\n
![\"EarthSnap\"\/](\"https:\/\/www.europesays.com\/ie\/wp-content\/uploads\/2025\/08\/earthsnap-banner-news.webp.webp\")
\n<\/a><\/p>\n
As atmospheric CO2<\/a> has climbed, tree growth and long-term carbon storage have bounced around from \u201cup a bit\u201d to \u201cflat\u201d to \u201csometimes down.\u201d <\/p>\n This leaves scientists pondering how much of that patchwork is really about carbon in the air, and how much is everything else?<\/p>\n A new lens on a biological puzzle<\/p>\n A new study led by researchers from Duke University<\/a> and Wuhan University<\/a> argues that you can\u2019t answer those questions by looking at carbon alone. You have to account for water.\u00a0<\/p>\n The team built a model that treats a tree\u2019s daily decision \u2013 open leaf pores to grab carbon or close them to conserve water \u2013 as a dynamic optimization problem. <\/p>\n That framing, borrowed from engineering, turns out to reproduce decades of observations and explain why forests<\/a> don\u2019t simply ramp up growth in lockstep with CO2.<\/p>\n \u201cThere used to be a common assumption that higher levels of carbon dioxide will cause trees to grow more and store more carbon,\u201d said Gaby Katul, a professor of civil and environmental engineering at Duke.\u00a0<\/p>\n \u201cBut benchmark experiments showed that while this may be true in isolation, other environmental factors also play a large role. We have now uncovered some of the underlying mechanisms at work.\u201d<\/p>\n Lessons from two long experiments<\/p>\n Those \u201cbenchmarks\u201d come from rare, painstaking field experiments. At Duke, a forest plot spent 16 years bathed in extra CO2.<\/p>\n At ETH Zurich<\/a>, researchers dialed up local humidity. Both sites tracked growth, carbon uptake, leaf physiology, and a raft of environmental variables.\u00a0<\/p>\n The outcome was sobering. Trees did not sequester as much extra carbon as earlier, simple models predicted. The surprise wasn\u2019t the result but why this happened.<\/p>\n Rising CO2 and forest growth <\/p>\n To find the mechanism, Katul\u2019s team focused on the valves that govern a tree\u2019s economy: stomata, the tiny pores on leaves<\/a> that open to let in CO2 but simultaneously leak water vapor.\u00a0<\/p>\n In carbon-rich air, stomata don\u2019t need to open as wide to pull in the same amount of CO2, which should, in theory, boost water use efficiency and growth.\u00a0\u00a0<\/p>\n But warming and drying flip the calculus. Hotter, drier air ramps up evaporation through open pores. To protect their internal plumbing, trees constrict those pores, throttling water loss and, inevitably, carbon intake.<\/p>\n \u201cStomata are like valves that control how much water<\/a> is drawn up into the leaves and released into the air,\u201d Katul said. <\/p>\n That \u201cvalve\u201d manages a precarious tension that spans roots, trunk, and canopy. Lose too much water too fast and the transport columns inside xylem can snap like a straw, a risk that grows with tree height and heat stress.<\/p>\n Turning physiology into math<\/p>\n The team built a model that formalizes that trade-off: maximize carbon gain while keeping water loss within safe limits. They calibrated it with unusually rich data from the Duke and ETH Zurich sites.<\/p>\n At these sites, individual leaves were enclosed and exposed to tightly controlled shifts in temperature, humidity, and CO2 while researchers tracked stomatal behavior in real time.<\/p>\n When they ran the model forward, it did two things well. First, it reproduced the muted carbon gains seen at Duke under elevated CO2. <\/p>\n Second, it captured the humidity experiment\u2019s signal: when air is moist, stomata can stay open longer with less hydraulic risk, allowing higher carbon intake. In other words, CO2 matters, but so does the atmosphere\u2019s thirst.<\/p>\n Making sense of messy global records<\/p>\n Armed with that mechanistic backbone, the team turned to a patchwork of tropical forest studies spanning the past fifty years. <\/p>\n The records show head-scratching diversity: some plots greened faster, others barely changed, some even slowed.\u00a0Using the new framework, those contradictions look less mysterious. <\/p>\n In places where warmth and vapor pressure deficit climbed (air\u2019s \u201cdrying power\u201d), trees protected their plumbing by closing stomata more often \u2013 muting or canceling any CO2-driven growth bump.<\/p>\n Where moisture buffered the heat, gains were more likely to show up.<\/p>\n That reconciliation doesn\u2019t mean carbon enrichment never boosts growth. It means the size, and even the direction, of that boost depends on the local balance of carbon supply and water demand.<\/p>\n The effects are mediated through the microscopic leaf valves and the hydraulics behind them.<\/p>\n Beyond a single lever<\/p>\n No single model can capture the full sprawl of a forest\u2019s constraints. Nutrient<\/a> limits, soil water storage, species mix, pests, shifting seasons, and stand age all shape growth and carbon storage.\u00a0<\/p>\n The authors are clear that their framework is a foundation, not a finish line. It explains a big, stubborn piece of the puzzle \u2013 the coupling of CO2 gain to water loss \u2013 and does so at the leaf-to-tree scale where decisions are made.\u00a0<\/p>\n The next challenge is scaling those decisions up into regional and global climate models without smoothing away the very dynamics that matter.<\/p>\n \u201cThere is a lot of value in looking at these environmental and biological questions from an engineering perspective,\u201d Katul said. <\/p>\n \u201cFiguring out how best to ameliorate climate change<\/a> using nature-based green technology in the decades to come is going to take contributions from many disciplines.\u201d<\/p>\n Forest growth as CO2 rises <\/p>\n The takeaway isn\u2019t that forests won\u2019t help, or that CO2 fertilization is a myth. It\u2019s that nature\u2019s response is conditional.\u00a0<\/p>\n On hotter, drier days trees \u201cchoose\u201d survival over speed. They pull back on the very intake that would make them grow faster. <\/p>\n For policymakers and modelers, that argues for humility about banking on automatic forest gains from rising CO2.\u00a0<\/p>\n It also argues for sharpening strategies that protect the water side of the ledger, such as conserving soil moisture, limiting heat stress, and reducing other pressures that force trees into hydraulic triage.<\/p>\n In short: more carbon in the air does not guarantee more carbon in the wood. Between those two lies a living network of valves, vessels, and trade-offs, tuned by evolution to keep trees alive. If we want forests to store more for us, we have to keep them thirsty less.<\/p>\n \u2014\u2013<\/p>\n Like what you read? Subscribe to our newsletter<\/a> for engaging articles, exclusive content, and the latest updates.<\/p>\n Check us out on EarthSnap<\/a>, a free app brought to you by Eric Ralls<\/a> and Earth.com.<\/p>\n \u2014\u2013<\/p>\n","protected":false},"excerpt":{"rendered":"Plants absorb carbon dioxide and water, use sunlight to make sugars, and release oxygen. So if the air…\n","protected":false},"author":2,"featured_media":248968,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[77],"tags":[18,19,17,7262,133],"class_list":{"0":"post-248967","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-science","8":"tag-eire","9":"tag-ie","10":"tag-ireland","11":"tag-plants","12":"tag-science"},"share_on_mastodon":{"url":"https:\/\/pubeurope.com\/@ie\/115773620336667495","error":""},"_links":{"self":[{"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/posts\/248967","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/comments?post=248967"}],"version-history":[{"count":0,"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/posts\/248967\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/media\/248968"}],"wp:attachment":[{"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/media?parent=248967"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/categories?post=248967"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/tags?post=248967"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}