Consistent responses to moisture stress within diverse mountain fynbos communities revealed by multi-year in situ physiological measurements

Consistent responses to moisture stress within diverse mountain fynbos communities revealed by multi-year in situ physiological measurements | 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 Consistent responses to moisture stress within diverse mountain fynbos communities revealed by multi-year in situ physiological measurements Robert Paul Skelton, Adam Gerrard West, Daniel Buttner, Todd Dawson This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-1821506/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 24 Jan, 2023 Read the published version in Oecologia → Version 1 posted 4 You are reading this latest preprint version Abstract ● Understanding climate change impacts on the Cape Floristic Region requires improved knowledge of plant physiological responses to the environment. Prior studies examining physiological responses of fynbos species have consisted of campaign-based measurements, capturing snapshots in time of plant water relations and photosynthesis. We examine conclusions drawn from these studies by tracking in situ physiological responses of three species, representing three dominant growth forms (proteoid, ericoid, restioid), over two years using miniature continuous sap flow technology, in combination with long-term observations of xylem water potentials, gas exchange and assessments of xylem vulnerability to embolism. ● We observed considerable inter-specific variation in the timing and extent of dehydration-induced declines in productivity. Erica monsoniana (a shallow-rooted ericoid) exhibited steep within-season declines in sap flow and water potentials, and pronounced inter-annual variability in total daily sap flux (Js). Protea repens showed steady reductions in Js across both years, despite maintaining less negative water potentials. Cannomois congesta - a shallow-rooted restioid - was least negatively impacted. Following rehydrating rain at the end of summer we compared gas exchange recovery in the representative dry year with the normal year, finding significant seasonal, but not species, effects. Loss of function in the drier year was partially accounted for by loss of stem xylem transport capacity, but only in E. monsoniana and C. congesta. ● Hitherto unseen water-use patterns, including inter-annual variability of gas exchange that were driven by contrasting water uptake properties, reveal that mountain fynbos species use different mechanisms to cope with summer dry periods. drought ecophysiology plant water-use sap flow mountain fynbos Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Full Text Tables Table 1-3 are available in the Supplemental Files section. Plate Plate 1 is available in the Supplemental Files section. Supplementary Files Tables.pdf Plate01.jpg SupplementaryMaterial.pdf Cite Share Download PDF Status: Published Journal Publication published 24 Jan, 2023 Read the published version in Oecologia → Version 1 posted Reviewers agreed at journal 08 Jul, 2022 Reviewers invited by journal 06 Jul, 2022 Editor assigned by journal 05 Jul, 2022 First submitted to journal 03 Jul, 2022 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-1821506","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":119010698,"identity":"94e9f4ea-93dc-4d42-bfda-13f8e0d3c372","order_by":0,"name":"Robert Paul Skelton","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAxklEQVRIiWNgGAWjYDACHgbGAwwMB+RA7AMPiNTCANJiDNaSQIqWxAYQhygt8j2HDxyuqLiTPj/s8EOgLXZyug0EtBicbUs4eObMs9yNt9MMgFqSjc0OENLCz2NwsLHtcO7G2QkgLQcStxHSIt/P/wGkJd1wdvoH4rQwnO1hAGlJkJfOIdIWgzPHDA42nHlmuEE6p+BAggERfpHvSX74sKHijrz87PTNHz5U2MkR1IKwDqzSgFjlYOsaSFE9CkbBKBgFIwoAAAhfTyRSnGpoAAAAAElFTkSuQmCC","orcid":"https://orcid.org/0000-0003-2768-6420","institution":"SAEON: South African Environmental Observation Network","correspondingAuthor":true,"prefix":"","firstName":"Robert","middleName":"Paul","lastName":"Skelton","suffix":""},{"id":119010699,"identity":"e39643b8-2343-4de6-83cc-4c1d403439ae","order_by":1,"name":"Adam Gerrard West","email":"","orcid":"","institution":"University of Cape Town","correspondingAuthor":false,"prefix":"","firstName":"Adam","middleName":"Gerrard","lastName":"West","suffix":""},{"id":119010700,"identity":"5e60230e-81c0-41a1-8e70-0037da91cb24","order_by":2,"name":"Daniel Buttner","email":"","orcid":"","institution":"Nelson Mandela University Faculty of Science","correspondingAuthor":false,"prefix":"","firstName":"Daniel","middleName":"","lastName":"Buttner","suffix":""},{"id":119010701,"identity":"183deb27-f81a-494d-a9a3-5ff70b2d67e9","order_by":3,"name":"Todd Dawson","email":"","orcid":"","institution":"University of California Berkeley Department of Integrative Biology","correspondingAuthor":false,"prefix":"","firstName":"Todd","middleName":"","lastName":"Dawson","suffix":""}],"badges":[],"createdAt":"2022-07-03 20:48:50","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-1821506/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-1821506/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s00442-023-05326-9","type":"published","date":"2023-01-24T18:30:15+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":23858727,"identity":"a315443c-8f95-45e1-ba6b-418db488334e","added_by":"auto","created_at":"2022-07-14 14:29:12","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":618238,"visible":true,"origin":"","legend":"\u003cp\u003eTimeline of environmental variables and total daily sap flux density (Js) for each species recorded at the study site over the course of the study period. (a.) Mean daily midday vapour pressure deficit (VPD, kPa); (b.) soil moisture measured at a soil depth of 70cm (%); (c.) total daily rainfall (mm); and total daily sap flux density (Js, g cm-2 day-1) for Erica monsoniana (d), Cannomois congesta (e) and Protea repens (f). Six-month total rainfall amounts (for summer 2012/13, winter 2013, and summer 2013/14) are indicated in parentheses. Grey background shading indicates summer periods, blue shading indicates periods when soil moisture recovered following rehydrating rainfall events (see Methods for further details).\u003c/p\u003e","description":"","filename":"Figures1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-1821506/v1/44f5de740fae085e62098218.jpg"},{"id":23859095,"identity":"4b1c8507-d9d0-4fe5-a230-f0eb0ef5e6dd","added_by":"auto","created_at":"2022-07-14 14:34:12","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":496178,"visible":true,"origin":"","legend":"\u003cp\u003eRelationship between total daily sap flux density (Js) and soil moisture or midday vapour pressure deficit (VPD) for the three study species in the representative dry year (2012/13) and the normal year (2013/14). Relationships between variables were assessed using linear mixed effects models.\u0026nbsp;\u003c/p\u003e","description":"","filename":"Figures2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-1821506/v1/dff3b79568c277c3fed85cd3.jpg"},{"id":23858731,"identity":"91765062-60b8-44a2-921b-559dd68bd39f","added_by":"auto","created_at":"2022-07-14 14:29:12","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":380160,"visible":true,"origin":"","legend":"\u003cp\u003eTimeline of environmental variables and total daily sap flux density (Js) for each species recorded at the study site over mid-summer during the representative dry year (2013). (a.) Mean daily soil moisture measured at a soil depth of 70cm (%), total daily rainfall (mm), and duration of cloud/dew events; total daily sap flux density (Js, g cm-2 day-1) for Erica monsoniana (b), Cannomois congesta (c) and Protea repens (d).\u003c/p\u003e","description":"","filename":"Figures3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-1821506/v1/4b48a1ea6010e7333f1e115b.jpg"},{"id":23858735,"identity":"742508fe-2a50-49bc-9d69-7fd630e5e4e0","added_by":"auto","created_at":"2022-07-14 14:29:12","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":820838,"visible":true,"origin":"","legend":"\u003cp\u003eTimeline of mean midday sap flow derived stomatal conductance (Gsf; mean ± s.e.) expressed as a percentage of pre-stressed maximum Gsf for Erica monsoniana (a), Cannomois congesta (b), and Protea repens\u0026nbsp;(c). Grey shaded areas indicate periods in summer when plant xylem water potentials generally declined, blue shaded areas indicate periods when plant xylem water potentials recovered to pre-stressed values. Arrows indicate small summer rain events, vertical dashed lines indicate large rainfall events. For\u003c/p\u003e\u003cp\u003ecomparison, the leaf level stomatal conductance is also shown (red points; mean ± s.e.).\u0026nbsp;\u003c/p\u003e","description":"","filename":"Figures4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-1821506/v1/3394ea57798e7b3f9b4ed11f.jpg"},{"id":23859367,"identity":"c8d6341e-e99d-4773-bc07-358074f6052d","added_by":"auto","created_at":"2022-07-14 14:44:12","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":141908,"visible":true,"origin":"","legend":"\u003cp\u003eThe recovery of total daily Js (a) and Gsf (b) for each species in the representative dry year (2012/13) and the normal year (2013/14). Letters indicate statistical differences revealed by post-hoc tests.\u003c/p\u003e","description":"","filename":"Figures5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-1821506/v1/970dfdd640ccc9fdcb8204e7.jpg"},{"id":23859202,"identity":"1b6a0040-bdcf-4dd7-a4c9-3841a93e4845","added_by":"auto","created_at":"2022-07-14 14:39:12","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":370747,"visible":true,"origin":"","legend":"\u003cp\u003eTimeline of predawn and midday xylem water potential (mean ± s.e., n = 5) for the three study species over the course of the two summer study periods. Grey and blue shading is the same as for Figure 1.\u003c/p\u003e","description":"","filename":"Figures6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-1821506/v1/89fe65f9a83836c5cd11ecfe.jpg"},{"id":23858736,"identity":"53cf7c1d-c6e4-4da9-8102-ea6e277722be","added_by":"auto","created_at":"2022-07-14 14:29:12","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":328988,"visible":true,"origin":"","legend":"\u003cp\u003e(a-c) Stomatal conductance and water potential envelopes for three Jonaskop study species (orange and red points) and Silver mine species from West et al. 2012 (grey points). Also shown are the xylem vulnerability curves for the three sample species: solid black lines are mean xylem vulnerability curves for\u003c/p\u003e\u003cp\u003eeach species, grey lines are individual curves, and filled white circles indicate the P50 values for each species. Minimum xylem water potentials for each species are also shown. Bars indicate the range between minimum predawn and minimum midday water potentials recorded in 2012/13 and 2013/14. (d-f) The relationship between stomatal conductance and carbon assimilation measured for all three species in the representative dry year (2012/13) and the normal year (2013/14). Grey lines are best fit models of the relationships.\u003c/p\u003e","description":"","filename":"Figures7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-1821506/v1/0c01f83ae4a6c042ff2e0495.jpg"},{"id":23859499,"identity":"8895fe9f-5e8c-4ded-b9e1-e69da477a541","added_by":"auto","created_at":"2022-07-14 14:44:25","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":715042,"visible":true,"origin":"","legend":"","description":"","filename":"Manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-1821506/v1_covered.pdf"},{"id":23859092,"identity":"54a95799-9e89-414f-b216-182f8ad1d9a9","added_by":"auto","created_at":"2022-07-14 14:34:12","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":175567,"visible":true,"origin":"","legend":"","description":"","filename":"Tables.pdf","url":"https://assets-eu.researchsquare.com/files/rs-1821506/v1/1d95197758d257cbbf469305.pdf"},{"id":23858728,"identity":"5bf34897-6dcb-478d-9ec6-6e5608d4c1d5","added_by":"auto","created_at":"2022-07-14 14:29:12","extension":"jpg","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":2265769,"visible":true,"origin":"","legend":"","description":"","filename":"Plate01.jpg","url":"https://assets-eu.researchsquare.com/files/rs-1821506/v1/a0ee4eaff54959adb3d5f01a.jpg"},{"id":23859204,"identity":"76db2fe5-056b-4a59-a5e6-ad2fe7c5d4cf","added_by":"auto","created_at":"2022-07-14 14:39:12","extension":"pdf","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":432148,"visible":true,"origin":"","legend":"","description":"","filename":"SupplementaryMaterial.pdf","url":"https://assets-eu.researchsquare.com/files/rs-1821506/v1/3718a17a2ee2f1d9710b605d.pdf"}],"financialInterests":"","formattedTitle":"Consistent responses to moisture stress within diverse mountain fynbos communities revealed by multi-year in situ physiological measurements","fulltext":[{"header":"Full Text","content":"This preprint is available for \u003ca href='/article/rs-1821506/latest.pdf' target='_blank'\u003edownload as a PDF\u003c/a\u003e."},{"header":"Tables","content":"\u003cp\u003eTable 1-3 are available in the Supplemental Files section.\u003c/p\u003e"},{"header":"Plate","content":"\u003cp\u003ePlate 1 is available in the Supplemental Files section.\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":false,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":true,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":true,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"oecologia","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"oeco","sideBox":"Learn more about [Oecologia](https://www.springer.com/journal/442)","snPcode":"442","submissionUrl":"https://submission.nature.com/new-submission/442/3","title":"Oecologia","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"drought, ecophysiology, plant water-use, sap flow, mountain fynbos","lastPublishedDoi":"10.21203/rs.3.rs-1821506/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-1821506/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e● Understanding climate change impacts on the Cape Floristic Region requires improved knowledge of plant physiological responses to the environment. Prior studies examining physiological responses of fynbos species have consisted of campaign-based measurements, capturing snapshots in time of plant water relations and photosynthesis. We examine conclusions drawn from these studies by tracking in situ physiological responses of three species, representing three dominant growth forms (proteoid, ericoid, restioid), over two years using miniature continuous sap flow technology, in combination with long-term observations of xylem water potentials, gas exchange and assessments of xylem vulnerability to embolism. \u003c/p\u003e\u003cp\u003e● We observed considerable inter-specific variation in the timing and extent of dehydration-induced declines in productivity. Erica monsoniana (a shallow-rooted ericoid) exhibited steep within-season declines in sap flow and water potentials, and pronounced inter-annual variability in total daily sap flux (Js). Protea repens showed steady reductions in Js across both years, despite maintaining less negative water potentials. Cannomois congesta - a shallow-rooted restioid - was least negatively impacted. Following rehydrating rain at the end of summer we compared gas exchange recovery in the representative dry year with the normal year, finding significant seasonal, but not species, effects. Loss of function in the drier year was partially accounted for by loss of stem xylem transport capacity, but only in E. monsoniana and C. congesta. \u003c/p\u003e\u003cp\u003e● Hitherto unseen water-use patterns, including inter-annual variability of gas exchange that were driven by contrasting water uptake properties, reveal that mountain fynbos species use different mechanisms to cope with summer dry periods.\u003c/p\u003e","manuscriptTitle":"Consistent responses to moisture stress within diverse mountain fynbos communities revealed by multi-year in situ physiological measurements","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2022-07-14 14:29:10","doi":"10.21203/rs.3.rs-1821506/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"","date":"2022-07-08T10:45:22+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2022-07-06T12:15:32+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2022-07-05T14:37:18+00:00","index":"","fulltext":""},{"type":"submitted","content":"Oecologia","date":"2022-07-03T16:47:29+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"oecologia","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"oeco","sideBox":"Learn more about [Oecologia](https://www.springer.com/journal/442)","snPcode":"442","submissionUrl":"https://submission.nature.com/new-submission/442/3","title":"Oecologia","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"82d7ee2a-6d3e-4cb1-9dd2-7562fd3d7ff4","owner":[],"postedDate":"July 14th, 2022","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2023-10-16T18:35:46+00:00","versionOfRecord":{"articleIdentity":"rs-1821506","link":"https://doi.org/10.1007/s00442-023-05326-9","journal":{"identity":"oecologia","isVorOnly":false,"title":"Oecologia"},"publishedOn":"2023-01-24 18:30:15","publishedOnDateReadable":"January 24th, 2023"},"versionCreatedAt":"2022-07-14 14:29:10","video":"","vorDoi":"10.1007/s00442-023-05326-9","vorDoiUrl":"https://doi.org/10.1007/s00442-023-05326-9","workflowStages":[]},"version":"v1","identity":"rs-1821506","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-1821506","identity":"rs-1821506","version":["v1"]},"buildId":"_2-kVJe1T_tPrBINL-cwx","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}