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Accueil du site → Doctorat → Afrique du Sud → 2001 → The effect of elevated CO2 levels on the growth of two Acacia species.

University of KwaZulu-Natal (2001)

The effect of elevated CO2 levels on the growth of two Acacia species.

Lotz, Michelle Karen.

Titre : The effect of elevated CO2 levels on the growth of two Acacia species.

Auteur : Lotz, Michelle Karen.

Université de soutenance : University of KwaZulu-Natal

Grade : Master of Science (MS) 2001

Climate change, induced by increases in the concentration of greenhouse gases in the atmosphere, can affect the growth and community structure of ecosystems in two ways. Firstly directly through changes in atmospheric concentration of CO2, and secondly indirectly through changes in temperature and rainfall. The aim of the present investigation was to test the effect of elevated CO2 and altitude-related temperature differences on the growth of two species of Acacia that form important components of the vegetation of KwaZulu-Natal. Plants of Acacia sieberana and Acacia nilotica were grown in chambers at elevated (700 pll-1) and ambient (350 IJW1) CO2 with and without rhizobial inoculation. Both treatments (elevated CO2 and the presence of rhizobial inoculation) stimulated growth and branching. A. nilotica was the most responsive to both elevated CO2 level and inoculation. Inoculated plants showed greater increases in mass and height than uninoculated plants. While elevated CO2 had a significant effect on plant mass, height and leaf area accumulation, other factors, such as species type and rhizobial inoculation had a somewhat greater influence on the short term mass accumulation under elevated CO2 , Significant differences existed between the average percentage leaf nitrogen for the two species (P < 0.001), and for inoculated and uninoculated plants (P < 0.005). There were no significant differences in photosynthetic rates (A) at any internal CO2 concentration (Cj) between plants grown in elevated CO2 compared to those grown under ambient conditions. When photosynthesis was plotted against C, (A/CJ, the initial slopes of the graphs for both A. sieberana and A. nilotica were shallower for plants grown in elevated CO2 , compared to plants grown in ambient conditions , indicating a decreased Rubisco concentration at low C, and greater nitrogen use efficiency. At higher C ; A. sieberana continued to have lower A in plants grown at elevated CO2 levels suggesting an inability to regenerate RuBP or the possible accumulation of soluble carbohydrates.


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