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Thermal effects on light harvesting in an endemic southern African seagrass, Zostera capensis
Thesis (MSc)--Stellenbosch University, 2022.
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| Format: | Thesis |
| Language: | en_ZA |
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Stellenbosch : Stellenbosch University
2022
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| _version_ | 1867614032177922048 |
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| access_status_str | Open Access |
| author | Yuill, Jessie Joanne Margaret |
| author2 | Midgley, Guy F. |
| author_browse | Midgley, Guy F. Yuill, Jessie Joanne Margaret |
| author_facet | Midgley, Guy F. Yuill, Jessie Joanne Margaret |
| author_sort | Yuill, Jessie Joanne Margaret |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Thesis (MSc)--Stellenbosch University, 2022. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/125022 |
| institution | Stellenbosch University (South Africa) |
| language | en_ZA |
| last_indexed | 2026-06-10T12:45:35.384Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2022 |
| publishDateRange | 2022 |
| publishDateSort | 2022 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/125022 Thermal effects on light harvesting in an endemic southern African seagrass, Zostera capensis Yuill, Jessie Joanne Margaret Midgley, Guy F. Von der Heyden, Sophie Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology. Seagrasses -- South Africa Zosteraceae -- Geographical distribution Zostera capensis -- South Africa Seagrasses -- Effect of temperature on Seagrasses -- Effect of light on Zostera capensis -- Effect of light on Light harvesting Photosynthetic efficiency Climatic changes UCTD Thesis (MSc)--Stellenbosch University, 2022. ENGLISH ABSTRACT: This study investigated the effect of temperature on light harvesting characteristics of an endemic south African seagrass, Zostera capensis Setch., and its resilience to warming, in the context of its wide bioregional range. This range covers four bioregions, namely cool temperate, warm temperate, subtropical and tropical, with a differential in mean sea surface temperature of almost 15°C from West to East. Temperature has long been recognized as a driver of photosynthesis, one of the most temperature sensitive physiological processes within plants, and species under strong temperature control are potentially vulnerable to temperature change if they lack plasticity in thermal response. Most terrestrial plants show some plasticity to growth temperature, such as seasonal shifts, and such acclimation may be crucial in allowing Z. capensis to maintain photosynthesis under differing temperature regimes. With projected changes in sea surface temperatures, and increases in marine heat wave intensity and frequency, understanding the thermal plasticity and tolerance of Z. capensis will inform the need for adaptation and mitigation measures to reduce risks to this species and the ecosystem services it provides. This study therefore tested the main hypotheses that this species’ biogeographical range is achieved through locally thermally acclimated populations, due to 1) bioregional shifts in the temperature for optimal light harvesting, and 2) relatively greater tolerance of acute warming events in tropical populations. Two experiments were conducted, the first testing for bioregional differences in thermal response of light harvesting characteristics of Z. capensis in the field, and the second for longer term heat wave and acclimatory responses under controlled environment conditions. Quantification of light harvesting characteristics under short-term temperature exposure to 20°C, 25°C and 30°C showed that individuals from cooler ranges (cool and warm temperate locations) were higher in photosynthetic efficiency compared to the individuals from the two warmer bioregions, but almost all individuals showed significantly decreased photosynthetic efficiency at 30°C. Individuals from the warmest tropical bioregion were an exception, and their efficiencies were reduced under all three temperatures. When grown under common- garden conditions of 20°C for 4 weeks, individuals from all the bioregions acclimated similarly, with optimum light harvesting found to occur at 20°C. Following this acclimation period of 4 weeks, an acute experimental heat wave resulted in all populations maintaining high levels of efficiency throughout the treatment, but with site specific differences in quenching metrics. The results of this study therefore show that that, cool edge, central temperate and subtropical, and warm edge populations displayed similar light harvesting thermal response characteristics under field conditions, with the exception of the tropical individuals whose efficiency was reduced regardless of temperature. All individuals showed similar thermal acclimation response under controlled cool conditions, but their responses to acute warming contrasted with a priori expectations based on their biogeographical provenances. This similarity in short term and acclimatory temperature response across the biogeographical range of the species indicates a relative lack of thermal plasticity in Z. capensis, and suggests a strong tropical thermal limit. AFRIKAANSE OPSOMMING: Hierdie studie het die effek van temperatuur op fotosintese van 'n endemiese Suid-Afrikaanse seegras, Zostera capensis Setch., en sy weerstand teen verwarming, in die konteks van sy wye biostreekgebied ondersoek. Hierdie gebied dek vier biostreke, naamlik koel gematigd, warm gematigd, subtropies en tropies, met 'n verskil in gemiddelde see-oppervlaktemperatuur van byna 15°C van Wes na Oos. Temperatuur is lank reeds erken as 'n drywer van fotosintese, een van die mees temperatuursensitiewe fisiologiese prosesse vir plante, en spesies onder sterk temperatuurbeheer is potensieel kwesbaar vir temperatuurverandering as hulle nie termiese plastisiteit kan toon nie. Die meeste landplante toon 'n mate van plastisiteit teenoor groeitemperatuur, soos seisoenale verskuiwings, en sulke akklimatisering kan noodsaaklik wees om Z. capensis toe te laat om fotosintese onder verskillende temperatuurregimes te handhaaf. Met geprojekteerde veranderinge in see-oppervlaktemperature, en toenames in mariene hittegolfintensiteit en -frekwensie, sal begrip van die termiese plastisiteit en verdraagsaamheid van Z. capensis die behoefte aan aanpassing en versagtingsmaatreëls inlig om risiko's vir hierdie spesie en die ekosisteemdienste wat dit verskaf te verminder. Hierdie studie het dus die hoofhipoteses getoets dat hierdie spesie se biogeografiese omvang bereik word deur plaaslik termies geakklimatiseerde populasies, as gevolg van 1) biostreekverskuiwings in die temperatuur vir optimale fotosintese, en 2) relatief groter toleransie van akute opwarmingsgebeure in tropiese populasies. Twee eksperimente is uitgevoer, die eerste het getoets vir biostreeksverskille in termiese reaksie van lig-oes eienskappe van Z. capensis in die veld, en die tweede vir langer termyn hittegolf en akklimatoriese reaksies onder beheerde omgewingstoestande. Kwantifisering van lig-oes eienskappe onder korttermyn temperatuur blootstelling aan 20°C, 25°C en 30°C het getoon dat individue van koeler gebiede (koel en warm gematigde liggings) hoër in fotosintetiese doeltreffendheid was in vergelyking met die individue van die twee warmer biostreke, maar byna alle individue het aansienlik verminderde fotosintetiese doeltreffendheid by 30°C getoon. Individue van die warmste tropiese biostreek was 'n uitsondering, en hul doeltreffendheid is verminder onder al drie temperature. Wanneer dit vir 4 weke onder gewone tuintoestande van 20°C gekweek is, het individue van al die biostreke soortgelyk geakklimatiseer, met optimale ligte oes wat by 20°C gevind is. Na hierdie akklimatiseringsperiode van 4 weke, het 'n akute eksperimentele hittegolf daartoe gelei dat alle bevolkings hoë vlakke van doeltreffendheid regdeur die behandeling gehandhaaf het, maar met plekspesifieke verskille in blusmetrieke. Die resultate van hierdie studie toon dus dat koelrand-, sentrale gematigde en subtropiese en warmrandpopulasies soortgelyke termiese reaksie-eienskappe van ligoes onder veldtoestande vertoon het, met die uitsondering van die tropiese individue wie se doeltreffendheid verminder is ongeag temperatuur. Alle individue het soortgelyke termiese akklimatiseringsreaksie getoon onder beheerde koel toestande, maar hul reaksies op akute verwarming het gekontrasteer met a priori verwagtinge gebaseer op hul biogeografiese herkoms. Hierdie ooreenkoms in korttermyn- en akklimatoire temperatuurrespons oor die biogeografiese omvang van die spesie dui op 'n relatiewe gebrek aan termiese plastisiteit in Z. capensis, en dui op 'n sterk tropiese termiese limiet. Masters 2022-02-04T08:43:12Z 2022-04-29T12:50:45Z 2022-08-18T03:00:12Z 2022-04 Thesis http://hdl.handle.net/10019.1/125022 en_ZA Stellenbosch University 71 pages : illustrations (some color), maps application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Seagrasses -- South Africa Zosteraceae -- Geographical distribution Zostera capensis -- South Africa Seagrasses -- Effect of temperature on Seagrasses -- Effect of light on Zostera capensis -- Effect of light on Light harvesting Photosynthetic efficiency Climatic changes UCTD Yuill, Jessie Joanne Margaret Thermal effects on light harvesting in an endemic southern African seagrass, Zostera capensis |
| title | Thermal effects on light harvesting in an endemic southern African seagrass, Zostera capensis |
| title_full | Thermal effects on light harvesting in an endemic southern African seagrass, Zostera capensis |
| title_fullStr | Thermal effects on light harvesting in an endemic southern African seagrass, Zostera capensis |
| title_full_unstemmed | Thermal effects on light harvesting in an endemic southern African seagrass, Zostera capensis |
| title_short | Thermal effects on light harvesting in an endemic southern African seagrass, Zostera capensis |
| title_sort | thermal effects on light harvesting in an endemic southern african seagrass zostera capensis |
| topic | Seagrasses -- South Africa Zosteraceae -- Geographical distribution Zostera capensis -- South Africa Seagrasses -- Effect of temperature on Seagrasses -- Effect of light on Zostera capensis -- Effect of light on Light harvesting Photosynthetic efficiency Climatic changes UCTD |
| url | http://hdl.handle.net/10019.1/125022 |
| work_keys_str_mv | AT yuilljessiejoannemargaret thermaleffectsonlightharvestinginanendemicsouthernafricanseagrasszosteracapensis |