Exploring the impact of sub-ambient CO2 concentrations on Oxalis growth: implications for food sustainability among Pleistocene human foragers in the Greater Cape Floristic Region
- Authors: Faltein-Maqubela, Zintle
- Date: 2025-04-02
- Subjects: Carbon dioxide Thermal properties , Geophyte , Hunting and gathering societies Pleistocene , Paleobotany Pleistocene , Oxalis , Prehistoric peoples Food , Cape Floristic Kingdom
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/479097 , vital:78260
- Description: Humans inhabiting the glacial refugia of the Cape Floristic Region during the Middle Pleistocene are believed to have relied on underground storage organs (USOs) as a crucial carbohydrate source. While previous research has highlighted the nutritional potential of these plants for early human gatherers, such studies are typically conducted under modern climatic conditions and do not account for the reduced plant productivity and USO yields associated with the lower atmospheric CO₂ concentrations characteristic of Pleistocene glacial periods. To evaluate the impact of CO₂ availability on plant productivity, I cultivated two Oxalis species—O. pes-caprae and O. punctata, both known to have been harvested by early foragers—under CO₂ concentrations ranging from 180 ppm to 400 ppm. Results showed that glacial-level CO₂ concentrations significantly reduced bulb production in O. pes-caprae and photosynthetic rates in both species. Using these findings to model Pleistocene foraging behaviour, I estimate that human foragers would have needed to spend an additional 8 hours gathering food to meet their daily dietary requirements of 2000 calories, suggesting the need for alternative food sources to supplement their diet. These findings emphasise the importance of considering historical plant growth conditions, particularly atmospheric CO₂ levels, when reconstructing past human diets. Failure to account for these factors may represent a significant gap in our understanding of human subsistence strategies during glacial periods. , Thesis (MSc) -- Faculty of Science, Botany, 2025
- Full Text:
- Authors: Faltein-Maqubela, Zintle
- Date: 2025-04-02
- Subjects: Carbon dioxide Thermal properties , Geophyte , Hunting and gathering societies Pleistocene , Paleobotany Pleistocene , Oxalis , Prehistoric peoples Food , Cape Floristic Kingdom
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/479097 , vital:78260
- Description: Humans inhabiting the glacial refugia of the Cape Floristic Region during the Middle Pleistocene are believed to have relied on underground storage organs (USOs) as a crucial carbohydrate source. While previous research has highlighted the nutritional potential of these plants for early human gatherers, such studies are typically conducted under modern climatic conditions and do not account for the reduced plant productivity and USO yields associated with the lower atmospheric CO₂ concentrations characteristic of Pleistocene glacial periods. To evaluate the impact of CO₂ availability on plant productivity, I cultivated two Oxalis species—O. pes-caprae and O. punctata, both known to have been harvested by early foragers—under CO₂ concentrations ranging from 180 ppm to 400 ppm. Results showed that glacial-level CO₂ concentrations significantly reduced bulb production in O. pes-caprae and photosynthetic rates in both species. Using these findings to model Pleistocene foraging behaviour, I estimate that human foragers would have needed to spend an additional 8 hours gathering food to meet their daily dietary requirements of 2000 calories, suggesting the need for alternative food sources to supplement their diet. These findings emphasise the importance of considering historical plant growth conditions, particularly atmospheric CO₂ levels, when reconstructing past human diets. Failure to account for these factors may represent a significant gap in our understanding of human subsistence strategies during glacial periods. , Thesis (MSc) -- Faculty of Science, Botany, 2025
- Full Text:
Carnivory submerged: aspects of the ecology and ecophysiology of the aquatic Utricularia stellaris L. fil. (Lentibulariaceae) in South Africa
- Authors: Marais, Alice-Jane
- Date: 2024-10-11
- Subjects: Submerged aquatic vegetation , Bladderworts South Africa , Carnivorous plants , Bladderworts Ecology , Bladderworts Ecophysiology , Plant-microbe relationships
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/464473 , vital:76514
- Description: The trapping structures produced by aquatic species of Utricularia have traditionally been interpreted to function as adaptations to capture and break down zooplankton prey, as in other carnivorous plants, to overcome nutrient limitations. However, an increasing number of studies have found that these plants may also rely on benefits derived from living mutualistic microbial communities contained within traps. This study documents aspects of the environmental, growth and physiological characteristics of U. stellaris to inform and to form a basis for future investigation into the plant-microbe interaction. The environmental conditions in which U. stellaris grows were documented to identify potential adverse conditions plants are subject to in situ, from which nutrient limitation was identified as a primary limitation. Plant growth and trapping structures were then assessed to identify possible adaptations of plants to overcome these limitations. The production of trapping structures likely constitutes an adaptive trait, with 30% of total biomass per node allocated to the production of these structures. Based on their capture function, traps may aid plants based on their contents, possibly supplementing plants with nutrients. Although assessments of the habitats of U. stellaris indicate that dissolved CO₂ concentrations in the ambient water are high, CO₂ may still be limiting to the photosynthetic rates of these plants due to viscous water resisting the diffusion of CO₂. The primary site of photosynthesis in U. stellaris is leaves and trap tissue’s contribution to photosynthetic output is negligible. U. stellaris plants are subject to CO₂ limitations in natural pond conditions, making the substantial allocation of resources to non-photosynthetic trapping tissue even more costly. Therefore, benefits gained from trapping structures are likely to be derived from trap contents; having ruled out the possibility that the trap tissue itself is photosynthetic. Trap contents of U. stellaris were assessed. The proportion of traps containing living microbial communities greatly exceeded the proportion containing zooplankton prey. In addition, these communities were found to be diverse, stable, and self-sustaining. These results suggest that trapping structures may be beneficial for both the carnivorous capture of prey and the housing of living microbial communities. These results indicate the plantmicrobe interaction in U. stellaris warrants further study. , Thesis (MSc) -- Faculty of Science, Botany, 2024
- Full Text:
- Authors: Marais, Alice-Jane
- Date: 2024-10-11
- Subjects: Submerged aquatic vegetation , Bladderworts South Africa , Carnivorous plants , Bladderworts Ecology , Bladderworts Ecophysiology , Plant-microbe relationships
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/464473 , vital:76514
- Description: The trapping structures produced by aquatic species of Utricularia have traditionally been interpreted to function as adaptations to capture and break down zooplankton prey, as in other carnivorous plants, to overcome nutrient limitations. However, an increasing number of studies have found that these plants may also rely on benefits derived from living mutualistic microbial communities contained within traps. This study documents aspects of the environmental, growth and physiological characteristics of U. stellaris to inform and to form a basis for future investigation into the plant-microbe interaction. The environmental conditions in which U. stellaris grows were documented to identify potential adverse conditions plants are subject to in situ, from which nutrient limitation was identified as a primary limitation. Plant growth and trapping structures were then assessed to identify possible adaptations of plants to overcome these limitations. The production of trapping structures likely constitutes an adaptive trait, with 30% of total biomass per node allocated to the production of these structures. Based on their capture function, traps may aid plants based on their contents, possibly supplementing plants with nutrients. Although assessments of the habitats of U. stellaris indicate that dissolved CO₂ concentrations in the ambient water are high, CO₂ may still be limiting to the photosynthetic rates of these plants due to viscous water resisting the diffusion of CO₂. The primary site of photosynthesis in U. stellaris is leaves and trap tissue’s contribution to photosynthetic output is negligible. U. stellaris plants are subject to CO₂ limitations in natural pond conditions, making the substantial allocation of resources to non-photosynthetic trapping tissue even more costly. Therefore, benefits gained from trapping structures are likely to be derived from trap contents; having ruled out the possibility that the trap tissue itself is photosynthetic. Trap contents of U. stellaris were assessed. The proportion of traps containing living microbial communities greatly exceeded the proportion containing zooplankton prey. In addition, these communities were found to be diverse, stable, and self-sustaining. These results suggest that trapping structures may be beneficial for both the carnivorous capture of prey and the housing of living microbial communities. These results indicate the plantmicrobe interaction in U. stellaris warrants further study. , Thesis (MSc) -- Faculty of Science, Botany, 2024
- Full Text:
Encroaching species are stronger anisohydric “water spenders” under elevated CO2 conditions: implications for savanna seedling establishment rates
- Authors: Reynolds, Liam Macleod
- Date: 2024-10-11
- Subjects: Xylem , Scrub encroachment , Isotopes , Photosynthesis , Plants Effect of atmospheric carbon dioxide on
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/465091 , vital:76572
- Description: Plant water transport systems play a fundamental role in the productivity and survival of terrestrial plants due to the vascular architecture placing a physical limit on metabolic function. Savannas have high variability in rainfall, leading multiple studies to suggest that plant water-use strategies are key mechanisms affecting seedling establishment rates. Many savannas are seeing a directional shift towards an increase in the abundance of certain woody species through a process known as bush encroachment, which has been largely attributed to the fertilising effect of rising atmospheric [CO2] on C3 trees. These species are classified as encroachers. While there have been multiple studies investigating changes in the physiology of savanna species under elevated CO2 (eCO2), few have examined how climate and eCO2 affects the fundamental water-use strategies in the seedling stage, a crucial demographic bottleneck. Here, this research provides valuable insights into the mechanisms behind bush encroachment in the context of eCO2 using results from a pot experiment at the Rhodes University Elevated CO2 facility and a field experiment. All species showed water use strategies characteristic of anisohydric “water-spenders”, however, the vulnerability to embolism and rates of water-use were different between encroachers and non-encroachers. Encroachers are better at taking advantage of water pulses, particularly under eCO2 and grass competition. This comes at the cost of higher xylem vulnerability during drought, leading to reductions in conductance when exposed to heavy water stress. The response of the photosynthetic parameters mirrored this, with encroaching species had higher rates of photosynthesis and photosystem II quantum yield than non-encroachers under the well-watered treatments. Field experiments revealed that small trees are particularly vulnerable to drought stress, when compared to medium and large trees. The outcomes of this complex response will largely depend on the extent of changes to biotic and abiotic factors across spatial and temporal zones caused by climate change. This research highlights potential hydraulic mechanisms contributing to the increase in bush encroachment, as well as providing important insights into the determinant factors that make a savanna species capable of encroachment. , Thesis (MSc) -- Faculty of Science, Botany, 2024
- Full Text:
- Authors: Reynolds, Liam Macleod
- Date: 2024-10-11
- Subjects: Xylem , Scrub encroachment , Isotopes , Photosynthesis , Plants Effect of atmospheric carbon dioxide on
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/465091 , vital:76572
- Description: Plant water transport systems play a fundamental role in the productivity and survival of terrestrial plants due to the vascular architecture placing a physical limit on metabolic function. Savannas have high variability in rainfall, leading multiple studies to suggest that plant water-use strategies are key mechanisms affecting seedling establishment rates. Many savannas are seeing a directional shift towards an increase in the abundance of certain woody species through a process known as bush encroachment, which has been largely attributed to the fertilising effect of rising atmospheric [CO2] on C3 trees. These species are classified as encroachers. While there have been multiple studies investigating changes in the physiology of savanna species under elevated CO2 (eCO2), few have examined how climate and eCO2 affects the fundamental water-use strategies in the seedling stage, a crucial demographic bottleneck. Here, this research provides valuable insights into the mechanisms behind bush encroachment in the context of eCO2 using results from a pot experiment at the Rhodes University Elevated CO2 facility and a field experiment. All species showed water use strategies characteristic of anisohydric “water-spenders”, however, the vulnerability to embolism and rates of water-use were different between encroachers and non-encroachers. Encroachers are better at taking advantage of water pulses, particularly under eCO2 and grass competition. This comes at the cost of higher xylem vulnerability during drought, leading to reductions in conductance when exposed to heavy water stress. The response of the photosynthetic parameters mirrored this, with encroaching species had higher rates of photosynthesis and photosystem II quantum yield than non-encroachers under the well-watered treatments. Field experiments revealed that small trees are particularly vulnerable to drought stress, when compared to medium and large trees. The outcomes of this complex response will largely depend on the extent of changes to biotic and abiotic factors across spatial and temporal zones caused by climate change. This research highlights potential hydraulic mechanisms contributing to the increase in bush encroachment, as well as providing important insights into the determinant factors that make a savanna species capable of encroachment. , Thesis (MSc) -- Faculty of Science, Botany, 2024
- Full Text:
Evaluating the physiological, morphological and nutritional effects of elevated atmospheric CO2 and drought on select South African maize cultivars
- Authors: Bopape, Tebadi Mamadiga
- Date: 2021-10
- Subjects: Corn Varieties South Africa , Dry farming South Africa , Corn Effect of atmospheric carbon dioxide on South Africa , Corn Effect of drought on South Africa , Corn Morphology , Corn Nutrition , Corn Physiological effect
- Language: English
- Type: Master theses , text
- Identifier: http://hdl.handle.net/10962/189020 , vital:44807
- Description: Thesis embargoed. Expected Release date October 2022. , Thesis (MSc) -- Faculty of Science, Botany, 2021
- Full Text:
- Authors: Bopape, Tebadi Mamadiga
- Date: 2021-10
- Subjects: Corn Varieties South Africa , Dry farming South Africa , Corn Effect of atmospheric carbon dioxide on South Africa , Corn Effect of drought on South Africa , Corn Morphology , Corn Nutrition , Corn Physiological effect
- Language: English
- Type: Master theses , text
- Identifier: http://hdl.handle.net/10962/189020 , vital:44807
- Description: Thesis embargoed. Expected Release date October 2022. , Thesis (MSc) -- Faculty of Science, Botany, 2021
- Full Text:
The effects of elevated atmospheric CO2 on the biological control of invasive aquatic weeds in South Africa
- Authors: Baso, Nompumelelo Catherine
- Date: 2020
- Subjects: Aquatic weeds -- Biological control -- South Africa , Plants -- Effect of atmospheric carbon dioxide on , Atmospheric carbon dioxide -- Environmental aspects
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/140772 , vital:37917
- Description: There has been a rapid increase in atmospheric CO2 concentration, from pre-industrial values of 280 ppm to more than 400 ppm currently, and this is expected to more than double by the end of the 21st century. Studies have shown that plants grown above 600 ppm tend to have an increased growth rate and invest more in carbon-based defences. This has important implications for the management of invasive alien plants, especially for the field of biological control which is mostly dependent on herbivorous insects. This is because insects reared on such plants have been shown to have reduced overall fitness. Nevertheless, most of the studies on potential changes in plant-insect interactions under elevated CO2 are based on agricultural systems, with only a limited number of these types of studies conducted on alien invasive weeds. However, climate change and invasive species are two of the most prevalent features of global environmental change. Therefore, this also warrants active research and experimental studies to better understand how these systems will be affected by future climates. Thus, the aim of this study was to investigate the effects of elevated atmospheric CO2 on the biological control of four invasive aquatic weeds (Azolla filiculoides, Salvinia molesta, Pistia stratiotes, and Myriophyllum aquaticum). These species are a threat to natural resources in South Africa but are currently under successful control by their biological control agents (Stenopelmus rufinasus, Cyrtobagous salviniae, Neohydronomus affinis, and Lysathia n. sp.). To achieve this, the selected plant species were grown in a three-factor experimental design in winter (CO2 X nutrients X herbivory), and another two-factorial design in summer (CO2 X herbivory). Atmospheric CO2 concentrations were set at ambient (400 ppm) or elevated (800 ppm), as per the predictions of the IPCC. As per my hypothesis, the results suggest that these species will become more challenging in future due to increased biomass production, asexual reproduction and a higher C: N ratio which is evident under high CO2 concentrations. Although the biological control agents were in some instances able to reduce this CO2 fertilisation effect, their efficacy was significantly reduced compared with the levels of control observed at ambient CO2. These results suggest that additional biological control agents and other management methods may be needed for continued control of these invasive macrophytes, both in South Africa and further afield where they are problematic.
- Full Text:
- Authors: Baso, Nompumelelo Catherine
- Date: 2020
- Subjects: Aquatic weeds -- Biological control -- South Africa , Plants -- Effect of atmospheric carbon dioxide on , Atmospheric carbon dioxide -- Environmental aspects
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/140772 , vital:37917
- Description: There has been a rapid increase in atmospheric CO2 concentration, from pre-industrial values of 280 ppm to more than 400 ppm currently, and this is expected to more than double by the end of the 21st century. Studies have shown that plants grown above 600 ppm tend to have an increased growth rate and invest more in carbon-based defences. This has important implications for the management of invasive alien plants, especially for the field of biological control which is mostly dependent on herbivorous insects. This is because insects reared on such plants have been shown to have reduced overall fitness. Nevertheless, most of the studies on potential changes in plant-insect interactions under elevated CO2 are based on agricultural systems, with only a limited number of these types of studies conducted on alien invasive weeds. However, climate change and invasive species are two of the most prevalent features of global environmental change. Therefore, this also warrants active research and experimental studies to better understand how these systems will be affected by future climates. Thus, the aim of this study was to investigate the effects of elevated atmospheric CO2 on the biological control of four invasive aquatic weeds (Azolla filiculoides, Salvinia molesta, Pistia stratiotes, and Myriophyllum aquaticum). These species are a threat to natural resources in South Africa but are currently under successful control by their biological control agents (Stenopelmus rufinasus, Cyrtobagous salviniae, Neohydronomus affinis, and Lysathia n. sp.). To achieve this, the selected plant species were grown in a three-factor experimental design in winter (CO2 X nutrients X herbivory), and another two-factorial design in summer (CO2 X herbivory). Atmospheric CO2 concentrations were set at ambient (400 ppm) or elevated (800 ppm), as per the predictions of the IPCC. As per my hypothesis, the results suggest that these species will become more challenging in future due to increased biomass production, asexual reproduction and a higher C: N ratio which is evident under high CO2 concentrations. Although the biological control agents were in some instances able to reduce this CO2 fertilisation effect, their efficacy was significantly reduced compared with the levels of control observed at ambient CO2. These results suggest that additional biological control agents and other management methods may be needed for continued control of these invasive macrophytes, both in South Africa and further afield where they are problematic.
- Full Text:
Woody plant encroachment in arid and mesic South African savanna-grasslands: same picture, different story?
- Authors: Skowno, Andrew Luke
- Date: 2018
- Subjects: Savanna ecology South Africa Eastern Cape , Remote sensing , Woody plants South Africa Eastern Cape , Grasslands South Africa Eastern Cape , Plant invasions South Africa Eastern Cape
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/62603 , vital:28212
- Description: Woody plant encroachment in South Africa’s savanna-grasslands has been considered a rangeland management problem since the early 1900s. This phenomenon, which has been observed globally, is particularly important in Africa given the extent of tropical grassy biomes on the continent and their importance for rural livelihoods. In this study, local and regional scale approaches were used to investigate woody cover change in South Africa across the important savanna-grassland rainfall threshold of 650 mm mean annual precipitation (MAP). The aim was to test this threshold using remote sensing and demographic surveys in order to better understand the patterns, mechanisms and drivers of encroachment. Rates of encroachment and population demographics of Vachelia karroo were compared at arid and mesic savanna sites in the Eastern Cape, using time-series analysis of historical aerial photographs in conjunction with field surveys. Changes in the extent of woodland vs. grassland were then quantified at a national scale (1990-2013) by combining optical and synthetic aperture radar remote sensing data. This produced the first map of woodland- grassland shifts for South Africa and provided the basis for a spatially explicit investigation of the key drivers of change. The local studies revealed higher rates of encroachment at mesic sites than at arid sites, with a correlation between drought and rate of encroachment at the arid site. Vachelia karroo seedlings and stunted saplings were more prevalent at mesic sites than at arid sites and the growth form of adult trees differed significantly between sites. The national remote sensing investigation showed that woodland replaced grassland in over 5% of South Africa’s savanna- grasslands between 1990 and 2014, at rates consistent with other global and regional studies. Spatially explicit models showed a pattern of incremental expansion of woodland along a ‘tree front’ and complex relationships between woodland increase and fire, rainfall, terrain ruggedness and temperature. Overall, the local and regional scale findings of this work highlight the importance of the savanna rainfall threshold (~650 mm MAP) and the presence / absence of fire in understanding savanna dynamics and woody cover change in the context of global drivers such as elevated atmospheric CO2.
- Full Text:
- Authors: Skowno, Andrew Luke
- Date: 2018
- Subjects: Savanna ecology South Africa Eastern Cape , Remote sensing , Woody plants South Africa Eastern Cape , Grasslands South Africa Eastern Cape , Plant invasions South Africa Eastern Cape
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/62603 , vital:28212
- Description: Woody plant encroachment in South Africa’s savanna-grasslands has been considered a rangeland management problem since the early 1900s. This phenomenon, which has been observed globally, is particularly important in Africa given the extent of tropical grassy biomes on the continent and their importance for rural livelihoods. In this study, local and regional scale approaches were used to investigate woody cover change in South Africa across the important savanna-grassland rainfall threshold of 650 mm mean annual precipitation (MAP). The aim was to test this threshold using remote sensing and demographic surveys in order to better understand the patterns, mechanisms and drivers of encroachment. Rates of encroachment and population demographics of Vachelia karroo were compared at arid and mesic savanna sites in the Eastern Cape, using time-series analysis of historical aerial photographs in conjunction with field surveys. Changes in the extent of woodland vs. grassland were then quantified at a national scale (1990-2013) by combining optical and synthetic aperture radar remote sensing data. This produced the first map of woodland- grassland shifts for South Africa and provided the basis for a spatially explicit investigation of the key drivers of change. The local studies revealed higher rates of encroachment at mesic sites than at arid sites, with a correlation between drought and rate of encroachment at the arid site. Vachelia karroo seedlings and stunted saplings were more prevalent at mesic sites than at arid sites and the growth form of adult trees differed significantly between sites. The national remote sensing investigation showed that woodland replaced grassland in over 5% of South Africa’s savanna- grasslands between 1990 and 2014, at rates consistent with other global and regional studies. Spatially explicit models showed a pattern of incremental expansion of woodland along a ‘tree front’ and complex relationships between woodland increase and fire, rainfall, terrain ruggedness and temperature. Overall, the local and regional scale findings of this work highlight the importance of the savanna rainfall threshold (~650 mm MAP) and the presence / absence of fire in understanding savanna dynamics and woody cover change in the context of global drivers such as elevated atmospheric CO2.
- Full Text:
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