Smith and Dukes, 2017]] ; [[#Grossiord--2020|Grossiord et al., 2020]] ). Observations and models suggest that the vapour pressure deficit effects are stronger than direct temperature effects on enzyme activities ( [[#Smith--2020|Smith et al., 2020]] ), and that acclimation of photosynthetic optimal temperature may mitigate productivity losses of tropical forests under climate change ( [[#Kattge--2007|Kattge and Knorr, 2007]] ; [[#Tan--2017|Tan et al., 2017]] ; [[#Kumarathunge--2019|Kumarathunge et al., 2019]] ). Some models have begun to include these acclimation responses in photosynthesis and autotrophic respiration ( [[#Lombardozzi--2015|Lombardozzi et al., 2015]] ; [[#Smith--2015|Smith et al., 2015]] ; [[#Huntingford--2017|Huntingford et al., 2017]] ; [[#Mercado--2018|Mercado et al., 2018]] ).

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