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The physiological importance of small leaf sizes in the mediterranean type ecosystem vegetation of the Cape floristic region
Numerous "Fynbos" species of the Cape Floristic Region (CFR) have particularly fine, narrow leaves. The rates of transpiration and heat loss are partially dependent on boundary layer conductance, which is determined by leaf shape and size, surface modifications and wind speed. We expected fine-leave...
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| Format: | Thesis |
| Language: | English |
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Department of Biological Sciences
2017
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| _version_ | 1867613140711112704 |
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| access_status_str | Open Access |
| author | Yates, Megan |
| author2 | Cramer, Michael D |
| author_browse | Cramer, Michael D Yates, Megan |
| author_facet | Cramer, Michael D Yates, Megan |
| author_sort | Yates, Megan |
| collection | Thesis |
| description | Numerous "Fynbos" species of the Cape Floristic Region (CFR) have particularly fine, narrow leaves. The rates of transpiration and heat loss are partially dependent on boundary layer conductance, which is determined by leaf shape and size, surface modifications and wind speed. We expected fine-leaved species with higher boundary layer conductance to transpire faster than broad-leaved species at low temperatures whereas at higher temperatures we expected transpiration to be limited by stomata! conductance. In contrast, the rate of heat loss may be constrained by thick boundary layers in larger leaves at high temperatures. Leaf gas exchange characteristics at various temperatures were correlated with boundary layer thickness, leaf area and specific leaf area for 14 Proteaceae species using phylogenetically independent contrast species. When the temperatures of individual leaves were altered, while ambient temperature was kept at l 8°C, water loss decreased significantly at both 12°C and 30°C with increased leaf size and thus boundary layer thickness. At 30°C, small leaves with thin boundary layers resulted in leaf temperatures below ambient, while larger leaves with thicker boundary layers had leaf temperatures closer to ambient. However, at 30°C the variation in leaf temperature between the smallest and largest leaves was only 3.4°C. Such a small variation in leaf temperature is unlikely to alter temperature-dependent physiological processes. We conclude that the small boundary layer associated with small leaves enables fine-leaved species to transpire at faster rates when water is plentiful. This may be a particularly important strategy for plants that take up most of their nutrients in the wet winter months from nutrient-poor highly leached soils of the CFR region. We suggest that fine leaves are an adaptation for nutrient uptake during winter, although they may also have the benefit of improved coupling of leaf to ambient temperature during the summer drought period. |
| format | Thesis |
| id | oai:open.uct.ac.za:11427/26302 |
| institution | University of Cape Town (South Africa) |
| language | eng |
| last_indexed | 2026-06-10T12:31:24.573Z |
| license_str | Not specified — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UCTD — University of Cape Town Open Access Repository |
| publishDate | 2017 |
| publishDateRange | 2017 |
| publishDateSort | 2017 |
| publisher | Department of Biological Sciences |
| publisherStr | Department of Biological Sciences |
| record_format | dspace |
| source_str | UCTD — University of Cape Town Open Access Repository |
| spelling | oai:open.uct.ac.za:11427/26302 The physiological importance of small leaf sizes in the mediterranean type ecosystem vegetation of the Cape floristic region Yates, Megan Cramer, Michael D Botany Ecosystems Numerous "Fynbos" species of the Cape Floristic Region (CFR) have particularly fine, narrow leaves. The rates of transpiration and heat loss are partially dependent on boundary layer conductance, which is determined by leaf shape and size, surface modifications and wind speed. We expected fine-leaved species with higher boundary layer conductance to transpire faster than broad-leaved species at low temperatures whereas at higher temperatures we expected transpiration to be limited by stomata! conductance. In contrast, the rate of heat loss may be constrained by thick boundary layers in larger leaves at high temperatures. Leaf gas exchange characteristics at various temperatures were correlated with boundary layer thickness, leaf area and specific leaf area for 14 Proteaceae species using phylogenetically independent contrast species. When the temperatures of individual leaves were altered, while ambient temperature was kept at l 8°C, water loss decreased significantly at both 12°C and 30°C with increased leaf size and thus boundary layer thickness. At 30°C, small leaves with thin boundary layers resulted in leaf temperatures below ambient, while larger leaves with thicker boundary layers had leaf temperatures closer to ambient. However, at 30°C the variation in leaf temperature between the smallest and largest leaves was only 3.4°C. Such a small variation in leaf temperature is unlikely to alter temperature-dependent physiological processes. We conclude that the small boundary layer associated with small leaves enables fine-leaved species to transpire at faster rates when water is plentiful. This may be a particularly important strategy for plants that take up most of their nutrients in the wet winter months from nutrient-poor highly leached soils of the CFR region. We suggest that fine leaves are an adaptation for nutrient uptake during winter, although they may also have the benefit of improved coupling of leaf to ambient temperature during the summer drought period. 2017-11-16T07:12:58Z 2017-11-16T07:12:58Z 2007 2017-02-02T13:42:51Z Bachelor Thesis Honours BSc (Hons) http://hdl.handle.net/11427/26302 eng application/pdf Department of Biological Sciences Faculty of Science University of Cape Town |
| spellingShingle | Botany Ecosystems Yates, Megan The physiological importance of small leaf sizes in the mediterranean type ecosystem vegetation of the Cape floristic region |
| thesis_degree_str | Bachelor's / Honours |
| title | The physiological importance of small leaf sizes in the mediterranean type ecosystem vegetation of the Cape floristic region |
| title_full | The physiological importance of small leaf sizes in the mediterranean type ecosystem vegetation of the Cape floristic region |
| title_fullStr | The physiological importance of small leaf sizes in the mediterranean type ecosystem vegetation of the Cape floristic region |
| title_full_unstemmed | The physiological importance of small leaf sizes in the mediterranean type ecosystem vegetation of the Cape floristic region |
| title_short | The physiological importance of small leaf sizes in the mediterranean type ecosystem vegetation of the Cape floristic region |
| title_sort | physiological importance of small leaf sizes in the mediterranean type ecosystem vegetation of the cape floristic region |
| topic | Botany Ecosystems |
| url | http://hdl.handle.net/11427/26302 |
| work_keys_str_mv | AT yatesmegan thephysiologicalimportanceofsmallleafsizesinthemediterraneantypeecosystemvegetationofthecapefloristicregion AT yatesmegan physiologicalimportanceofsmallleafsizesinthemediterraneantypeecosystemvegetationofthecapefloristicregion |