{"id":1585,"date":"2026-04-15T13:00:21","date_gmt":"2026-04-15T12:00:21","guid":{"rendered":"https:\/\/research.reading.ac.uk\/palaeoclimate\/?p=1585"},"modified":"2026-04-15T13:00:21","modified_gmt":"2026-04-15T12:00:21","slug":"a-new-explanation-for-how-photosynthesis-acclimates-to-warming","status":"publish","type":"post","link":"https:\/\/research.reading.ac.uk\/palaeoclimate\/a-new-explanation-for-how-photosynthesis-acclimates-to-warming\/","title":{"rendered":"A new explanation for how photosynthesis acclimates to warming"},"content":{"rendered":"<p>S.P.E.C.I.A.L. group PhD Student <a href=\"https:\/\/research.reading.ac.uk\/palaeoclimate\/wenyao-gan\/\">Wenyao Gan<\/a> has recently published the first paper from her thesis in <em>New Phytologist<\/em>.\u00a0 The paper focuses on how photosynthesis acclimates to warming, in particular, how this process emerges from a Land Surface Model (LSM), JULES. A huge congratulations to Wenyao for achieving this milestone.<\/p>\n<p>_______________________________________________________________________________________________________________________________________________________________________________________________________________________________<\/p>\n<p style=\"text-align: center\"><a href=\"https:\/\/nph.onlinelibrary.wiley.com\/doi\/10.1111\/nph.71062\"> \u201cThis paper was actually an unexpected outcome. Our original plan was simply to incorporate the P-model into JULES, but during comparisons with the original JULES photosynthesis scheme we noticed an interesting pattern in thermal acclimation. Following that led to this study\u201d <span style=\"letter-spacing: 0.08px\">Wenyao Gan- PhD Student at the University of Reading (Supervised by Prof Sandy Harrison, Prof Pier Luigi Vidale, Prof Colin Prentice and Dr. Martin Best)<\/span><\/a><\/p>\n<p>_______________________________________________________________________________________________________________________________________________________________________________________________________________________________<\/p>\n<p>For decades, vegetation models have described photosynthesis using temperature response curves derived from the Farquhar model. These curves typically assume that parameters such as V<sub>cmax <\/sub>and J<sub>max<\/sub> respond to temperature in fixed, prescribed ways.<\/p>\n<p>But we know observations tell a different story.<\/p>\n<p>Across species and ecosystems:<\/p>\n<ul>\n<li>The thermal optimum of photosynthesis (T<sub>opt<\/sub>) increases when plants grow in warmer conditions.<\/li>\n<li>The maximum assimilation rate at that optimum (A<sub>opt<\/sub>) often declines at high growth temperatures.<\/li>\n<li>The ratio of J<sub>max25<\/sub> to V<sub>cmax25<\/sub> decreases with warming.<\/li>\n<\/ul>\n<p>In other words, plants acclimate. But how plants adjust their photosynthesis to long-term changes in temperature isn\u2019t fully understood. Most large-scale models account for this issue using empirical adjustments, for example by allowing activation energies or entropy terms in Arrhenius equations to vary with growth temperature. These approaches improve the model output, but they require parameter fitting and often differ by plant functional type (PFT).<\/p>\n<p>But a core question remains: Why does T<sub>opt <\/sub>shift with growth temperature? What mechanism explains this acclimation?<\/p>\n<h2>An eco-evolutionary optimality approach<\/h2>\n<p>Wenyao\u2019s study addresses this using the sub-daily P model, built on eco-evolutionary optimality (EEO) theory. Rather than prescribing how photosynthetic parameters should change, the model assumes that plants adjust traits to maximise carbon gain relative to costs under prevailing environmental conditions. These adjustments emerge dynamically from environmental drivers such as temperature, light, vapour pressure deficit (VPD) and CO\u2082.<\/p>\n<p>In this framework:<\/p>\n<ul>\n<li>The ratio of electron transport capacity (J<sub>max25<\/sub>) to carboxylation capacity (V<sub>cmax25<\/sub>) adjusts optimally.<\/li>\n<li>Stomatal behaviour adapts in coordination with photosynthetic capacity.<\/li>\n<li>No empirical temperature-dependent tuning parameters are required.<\/li>\n<\/ul>\n<p>What we wanted to know is whether this optimality framework can reproduce the observed thermal acclimation and the answer is yes!<\/p>\n<p>Model simulations show that under high light, T<sub>opt<\/sub> increases strongly with growth temperature from ~25\u00b0C when plants grow at 10\u00b0C to ~38\u00b0C when they grow at 40\u00b0C.<\/p>\n<p>Crucially, this shift is not imposed. It emerges from changing balance between the Rubisco-limited rates (A<sub>c <\/sub>and A<sub>j<\/sub>) and electron-transport limitation (J)<\/p>\n<p>At cooler growth temperatures, the temperature optimum of photosynthesis often lies in the electron transport\u2013limited regime. As growth temperature rises, the relative balance between these two limitations shifts. Because J<sub>max25<\/sub> declines relative to V<sub>cmax25<\/sub> under warming, the switch between A<sub>j<\/sub> and A<sub>c<\/sub> occurs at higher instantaneous temperatures. The result is a rightward shift in T<sub>opt.<\/sub><\/p>\n<p>This means T<sub>opt<\/sub> is not determined by a single biochemical parameter. It is an emergent property of coordinated adjustments between electron transport, carboxylation and stomatal conductance.<\/p>\n<p>The model also reproduces the observed decline in J<sub>max25<\/sub>\/V<sub>cmax25 <\/sub>with warming \u2014 a pattern long reported in experiments but poorly explained mechanistically.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"size-full wp-image-1586 aligncenter\" src=\"https:\/\/research.reading.ac.uk\/palaeoclimate\/wp-content\/uploads\/sites\/78\/2026\/04\/Picture2.jpg\" alt=\"\" width=\"704\" height=\"716\" srcset=\"https:\/\/research.reading.ac.uk\/palaeoclimate\/wp-content\/uploads\/sites\/78\/2026\/04\/Picture2.jpg 704w, https:\/\/research.reading.ac.uk\/palaeoclimate\/wp-content\/uploads\/sites\/78\/2026\/04\/Picture2-295x300.jpg 295w\" sizes=\"auto, (max-width: 704px) 100vw, 704px\" \/><\/p>\n<p style=\"text-align: center\"><em>Figure 1. Observed and modelled relationships between Jmax25\/Vcmax25 and growth temperature for woody species. Points represent values derived from observations (upper panel) and P model simulations driven by observed environmental conditions (lower panel).<\/em><\/p>\n<p><strong>\u00a0<\/strong><\/p>\n<h2>Observations across scales<\/h2>\n<p>The study compares simulations against two major data sources: Leaf-level gas exchange experiments (woody and non-woody species) and ecosystem-scale flux tower measurements (FLUXNET sites)<\/p>\n<h4>At the leaf level:<\/h4>\n<ul>\n<li>Observed T<sub>opt <\/sub>increases with growth temperature, especially in woody species.<\/li>\n<li>The model reproduces this positive relationship with strong agreement.<\/li>\n<li>The observed peaked relationship between normalised A<sub>opt <\/sub>and growth temperature is also captured.<\/li>\n<\/ul>\n<h4>At the ecosystem scale:<\/h4>\n<ul>\n<li>Across sites in Europe, North America and Australia, T<sub>opt<\/sub> derived from flux data increases by roughly 0.75\u20131.1\u00b0C per 1\u00b0C rise in growth temperature.<\/li>\n<li>The model predicts very similar sensitivities.<\/li>\n<li>The scatter around the relationship closely matches observations.<\/li>\n<\/ul>\n<p>Importantly, sensitivity tests show that using air temperature instead of leaf temperature at flux sites has negligible influence on the estimated T<sub>opt<\/sub> for the predominantly well-watered, temperate sites analysed.<\/p>\n<p>Together, these results demonstrate that acclimation is visible not just at the leaf scale under controlled conditions, but also at whole-ecosystem scale in real-world data. Using the sub-daily P model, it produces acclimation as a natural outcome of optimal coordination between photosynthetic processes and stomatal behaviour. No extra temperature-dependent tuning is required.<\/p>\n<p>This is particularly important for next-generation land-surface models such as JULES, where Wenyao\u2019s broader PhD work focuses on implementing eco-evolutionary optimality formulations for photosynthesis and primary production, dark respiration and stomatal behaviour.<\/p>\n<p>Blog post written by Natalie Sanders.<\/p>\n<h2>You can read the paper here:<\/h2>\n<p>Gan, W., Alizadeh, N., Best, M., Vidale, P.L., Prentice, I.C. and Harrison, S.P. (2026), An eco-evolutionary optimality model explains the acclimated temperature response of photosynthesis. New Phytol.\u00a0<a href=\"https:\/\/doi.org\/10.1111\/nph.71062\" aria-label=\"Digital Object Identifier\">https:\/\/doi.org\/10.1111\/nph.71062<\/a><\/p>\n<p>&nbsp;<\/p>\n","protected":false},"excerpt":{"rendered":"<p>S.P.E.C.I.A.L. group PhD Student Wenyao Gan has recently published the first paper from her thesis in New Phytologist.\u00a0 The paper focuses on how photosynthesis acclimates to warming, in particular, how&#8230;<a class=\"read-more\" href=\"&#104;&#116;&#116;&#112;&#115;&#58;&#47;&#47;&#114;&#101;&#115;&#101;&#97;&#114;&#99;&#104;&#46;&#114;&#101;&#97;&#100;&#105;&#110;&#103;&#46;&#97;&#99;&#46;&#117;&#107;&#47;&#112;&#97;&#108;&#97;&#101;&#111;&#99;&#108;&#105;&#109;&#97;&#116;&#101;&#47;&#97;&#45;&#110;&#101;&#119;&#45;&#101;&#120;&#112;&#108;&#97;&#110;&#97;&#116;&#105;&#111;&#110;&#45;&#102;&#111;&#114;&#45;&#104;&#111;&#119;&#45;&#112;&#104;&#111;&#116;&#111;&#115;&#121;&#110;&#116;&#104;&#101;&#115;&#105;&#115;&#45;&#97;&#99;&#99;&#108;&#105;&#109;&#97;&#116;&#101;&#115;&#45;&#116;&#111;&#45;&#119;&#97;&#114;&#109;&#105;&#110;&#103;&#47;\">Read More ><\/a><\/p>\n","protected":false},"author":959,"featured_media":1586,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"__cvm_playback_settings":[],"__cvm_video_id":"","footnotes":""},"categories":[22],"tags":[],"class_list":["post-1585","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-blog"],"acf":[],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v21.8.1 - 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