Mild experimental climate warming induces metabolic impairment and massive mortalities in southern African quartz field succulents |
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| Authors: | CF Musil PDR Van Heerden CD Cilliers U Schmiedel |
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| Institution: | 1. Climate Change and Bio-Adaptation Division, South African National Biodiversity Institute, Private Bag X7, Claremont 7735, South Africa;2. School of Environmental Sciences and Development, Section Botany, North-West University, Potchefstroom 2520, South Africa;3. Department of Biodiversity and Conservation Biology, University of the Western Cape, Private Bag X17, Bellville 7535, South Africa;4. Biozentrum Klein Flottbek & Botanischer Garten, University of Hamburg, Ohnhorststrasse 18, D-22609 Hamburg, Germany;1. Universidad Andrés Bello, Departamento Geología, Facultad de Ingeniería, Salvador Sanfuentes, 2357 Santiago, Chile;2. Servicio Geológico-Minero Argentino, Delegación Patagonia, Barrio Don Bosco km 8, Comodoro Rivadavia, Argentina;3. Servicio Nacional de Geología y Minería, Avenida Santa María, 0104 Santiago, Chile;4. Universidad Nacional de la Patagonia San Juan Bosco, Facultad de Ciencias Naturales, Dpto. de Geología, Km 4, Comodoro Rivadavia, Chubut, Argentina;5. Research School of Earth Sciences, The Australian National University, Canberra CT0200, Australia;1. Department of Plant Ecology and Environmental Conservation, Biological and Chemical Research Centre, Faculty of Biology, University of Warsaw, ul. ?wirki i Wigury 101, 02-089 Warsaw, Poland;2. Department of Botany, Kherson State University, ul. Universytetska 27, 73000 Kherson, Ukraine;1. Department of Earth Sciences, Uppsala University, Uppsala 752 36, Sweden;2. Australian Age of Dinosaurs Museum of Natural History, The Jump-Up, Winton, Queensland 4735, Australia;1. Environmental Sciences Department, University of Botswana, Private Bag 00704, Gaborone, Botswana;2. iThemba Laboratory for Accelerator Based Sciences, National Research Foundation, PO Box 722, 7129 Somerset West, South Africa;3. AGH University of Science and Technology, Faculty of Physics & Applied Computer Science, Al. A. Mickiewicza 30, 30-059 Krakow, Poland;4. Department of Chemistry, Rhodes University, PO Box 94, Grahamstown 6140, South Africa;1. State Key Laboratory of Advanced Processing and Reuse of Nonferrous Metals, Lanzhou University of Technology, Lanzhou, 730050, China;2. Key Laboratory of Nonferrous Metal Alloy and Processing, Ministry of Education, Lanzhou University of Technology, Lanzhou, 730050, China |
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| Abstract: | Current thermal regimes for many southern African succulent species of the subfamily Ruschioideae, which rapidly diversified during the cooler Pleistocene period, may be close to their tolerable extremes, and likely exceeded with anticipated future climate warming. This hypothesis was tested by exposing succulent species of different size and architecture to differently elevated temperatures approximating future African climate scenarios (2.5–3.8 °C increases in mean annual daily temperature maxima) using transparent hexagonal open-top chambers of different heights. Air temperatures, soil water potentials and amounts of fog and dew precipitation were monitored hourly in the differently heated open-top chambers and ambient environment, and changes in species leaf densities and canopy covers precisely determined in these chambers and ambient environment from high resolution digital images taken at 3-monthly intervals spanning a 12-month monitoring period. Photochemical efficiencies and activities of the photosynthetic enzyme Rubisco were also measured in one widespread dwarf succulent species following 2-h exposures of its populations in a forced draft oven to eight different heat intensities (range: 40–54 °C), the highest closely matching the temperature extreme of 54.8 °C recorded in the most intensively heated open-top chambers. After 12-months warming, all succulent species displayed massively (up to 90.2%) reduced leaf densities and canopy covers in the differently heated open-top chambers, with small sparsely branched species comprising single leaf pairs per axis exhibiting much greater reductions than large, shrubby or creeping species with multiple leaves. Noteworthy, was that fog and dew precipitation levels and soil water potentials at the centres of the least intensively heated chambers did not differ significantly from those in the ambient environment, even during the critical dry summer and early autumn seasons. However, leaf density and canopy reductions in these chambers were of similar magnitude to those in the most intensively heated chambers where fog and dew precipitation levels and soil water potentials were significantly reduced. These findings identified elevated temperatures as the principal cause of the observed massive reductions in leaf density and canopy cover and supported the hypothesis that mild anthropogenic warming could exceed the thermal thresholds of many southern African quartz field succulents leading to metabolic impairment. This impairment explained by an observed loss in the catalytic efficiency of Rubisco at daytime temperature extremes exceeding 54 °C, preceded by a decrease in PSII electron transport commencing at temperatures much lower than the threshold for Rubisco de-activation. |
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