No description available.

The atmospheric (CO2) partial pressure is expected to continue to increase and the scenario is that the CO2 partial pressure will reach 50-70 Pa during the 21st century.The rise in CO2 will have a direct influence on plant growth and development because CO2 is the primary substrate for photosynthesis.The aim of the studies described in this thesis was to investigate the response of grasses belonging to two subtypes to a range of CO2 partial pressures under conditions where light intensity, water and N supplies were varied.Two species which are naturalized in Australia, Panicum coloratum (NAD-ME) and Cenchrus ciliaris (NADP-ME) were chosen for a series of experiments conducted in matched growth chambers. The response of C4 plants is particularly important for Australia because they dominate the tropical grasslands that occupy 75% of the continent and form the basis for the pasture industry. Following the extensive research conducted in this study, it can be concluded that the inevitable rise in atmospheric CO2 partial pressure will increase the growth of C4 grasses when other resources are not limiting.Growth of C4 grasses will be stimulated to a greater extent under conditions of drought. / Doctor of Philsophy (PhD)

Thesis (Ph. D.)--University of California, Davis and San Diego State University, 2003. / Includes bibliographical references (leaves 95-101). Also available via the World Wide Web. (Restricted to UC campuses).

No description available.

Subsurface peat decomposition, through CO2 production, was analyzed in laboratory and field experiments in a bog, poor fen, and beaver pond margin at Mer Bleue, Ottawa. Intact core samples in 10 cm depth intervals from 5--45 cm below the surface of each site were incubated in the laboratory. Treatments involved aerobic and anaerobic conditions at 4 and 14°C. Field measurements of CO2 flux were made by a static chamber technique. / Incubation results indicate modelled CO2 surface fluxes differ amongst wetlands. Aerobic CO2 modelled surface fluxes at 4°C were 2.3, 3.1 and 4.2 g CO2 m-2 d-1 for the bog, the beaver pond margin, and the poor fen, respectively. On average, aerobic production rates from peat cores with field moisture conditions were 11.7 times larger than anaerobic production rates. A mean Q10 of 2.3 defined the role of temperature. Differences among the peat samples were related to degree of decomposition, and differences among the sites were related to trophic status and nutrient availability. / A model of CO2 production was constructed and validated against field fluxes of CO2. The model provides a good prediction (r 2 = 0.72) of subsurface peat decomposition. The results suggest that warmer peat temperatures and lowered water tables, as predicted by climate change scenarios, will increase surface CO2 fluxes due to peat decomposition.

Rising atmospheric CO2 (Ca) concentrations have generated concern among scientists, mainly because of CO2’s role as a greenhouse gas and its influence on plant growth and development. Previous research has suggested that future CO2 enriched atmospheres may enhance the success of invasive aliens. Chromolaena odorata is an example of an invasive alien proving to be a serious threat to indigenous vegetation in South Africa, and effective control measures are desperately needed to curb infestations in the future. The current study aimed at assessing the response of C. odorata to elevated Ca and interactive factors, and was divided into two trials. During PART A, C. odorata was grown in competition with 2 grass species: Eragrostis curvula and Themeda triandra (selected for their differential preferences to nutrient availability). All three species were potted in a greenhouse at the University of KwaZulu-Natal (Howard College). There were 16 pots in total, and each pot contained four C. odorata plants, four T. triandra seedlings, and four E. curvula seedlings. Eight pots were exposed to elevated Ca (~700ppm), and eight pots were exposed to ambient Ca (~370ppm). The pots at each Ca treatment were further divided: four received high nutrient treatments (3L per addition), while the other four received low nutrient treatments (300 ml per addition). Studies on growth (e.g. plant height, dry weight, etc.), as well as physiology (e.g. Jmax), were undertaken. Results showed that generally, plants responded positively to high nutrient treatments. In contrast, elevated Ca did not affect growth or any of photosynthetic parameters of C. odorata significantly, but did reduce stomatal limitations. During PART B, C. odorata plants were grown monospecifically to assess whether there was a “chamber effect” associated with planting density. Pots at both Ca treatments contained either four C. odorata or two C. odorata seedlings. Growth and physiology were assessed. The fact that elevated Ca did not affect any of the photosynthetic parameters studied, suggests that photosynthetic down-regulation did not occur. This, together with the fact that no increase in stomatal limitations were observed in elevated Ca, implies that enhancement of photosynthetic assimilation could have occurred in C. odorata plants exposed to CO2 enrichment. Results from this study (PART A and PART B), when compared to previous research on this species, suggests that CO2 enrichment may enhance the success of monoculture populations of C. odorata. However, other species may gain competitive advantages over C. odorata occurring in mixed communites, under CO2 enriched environments. In addition, results of this study support the prediction that increasing Ca will reduce the importance of carbon as an external limiting resource, and that the extent of a plant’s response to Ca enrichment will depend on resources other than CO2. If increases in temperature caused by elevated Ca increases nutrient availability in the soil, then Ca could indirectly enhance the success of C. odorata occurring in mixed communities. / Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2008.

Daily net ecosystem CO$ sb2$ exchange (NEE) was monitored at several peatland communities in a mid-boreal headwater bog at the Experimental Lakes Area (Kenora, ON., Canada) throughout the 1995-96 growing seasons. Transparent and opaque chamber systems were used to measure NEE and dark respiration at replicate plots in which the vascular vegetation was either clipped or unclipped. CO$ sb2$ fixation and emission fluxes were estimated from NEE measurements and were compared within and among the peatland communities. Communities that supported shrubby, xerophytic vegetation fixed CO$ sb2$ at rates that ranged from, on average, 0.194 to 0.365 mg CO$ sb2$ m$ sp{-2}$ s$ sp{-1}$. These rates did not vary significantly on a daily to weekly timescale, and were comparable in magnitude to the wetter, sedge-dominated communities. CO$ sb2$ emissions varied within and among communities across the sampling season. Rates were, on average, from 0.0568 to 0.109 mg CO$ sb2$ m$ sp{-2}$ s$ sp{-1}$, and the variation was associated with differences in ground temperature and water table. Comparisons of CO$ sb2$ emissions from clipped and unclipped plots allowed an estimation of the contribution of vascular respiration to total CO$ sb2$ emissions. Contributions ranged from 25 to over 80%, depending on the community and season that the measurements were taken. Strong associations between vascular respiration and ground temperature were observed. Daily NEE had little variability between communities and throughout the sampling season. This was attributed to parallel variations for the CO$ sb2$ fixation and emission fluxes. Researchers should quantify the actual fluxes for vascular root respiration, as it possibly controlled a large part of the NEE variability within and between sites.

It is generally accepted that global levels of CO2 will roughly double over the next century. Because of their large population sizes and fast generation times, microalgae may adapt to global change through novel mutations fixed by natural selection, such that future populations may be genetically different from contemporary ones. The prediction that microalgae may respond evolutionarily to rising CO2 was tested using populations of Chlamydomonas reinhardtii grown for 1000 generations at increasing CO2. Laboratory populations grown at high CO2 did not show a direct response to selection at elevated CO2, instead evolving a range of non-adaptive syndromes. In addition, populations selected at elevated CO2 often grew poorly at ambient CO2. The same evolutionary responses were seen in natural populations isolated from CO2 springs. CO2 uptake was measured in a subset of the laboratory selection lines, which were found to have cells that either leaked CO2, had lost the ability to induce high-affinity CO 2 uptake, or both. These phenotypes were tentatively attributed to the accumulation of conditionally neutral mutations in genes involved in the carbon concentrating mechanism (CCM). The high-CO2-selected phenotypes were found to be reversible in terms of fitness when populations were backselected in air, though wild-type regulation of the CCM was not regained. It has been suggested that phytoplankton adaptation to changes in CO2 levels is constrained by selective history. This was tested by culturing genetically distinct populations of Chlamydomonas at decreasing levels of CO2. In this case, divergence between lines was attributable to chance rather than selective history.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaves 60-64). Also available via the Internet.

Thesis (MSc) -- Macquarie University, Division of Environmental and Life Sciences, Dept. of Chemistry and Biomolecular Sciences, 2008. / Bibliography: p. 120-124.