Thermal tolerance of Acer campestre (field maple) under heat and drought stress derived from chlorophyll fluorescence

Thermal tolerance of Acer campestre (field maple) under heat and drought stress derived from chlorophyll fluorescence | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Thermal tolerance of Acer campestre (field maple) under heat and drought stress derived from chlorophyll fluorescence Ramla Khan, Philip Wheeler, David Gowing This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6977009/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Climate change is intensifying extreme heat events, making the thermal tolerance of street trees increasingly crucial for sustainable urban forestry. In this study, we quantified the physiological responses of Acer campestre (field maple) to heat stress under varying hydration conditions by measuring chlorophyll fluorescence parameters. We assessed critical temperature thresholds (T crit ) and temperature at 50% reduction in photosystem II efficiency (T 50 ) through four experimental trials, with the final trial incorporating drought stress. Our results demonstrated significant hydration-dependent plasticity in thermal tolerance thresholds. Well-watered specimens exhibited T crit values of 37.0–44.0°C, which declined sharply to 29.0°C under drought conditions. Following 24-hour rehydration, T crit significantly increased across all trials (t = 7.63, df = 31, p < 0.01), with the most pronounced recovery in drought-stressed specimens from 29.0°C to 42.0°C with a mean difference of 8.81°C (95% CI: 6.46–11.17°C). In contrast, T 50 values remained relatively stable (47.0–50.0°C) with only modest post-hydration of mean difference 1.19°C (t = 2.83, df = 31, p < 0.01, 95% CI: 0.33–2.04°C). Principal component analysis revealed that hydration status explained 80.41% of variation in thermal responses, with K-means clustering (silhouette score = 0.45) separating samples into distinct hydrated and non-hydrated physiological groups. PERMANOVA confirmed significant treatment effects on multivariate thermal profiles (F = 5.47, R² = 0.41, p = 0.001). The significant correlation between T crit and T 50 (r = 0.61, p < 0.01, 95% CI: 0.43–0.74°C) suggested coordinated protection across different levels of thermal stress. These findings demonstrate that immediate hydration status, rather than prior drought conditioning, predominantly determines thermal resilience in Acer campestre , with critical implications for urban tree management under increasingly frequent heat extremes. Full Text Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6977009","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":491736830,"identity":"5c5ddb40-cf0d-4d12-badf-98fa8fa13a09","order_by":0,"name":"Ramla Khan","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABEklEQVRIie2RMUsDMRTH/+XgpuitKRb9CumiW7+IS0LgpotLlxscDoR2KX4Bi/0K6aJrysEtprjeIFKXTldwKg5FGo4OCteqm0N+8Ibw3o/8Hw/weP4nLQNwDgQG5FuDNI7X7JSQ/1kh7HfKxfCJmw/EV9HdaL2o0tfLsywoKK57YNY0Kh2r9GyEpE9f5o/dse0rbULJUEiwedaoULgZglRkpXo4ORpwpUG6C4QG7Lk5GI1WerZxyqRMlrUyyQgz+DygUKVzgkToMglrJTPul9bA7A9GVzrvsFhMy/i8PbYuWO52EbeStPesTyM1fatSKe5LuaRV6oINbwr6vu6dHlvenKyGfX0ErvjBQ3o8Ho/nJ7am72KIjyxRPwAAAABJRU5ErkJggg==","orcid":"","institution":"The Open University","correspondingAuthor":true,"prefix":"","firstName":"Ramla","middleName":"","lastName":"Khan","suffix":""},{"id":491736831,"identity":"6e8e6c4f-fba2-4eaa-aa85-121f4553a513","order_by":1,"name":"Philip Wheeler","email":"","orcid":"","institution":"The Open University","correspondingAuthor":false,"prefix":"","firstName":"Philip","middleName":"","lastName":"Wheeler","suffix":""},{"id":491736834,"identity":"8f1b498e-9468-41de-baee-138e2d3b031e","order_by":2,"name":"David Gowing","email":"","orcid":"","institution":"The Open University","correspondingAuthor":false,"prefix":"","firstName":"David","middleName":"","lastName":"Gowing","suffix":""}],"badges":[],"createdAt":"2025-06-25 17:23:25","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6977009/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6977009/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":88601810,"identity":"72484d06-46fd-4acc-81ed-c7ad1870e734","added_by":"auto","created_at":"2025-08-08 08:02:25","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":868659,"visible":true,"origin":"","legend":"","description":"","filename":"ManuscriptR3.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6977009/v1_covered_08c928dc-0ff6-477b-8c32-6048ab301f1c.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Thermal tolerance of Acer campestre (field maple) under heat and drought stress derived from chlorophyll fluorescence","fulltext":[],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":false,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":true,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":true,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-6977009/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6977009/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eClimate change is intensifying extreme heat events, making the thermal tolerance of street trees increasingly crucial for sustainable urban forestry. In this study, we quantified the physiological responses of \u003cem\u003eAcer campestre\u003c/em\u003e (field maple) to heat stress under varying hydration conditions by measuring chlorophyll fluorescence parameters. We assessed critical temperature thresholds (T\u003csub\u003ecrit\u003c/sub\u003e) and temperature at 50% reduction in photosystem II efficiency (T\u003csub\u003e50\u003c/sub\u003e) through four experimental trials, with the final trial incorporating drought stress. Our results demonstrated significant hydration-dependent plasticity in thermal tolerance thresholds. Well-watered specimens exhibited T\u003csub\u003ecrit\u003c/sub\u003e values of 37.0\u0026ndash;44.0\u0026deg;C, which declined sharply to 29.0\u0026deg;C under drought conditions. Following 24-hour rehydration, T\u003csub\u003ecrit\u003c/sub\u003e significantly increased across all trials (t\u0026thinsp;=\u0026thinsp;7.63, df\u0026thinsp;=\u0026thinsp;31, p\u0026thinsp;\u0026lt;\u0026thinsp;0.01), with the most pronounced recovery in drought-stressed specimens from 29.0\u0026deg;C to 42.0\u0026deg;C with a mean difference of 8.81\u0026deg;C (95% CI: 6.46\u0026ndash;11.17\u0026deg;C). In contrast, T\u003csub\u003e50\u003c/sub\u003e values remained relatively stable (47.0\u0026ndash;50.0\u0026deg;C) with only modest post-hydration of mean difference 1.19\u0026deg;C (t\u0026thinsp;=\u0026thinsp;2.83, df\u0026thinsp;=\u0026thinsp;31, p\u0026thinsp;\u0026lt;\u0026thinsp;0.01, 95% CI: 0.33\u0026ndash;2.04\u0026deg;C). Principal component analysis revealed that hydration status explained 80.41% of variation in thermal responses, with K-means clustering (silhouette score\u0026thinsp;=\u0026thinsp;0.45) separating samples into distinct hydrated and non-hydrated physiological groups. PERMANOVA confirmed significant treatment effects on multivariate thermal profiles (F\u0026thinsp;=\u0026thinsp;5.47, R\u0026sup2; = 0.41, p\u0026thinsp;=\u0026thinsp;0.001). The significant correlation between T\u003csub\u003ecrit\u003c/sub\u003e and T\u003csub\u003e50\u003c/sub\u003e (r\u0026thinsp;=\u0026thinsp;0.61, p\u0026thinsp;\u0026lt;\u0026thinsp;0.01, 95% CI: 0.43\u0026ndash;0.74\u0026deg;C) suggested coordinated protection across different levels of thermal stress. These findings demonstrate that immediate hydration status, rather than prior drought conditioning, predominantly determines thermal resilience in \u003cem\u003eAcer campestre\u003c/em\u003e, with critical implications for urban tree management under increasingly frequent heat extremes.\u003c/p\u003e","manuscriptTitle":"Thermal tolerance of Acer campestre (field maple) under heat and drought stress derived from chlorophyll fluorescence","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-07-29 14:13:14","doi":"10.21203/rs.3.rs-6977009/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"414a2b88-7e93-4ab0-85c8-4c82d294392a","owner":[],"postedDate":"July 29th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-02-27T14:56:25+00:00","versionOfRecord":[],"versionCreatedAt":"2025-07-29 14:13:14","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6977009","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6977009","identity":"rs-6977009","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}