This investigation was initiated to study the effect of CO₂ on phytochrome-mediated morphogenesis in flowering and seed germination. Removal of CO₂ by flushing the plant environment with CO₂-free air inhibited the red light interruption effects on flowering in Xanthium pennsylvanicum and on seed germination in Lactuca sativa cv Grand Rapids. Further experiments were done to investigate the involvement of CO₂ exchange in the effects of night interruptions on flowering in Xanthium. ¹⁴CO₂ feeding trials showed that red light given for 5 minutes caused a net increase in ¹⁴C activity in the ethanol soluble fraction when ¹⁴CO₂ was fed during the light treatment. There was no effect of red light on the extent of ¹⁴CO₂ fixation in the dark period immediately following red light. The types of free amino acids recovered after paper chromatography were essentially the same after ¹⁴CO₂ feedings in darkness, red light, and far red light following red light. However, there was a considerable increase in ¹⁴C activity in most of the amino acids in leaves given red light interruption, and the amount further increased when far red light was given following the red light. The extent of ¹⁴C label in tyrosine, valine and leucine was essentially the same in all the three treatments. In CO₂-exchange experiments using the IRGA, brief red or far red light treatments were applied to Xanthium plants under inductive dark periods and the subsequent flowering response was assessed according to bud morphology. The occurrence of flowering depended on the timing, wavelength and intensity of the light treatments, and on the CCL concentration during the light treatments. CO₂ exchange was measured during the night interruptions in single attached leaves. CO₂ exchange was influenced by the conditions during the night interruptions, but there was no apparent correlation between the pattern of CO₂ exchange observed and the subsequent flowering response. It appears that the action of during night interruptions is not associated with the exchange of during the night interruption. In an attempt to investigate other possible roles of CO₂, experiments were done with light sensitive lettuce and Amaranthus retroflexus L. seeds. These experiments pertained to changes in pH of the incubation medium and CO₂ concentration simultaneously. Germination was strongly promoted at pH 4.0 but the promotion diminished with increases in pH and did not occur at pH 7.5. The response of germination to red irradiation was suppressed by CO₂ removal and enhanced by CO₂ enrichment in air or atmospheres. There was a close similarity between the pH effects on percentage germination and pH dependence of the CO₂ /HCO₃ - equilibrium. Transfer experiments, in which lettuce seeds were exchanged between buffers of pH 4.0 and pH 3.0, showed that the red/far red photo-transformation of phytochrome v/as independent of pH. Low pH, however, was required for onset of germination following red irradiation. Thereafter, pH between 4.0 and 8.0 did not limit the progress of germination. It is postulated that following red irradiation, a product develops which is distinguishable from the Pfr form of phytochrome. The product is stable at pH 8.0 and at pH 4.0 it acts to promote germination. / Science, Faculty of / Botany, Department of / Graduate

by Wing-kin Yip. / Bibliography: leaves 79-83 / Thesis (M.Phil.) -- Chinese University of Hong Kong, 1983

Typescript (photocopy) / x, 210 leaves, [2] leaves of col. plates : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Botany, 1982

The response of Phaseolus vulgaris L. cv. Contender grown in controlled environmental conditions, at either ambient or elevated (360 and 700 μmol mol ̄¹, respectively) CO₂ concentrations ([CO₂]), was monitored from 10 days after germination (DAG) until the onset of senescence. Elevated CO₂ had a pronounced effect on total plant height (TPH), leaf area (LA), dry weight (DW) accumulation and specific leaf area (SLA). All of these were significantly increased by elevated [CO₂] with the exception of SLA, which was significantly reduced. Except for higher initial relative growth rates (RGR) in CO₂-enriched plants, RGR did not differ significantly between the two CO₂ treatments throughout the remainder of growth period. While growth parameters clearly differed between CO₂ treatments, the effects of CO₂ on many physiological processes including net assimilation rate (NAR), Rubisco activity, and some foliar nutrient concentrations were largely transient. For example, CO₂ enrichment significantly increased NAR, but from 20 DAG onward, NAR declined to levels measured on plants grown under ambient CO₂. Similarly, the decline in both foliar N concentration and Rubisco activity in CO₂-enriched plants after 20 DAG was significantly greater than the decline observed for ambient CO₂ plants. Soluble leaf protein and total chlorophylls (a+b) were also significantly reduced in plants grown under elevated CO₂. Chlorophyll (a/b) ratios increased with time underelevated CO₂, indicating that the rate of decline of chlorophyll b was higher than that of chorophyll α. No significant changes in total carotenoid (x+c) levels were observed in either CO₂ treatment. Under enhanced CO₂, the foliar concentrations of K and Mn were increased significantly, while P, Ca, Fe and Zn were reduced significantly. However, changes in Mg and Cu concentrations were not significant. High CO₂-grown plants also exhibited pronounced leaf discoloration or chlorosis, coupled with a significant reduction in leaf longevity. The levels of non-structural carbohydrates (sucrose, glucose, fructose and starch) and nitrogenous compounds (nitrogen, total soluble proteins and free amino acids) were determined for leaves and developing seeds of P. vulgaris. Leaf tissue of elevated CO₂-grown plants accumulated significantly higher levels of both soluble sugars and starch. Leaf ultrastructure revealed considerable erilargement of starch grain sizes with surface areas more than five times larger compared to those of control plants. No apparent differences in structure and membrane integrity of chloroplasts in both CO₂ treatments were noted. Although ambient CO₂-grown plants had comparatively low levels of non-structural carbohydrates (NSC), they accumulated significantly higher levels of nitrogenous compounds. The levels of NSC were consistently higher in seeds of plants grown under elevated CO₂. In comparison to plants grown at elevated [CO₂], pods and seeds of ambient CO₂-grown plants had significantly larger pools of free amino compounds and N. Stomatal conductance (gs) declined significantly, as expected for plants grown under elevated CO₂. This was accompanied by a decline in transpiration rates (E). Reduced gs and E led to high AlE ratio, which meant improved water use efficiency (WUE) values for CO₂-enriched bean plants. Leaf carbon isotope discrimination (∆) against the heavier isotope of carbon (¹³C), has been used to select for high WUE in C₃ plants. In plants grown at elevated CO₂ concentration, ,1 was significantly reduced. Although ∆ was negatively correlated with WUE in both CO₂ treatments, the correlation was steeper and highly negative for CO₂-enriched plants. These results indicate underlying differences in gas-exchange physiology, including stomatal responses between ambient and elevated CO₂-grown plants. Photosynthetic acclimation was investigated using the response of assimilation to internal carbon dioxide concentration (A/C₁ curves). At early stages of growth, the initial slope of the A/C₁ response curve did not differ with CO₂ treatment. In contrast, CO₂-saturated photosynthetic rate (Amax) was significantly higher in plants grown under elevated versus ambient CO₂ at 15 DAG. However, at subsequent stages of growth both the initial slope and Amax declined in bean plants grown in elevated CO₂. Apparent carboxylation efficiency (ACE, estimated from the initial slope of A/C₁ response) values followed a similar trend and were significantly reduced in CO₂-enriched plants. These results indicate that acclimation or negative adjustment of photosynthesis may have been caused by a combination of both stomatal and biochemical limitations. Bean plants grown under conditions of elevated atmospheric CO₂ flowered 3 to 4 days earlier, and produced significantly more flowers and pods than plants grown at ambient conditions. Plants grown at elevated CO₂ aborted 22 and 20% more flowers and pods, respectively, than plants grown at ambient CO₂. Elevated CO₂ also significantly increased the number of tillers or lateral branches produced by plants, which contributed to a significant increase in pod number and seed yield in these plants. Although plants grown at elevated CO₂ produced on average 8 seeds per pod, while plants grown under ambient CO2 conditions produced 5 seeds per pod, the greater number of seeds was offset by lower seed weights in plants grown under _ elevated CO₂. Thus, despite high seed yield in beans grown under elevated CO₂, the harvest index (HI) did not change significantly between CO₂ treatments.

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg in fulfilment of the requirements for the degree of Master of Science. Johannesburg 1995 / This project represents the development of a comprehensive description of the growth of two plant species (namely white clover and Italian ryegrass) in a mixed canopy: Particular attention has been paid to the impact of two symbiotic associations (legume root nodules and vesicular arbuscular mycorrhizae) on the growth of the two plant species. [Abbreviated Abstract. Open document to view full version] / MT2017

Seasonal and inter-annual variation in carbon dioxide exchange and carbon balance in a mixed grassland by Peter Carlson Chairperson of the Supervisory Committee: Professor Lawrence Flanagan Department of Biological Science Eddy covariance measurements were carried out to document the seasonal and inter-annual variation in CO2 flux in a mixed prairie grassland. There was very different net ecosystem carbon exchange between the two years of study. In 1998 the maximum net ecosystem carbon exchange was 4.95 g C m-2d-1, compared to 2.50 g C m-2d-1 in 1999. The most important environment control on CO2 uptake was volumetric soil moisture content through its affect on leaf area index. There was evidence of stomatal limitation of CO2 uptake, during periods of atmospheric drought. The total seasonal net ecosystem carbon gain for 1998 was 190.0 g C m-2, compared with 46.8 g C m-2 in 1999. This grassland is a large carbon sink in a growing season of above normal precipitation. In a year of normal summer precipitation, this grassland is a small carbon sink, replacing slightly more carbon than is lost through winter respiration. / xi, 99 leaves : ill. ; 28 cm.

The enormous burning of fossil fuel and deforestation have caused an increase in the atmospheric CO₂ concentration ([CO₂]) during the last century. This will invariably have profound direct and indirect effects on plant carbon metabolism. The majority of research on the effects of CO₂ enrichment on plants are short-term and are done on other crops, but very little have been done on barley. This project aimed to determine the effects of long-term CO₂ enrichment on photosynthesis, growth and grain yield on barley. Hordeum vulgare L. cvs Stirling and Schooner plants were grown from seeds in controlled environment chambers at ambient (350) and elevated (600) μmol molˉ¹ [CO₂]. Measurements of net assimilation rate (NAR), photosynthetic pigments content and growth parameters were started 7 days after germination (DAG) and continued until senescence. The anatomy of matured fully developed leaves was also monitored. Elevated [CO₂l resulted in an increase in NAR in the two cultivars from days 7 until 14, after which the stimulation of NAR of CO₂-enriched plants started to decrease. At the onset of senescence, NAR was almost equal in plants grown under both ambient and elevated [CO₂]. The response of assimilation as a function of internal [CO₂l (C₁) at the end of the experimental period showed a significant decrease in both the initial slope of the A/C₁ curves and the CO₂-saturated photosynthetic rates in the two cultivars. Stirling showed no significant changes in the content of chlorophyll α,chlorophyll б or in total carotenoids. However, Schooner showed a stimulation in chlorophyll α content at day 7, but decreased at day 28. Chlorophyll б and total carotenoids content were not affected by CO₂ enrichment. While total above-ground biomass was not affected by elevated [CO₂] in the two cultivars, total plant height decreased significantly after 14 days in Stirling whereas no significant change occurred in Schooner throughout the experimental period. Leaf area was not significantly affected by CO₂ enrichment in the two cultivars although the leaves in CO₂ enriched plants were slightly shorter. Anatomical studies reveal that leaf thickness was significantly increased by CO₂ enrichment in Stirling, but the increase was not significant in Schooner. Both cultivars did not show any significant effect on chloroplast morphology and ultrastructure as a consequence of elevated CO₂ exposure. No signs of starch accumulation were evident in variety Schooner, but Stirling showed some form of starch accumulation, under increased atmospheric [CO₂]. Elevated CO₂ resulted in a significant reduction by more than 50 % in the number of grain yield per plant in both Stirling and Schooner. Results from this study therefore indicate that CO₂ enrichment will not be beneficial in terms of growth and yield in this important crop.

Call number: LD2668 .T4 1986 C87 / Master of Science / Chemical Engineering

Thesis (MSc)--Stellenbosch University, 2000. / ENGLISH ABSTRACT: This investigation was undertaken to determine whether elevated concentrations of dissolved inorganic carbon (DIC) supplied to plant roots could improve plant growth and alleviate the effects of salinity stress on tomato plants infected with arbuscular mycorrhizae. Lycopersicon esculentum cv. FI44 seedlings were grown in hydroponic culture (pH 5.8) with 0 and 75 mM NaCI and with or without infection with the fungus Glomus mosseae. The root solution was aerated with ambient CO2 (360 ppm) or elevated CO2 ( 5 000 ppm) concentrations. The arbuscular and hypha I components of mycorrhizal infection as well as the percentages total infection were decreased or increased according to the variation in seasons. The plant dry weight of mycorrhizal plants was increased by 30% compared to non-mycorrhizal plants at elevated concentrations of CO2, while the dry weight was decreased by 68% at ambient CO2 concentrations. Elevated CO2 also stimulated the growth of the mycorrhizal fungus. Elevated CO2 increased the plant dry weight and stimulated fungal growth of mycorrhizal plants possibly by the provision of carbon due to the incorporation of HCO)- by PEPc. Plant roots supplied with elevated concentrations of CO2 had a decreased CO2 release rate compared to roots at ambient CO2. This decrease in CO2 release rate at elevated CO2 was due to the increased incorporation of HC03- by PEPc activity. Under conditions of salinity stress plants had a higher ratio of N03-: reduced N in the xylem sap compared to plants supplied with 0 mM NaCI. Under salinity stress conditions, more N03- was transported in the xylem stream possibly because of the production of more organic acids instead of amino acids due to low P conditions under which the plants were grown. The N03· uptake rate of plants increased at elevated concentrations of CO2 in the absence of salinity because the HCO)- could be used for the production of amino acids. In the presence of salinity, carbon was possibly used for the production of organic acids that diverted carbon away from the synthesis of amino acids. It was concluded that mycorrhizas were beneficial for plant growth under conditions of salinity stress provided that there was an additional source of carbon. Arbuscular mycorrhizal infection did not improve the nutrient uptake of hydroponically grown plants. / AFRIKAANSE OPSOMMING: In hierdie studie was die effek van verhoogde konsentrasies opgeloste anorganiese koolstof wat aan plant wortels verskaf is, getoets om te bepaal of dit die groei van plante kan verbeter asook of sout stres verlig kon word in tamatie plante wat met arbuskulêre mikorrhizas geïnfekteer was. Lycorpersicon esculentum cv. FJ44 saailinge was in water kultuur gegroei (pH 5.8) met 0 en 75 mM NaCI asook met of sonder infeksie met die fungus Glomus mosseae. Die plant wortels was bespuit met normale CO2 (360 dele per miljoen (dpm)) sowel as verhoogde CO2 (5 000 dpm) konsentrasies. Die arbuskulere en hife komponente, sowel as die persentasie infeksie was vermeerder of verminder na gelang van die verandering in seisoen. Die plant droë massa van mikorrhiza geïnfekteerde plante by verhoogde CO2 konsentrasies was verhoog met 30% in vergelyking met plante wat nie geïnfekteer was nie, terwyl die droë massa met 68% afgeneem het by gewone CO2 konsentrasies. Verhoogde CO2 konsentrasies het moontlik die plant droë massa en die groei van die fungus verbeter deur koolstof te verskaf as gevolg van die vaslegging van HCO)- deur die werking van PEP karboksilase. Plant wortels wat met verhoogde CO2 konsentrasies bespuit was, het 'n verlaagde CO2 vrystelling getoon in vergelyking met die wortels by normale CO2 vlakke. Die vermindering in CO2 vrystelling van wortels by verhoogde CO2 was die gevolg van die vaslegging van HC03- deur PEPk aktiwiteit. Onder toestande van sout stres, het plante 'n groter hoeveelheid N03- gereduseerde N in die xileemsap bevat in vergelyking met plante wat onder geen sout stres was nie, asook meer NO)- was in die xileemsap vervoer moontlik omdat meer organiese sure geproduseer was ten koste van amino sure. Dit was die moontlike gevolg omdat die plante onder lae P toestande gegroei het. Die tempo van NO.; opname was verhoog onder verhoogde CO2 konsentrasies en in die afwesigheid van sout stres omdat die HCO)- vir die produksie van amino sure gebruik was. In die teenwoordigheid van sout was koolstof moontlik gebruik om organiese sure te vervaardig wat koolstof weggeneem het van die vervaardiging van amino sure. Daar is tot die slotsom gekom dat mikorrhizas voordelig is vir die groei van plante onder toestande van sout stres mits daar 'n addisionele bron van koolstof teenwoordig is. Arbuskulere mikorrhiza infeksie het 'n geringe invloed gehad op die opname van voedingstowwe van plante wat in waterkultuur gegroei was.

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