{"id":1530,"date":"2026-01-30T16:59:56","date_gmt":"2026-01-30T16:59:56","guid":{"rendered":"https:\/\/research.reading.ac.uk\/palaeoclimate\/?p=1530"},"modified":"2026-01-30T17:01:02","modified_gmt":"2026-01-30T17:01:02","slug":"1530-2","status":"publish","type":"post","link":"https:\/\/research.reading.ac.uk\/palaeoclimate\/1530-2\/","title":{"rendered":"Optimality theory captures global sapwood:leaf area ratio in a new study"},"content":{"rendered":"<p>A new paper from SPECIAL group <strong>PI Sandy Harrison<\/strong> has recently been published in <a href=\"https:\/\/nph.onlinelibrary.wiley.com\/doi\/abs\/10.1111\/nph.70916\"><em>New Phytologist<\/em><\/a>. The paper looks at the ratio between sapwood to leaf area in plants using optimality theory. This addresses the important trade off between water acquisition and the costs of carbon construction. Plants face a fundamental coordination problem: how much carbon to invest in water transport tissues to support a given leaf area. Too little sapwood, and water supply limits photosynthesis; too much, and carbon is wasted on unnecessary hydraulic infrastructure.<\/p>\n<p data-start=\"240\" data-end=\"553\">This balance is captured by the Huber value (vH), the ratio of sapwood area to leaf area.<\/p>\n<p data-start=\"555\" data-end=\"844\">The new study by Huiying Xu and colleagues (including Prof. Harrison), shows that global patterns in vH can be explained by a simple organising principle: plants allocate sapwood and leaves to optimally balance water supply and water demand under local environmental conditions.<\/p>\n<h2 data-start=\"851\" data-end=\"878\">_____________________________________________________________________________________________________________________________________________________<\/h2>\n<p style=\"text-align: center\">You can read the full manuscript here: <a href=\"https:\/\/nph.onlinelibrary.wiley.com\/doi\/abs\/10.1111\/nph.70916\"><strong>Xu et al. 2026<\/strong><\/a><\/p>\n<p style=\"text-align: center\">Alternatively for a full summary see the <a href=\"https:\/\/research.reading.ac.uk\/lemontree\/sapwood-leaf-area-ratios\/\">blog post on the LEMONTREE project website<\/a>, or read on below for the highlights from that post.<\/p>\n<h2 data-start=\"851\" data-end=\"878\">_____________________________________________________________________________________________________________________________________________________<\/h2>\n<h2 style=\"letter-spacing: 0.08px\" data-start=\"1552\" data-end=\"1589\"><img loading=\"lazy\" decoding=\"async\" class=\"size-full wp-image-1531 aligncenter\" style=\"letter-spacing: 0.08px;font-size: 16px\" src=\"https:\/\/research.reading.ac.uk\/palaeoclimate\/wp-content\/uploads\/sites\/78\/2026\/01\/sapwood_ratio_paper_screenshot.png\" alt=\"\" width=\"1388\" height=\"442\" srcset=\"https:\/\/research.reading.ac.uk\/palaeoclimate\/wp-content\/uploads\/sites\/78\/2026\/01\/sapwood_ratio_paper_screenshot.png 1388w, https:\/\/research.reading.ac.uk\/palaeoclimate\/wp-content\/uploads\/sites\/78\/2026\/01\/sapwood_ratio_paper_screenshot-300x96.png 300w, https:\/\/research.reading.ac.uk\/palaeoclimate\/wp-content\/uploads\/sites\/78\/2026\/01\/sapwood_ratio_paper_screenshot-1024x326.png 1024w, https:\/\/research.reading.ac.uk\/palaeoclimate\/wp-content\/uploads\/sites\/78\/2026\/01\/sapwood_ratio_paper_screenshot-768x245.png 768w\" sizes=\"auto, (max-width: 1388px) 100vw, 1388px\" \/><\/h2>\n<h2 data-start=\"851\" data-end=\"878\">A simple optimality idea<\/h2>\n<p data-start=\"880\" data-end=\"921\">The study is built on one key assumption:<\/p>\n<ul data-start=\"923\" data-end=\"1060\">\n<li data-start=\"923\" data-end=\"1060\">\n<p data-start=\"925\" data-end=\"1060\">A plant\u2019s maximum water transport capacity should match its maximum water loss during photosynthesis.<\/p>\n<\/li>\n<\/ul>\n<p data-start=\"1062\" data-end=\"1179\">Using an eco-evolutionary optimality (EEO) framework, the authors derive an expression for optimal vH that links:<\/p>\n<ul>\n<li data-start=\"1183\" data-end=\"1234\"><strong data-start=\"1183\" data-end=\"1206\">Atmospheric dryness<\/strong> (vapour pressure deficit)<\/li>\n<li data-start=\"1237\" data-end=\"1261\"><strong data-start=\"1237\" data-end=\"1259\">Light availability<\/strong><\/li>\n<li data-start=\"1264\" data-end=\"1281\"><strong data-start=\"1264\" data-end=\"1279\">Temperature<\/strong><\/li>\n<li data-start=\"1284\" data-end=\"1355\"><strong data-start=\"1284\" data-end=\"1316\">Sapwood hydraulic efficiency<\/strong> (how easily water moves through xylem)<\/li>\n<\/ul>\n<p data-start=\"1357\" data-end=\"1545\">Photosynthetic traits are not fixed or tuned, but predicted using existing optimality models, allowing sapwood\u2013leaf area ratios to emerge naturally from climate and trait coordination.<\/p>\n<h2 data-start=\"1552\" data-end=\"1589\">Does the theory match real plants?<\/h2>\n<p data-start=\"1615\" data-end=\"1698\">When tested against large global datasets spanning species and climates, the model:<\/p>\n<ul>\n<li data-start=\"1702\" data-end=\"1775\">Explains nearly 60% of global variation in sapwood\u2013leaf area ratios<\/li>\n<li data-start=\"1778\" data-end=\"1835\">Reproduces observed patterns across major climate types<\/li>\n<li data-start=\"1838\" data-end=\"1899\">Requires only climate variables and a single fitted intercept<\/li>\n<\/ul>\n<h2 data-start=\"1982\" data-end=\"2028\">How climate shapes sapwood\u2013leaf area ratios<\/h2>\n<p data-start=\"2030\" data-end=\"2111\">The theory predicts clear and intuitive climate responses, all supported by data:<\/p>\n<ul>\n<li><strong>Higher vapour pressure deficit<\/strong> increases vH, reflecting greater investment in sapwood to sustain water supply under dry air conditions.<\/li>\n<li><strong>Higher irradiance<\/strong> also increases vH, as greater photosynthetic capacity raises transpirational demand.<\/li>\n<li><strong>Warmer temperatures<\/strong>, by contrast, tend to reduce vH, largely because warmer conditions enhance hydraulic efficiency and reduce the sapwood area needed to support a given leaf area.<\/li>\n<\/ul>\n<p data-start=\"2418\" data-end=\"2517\">Across all environments, sapwood-specific hydraulic conductivity is the dominant control on vH.<\/p>\n<h2 data-start=\"2524\" data-end=\"2543\"><\/h2>\n<h2 data-start=\"2524\" data-end=\"2543\">Why this matters<\/h2>\n<p data-start=\"2545\" data-end=\"2667\">Most vegetation models currently treat the Huber value as fixed, ignoring its sensitivity to climate. This study provides:<\/p>\n<ul>\n<li data-start=\"2671\" data-end=\"2744\">A mechanistic, theory-based alternative to fixed sapwood allocation<\/li>\n<li data-start=\"2747\" data-end=\"2809\">A clearer way to represent plant water use and carbon uptake<\/li>\n<li data-start=\"2812\" data-end=\"2875\">New insight into drought vulnerability under climate change<\/li>\n<\/ul>\n<h2 data-start=\"2882\" data-end=\"2906\"><\/h2>\n<h2 data-start=\"2882\" data-end=\"2906\">The take-home message<\/h2>\n<p data-start=\"2908\" data-end=\"3112\">Global diversity in plant hydraulic strategies is not arbitrary. It reflects a simple principle: plants balance leaves and water-transport tissues to maximise performance under climatic constraints.<\/p>\n<p>You can read the paper here:<\/p>\n<p>Xu, H., Wang, H., Prentice, I.C., <strong>Harrison, S.P<\/strong>., Rowland, L., Mencuccini, M., Sanchez- Martinez, P., He, P., Wright, I.J., Sitch, S., Li, M. &amp; Ye, Q. (2025). Global variation in the ratio of sapwood to leaf area explained by optimality principles. <em>New Phytologist, <\/em><a href=\"https:\/\/doi.org\/10.1111\/nph.70916\" target=\"_blank\" rel=\"noopener\"><strong>https:\/\/doi.org\/10.1111\/nph.70916<\/strong><\/a><\/p>\n<p>Blog post adapted, with permission, from the full blog post summary by Natalie Sanders &#8211;&gt; <a href=\"https:\/\/research.reading.ac.uk\/lemontree\/sapwood-leaf-area-ratios\/\">https:\/\/research.reading.ac.uk\/lemontree\/sapwood-leaf-area-ratios\/\u00a0\u00a0<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"<p>A new paper from SPECIAL group PI Sandy Harrison has recently been published in New Phytologist. The paper looks at the ratio between sapwood to leaf area in plants using&#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;&#49;&#53;&#51;&#48;&#45;&#50;&#47;\">Read More ><\/a><\/p>\n","protected":false},"author":959,"featured_media":1531,"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-1530","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 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>Optimality theory captures global sapwood:leaf area ratio in a new study - SPECIAL Palaeoclimate<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/research.reading.ac.uk\/palaeoclimate\/1530-2\/\" \/>\n<meta property=\"og:locale\" content=\"en_GB\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Optimality theory captures global sapwood:leaf area ratio in a new study - SPECIAL Palaeoclimate\" \/>\n<meta property=\"og:description\" content=\"A new paper from SPECIAL group PI Sandy Harrison has recently been published in New Phytologist. 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