The effect of elevated CO₂ on Phaseolus vulgaris L. cv Contender
- Authors: Mjwara, Jabulani Michael
- Date: 1997
- Subjects: Plants -- Effect of carbon dioxide on Kidney bean
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4215 , http://hdl.handle.net/10962/d1003784
- Description: 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.
- Full Text:
- Date Issued: 1997
- Authors: Mjwara, Jabulani Michael
- Date: 1997
- Subjects: Plants -- Effect of carbon dioxide on Kidney bean
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4215 , http://hdl.handle.net/10962/d1003784
- Description: 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.
- Full Text:
- Date Issued: 1997
The interactive effects of light, temperature and CO₂/O₂ ratios in photosynthesis of Coix lachryma-jobi L
- Authors: Mjwara, Jabulani Michael
- Date: 1992
- Subjects: Coix , Plants -- Effect of light on , Plants -- Effect of oxygen on , Plants -- Effect of carbon dioxide on , Photosynthesis , Plants -- Effect of temperature on
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4216 , http://hdl.handle.net/10962/d1003785
- Description: A portable infra red gas analyzer was used to investigate the interactive effects of light, temperature, and CO,jO, ratios under controlled environmental conditions in an attempt to model gas exchange characteristics of Coix Iachryma-jobi L. Plotting light response curves as a function of temperature (20, 25 30 and 35°C) revealed no sign of light saturation even at a photosynthetic photon flux density (PPFD) close to 2000 !Lmol m-' sol. High net assimilation rates (A) of approximately 24 !Lmol CO, m"s'! were realized at 30-35°C. Assimilation (A) versus internal CO, partial pressure (C,) curves showed a steep rise with increase in C, but saturated at approximately 150 (JLII-!) and all the results, either in the absence or presence of 0" showed a similar response under all temperature regimes. C. Iachryma-jobi exhibited low CO, compensation points cr ) between 0 and 10 JLlI-! under similar experimental temperatures and either at 0 or 21%0,. The slopes of double reciprocal plots of llA versus llCi, were nearly identical and crossed the yintercept at almost identical points under all 0, concentrations. These data indicate first; that there was no apparent 0, inhibition and second; indicated that the apparent inhIbitor constant (K,) for 0, at the site of carboxylation did not change with increase in [OJ from 0 to 21% oxygen. These observations were further confirmed by results obtained from the analysis of apparent carboxylation efficiency (CE, as defined as the slope of response of A to increasing CO,), as no inhibition of A with increase of [OJ occurred. These characteristics were consistent with typical features of C,photosynthesis. The absence of 0, inhibition and low r values indicated that an efficient CO, concentrating mechanism which eliminates photorespiration exists in C. Iachryma-jobi. At the light microscope level, leaf anatomy exhibited typical C, structure viz. bundle sheath with large chloroplasts and this sheath is further surrounded by a radiate Kranz mesophyU cells. Furthermore the anatomical features suggested that C. wchryma-jobi was an NADP-ME species. Stomatal conductance (g,) to assimilation (g,/A) indicated an increase in A with decrease in g" an essential feature of improving water use efficiency (WUE), but one which drastically reduces CO, diffusion rate. The physical lintitation (stomatal lintitation, t) to CO, diffusion under various [0,] and temperatures, but constant PPFD, did not exhibit statistically significant change in t values at either 0 or 21% a, within each temperature regime, however there was a marked decrease in t as the plant approached its optimum photosynthetic temperature.
- Full Text:
- Date Issued: 1992
- Authors: Mjwara, Jabulani Michael
- Date: 1992
- Subjects: Coix , Plants -- Effect of light on , Plants -- Effect of oxygen on , Plants -- Effect of carbon dioxide on , Photosynthesis , Plants -- Effect of temperature on
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4216 , http://hdl.handle.net/10962/d1003785
- Description: A portable infra red gas analyzer was used to investigate the interactive effects of light, temperature, and CO,jO, ratios under controlled environmental conditions in an attempt to model gas exchange characteristics of Coix Iachryma-jobi L. Plotting light response curves as a function of temperature (20, 25 30 and 35°C) revealed no sign of light saturation even at a photosynthetic photon flux density (PPFD) close to 2000 !Lmol m-' sol. High net assimilation rates (A) of approximately 24 !Lmol CO, m"s'! were realized at 30-35°C. Assimilation (A) versus internal CO, partial pressure (C,) curves showed a steep rise with increase in C, but saturated at approximately 150 (JLII-!) and all the results, either in the absence or presence of 0" showed a similar response under all temperature regimes. C. Iachryma-jobi exhibited low CO, compensation points cr ) between 0 and 10 JLlI-! under similar experimental temperatures and either at 0 or 21%0,. The slopes of double reciprocal plots of llA versus llCi, were nearly identical and crossed the yintercept at almost identical points under all 0, concentrations. These data indicate first; that there was no apparent 0, inhibition and second; indicated that the apparent inhIbitor constant (K,) for 0, at the site of carboxylation did not change with increase in [OJ from 0 to 21% oxygen. These observations were further confirmed by results obtained from the analysis of apparent carboxylation efficiency (CE, as defined as the slope of response of A to increasing CO,), as no inhibition of A with increase of [OJ occurred. These characteristics were consistent with typical features of C,photosynthesis. The absence of 0, inhibition and low r values indicated that an efficient CO, concentrating mechanism which eliminates photorespiration exists in C. Iachryma-jobi. At the light microscope level, leaf anatomy exhibited typical C, structure viz. bundle sheath with large chloroplasts and this sheath is further surrounded by a radiate Kranz mesophyU cells. Furthermore the anatomical features suggested that C. wchryma-jobi was an NADP-ME species. Stomatal conductance (g,) to assimilation (g,/A) indicated an increase in A with decrease in g" an essential feature of improving water use efficiency (WUE), but one which drastically reduces CO, diffusion rate. The physical lintitation (stomatal lintitation, t) to CO, diffusion under various [0,] and temperatures, but constant PPFD, did not exhibit statistically significant change in t values at either 0 or 21% a, within each temperature regime, however there was a marked decrease in t as the plant approached its optimum photosynthetic temperature.
- Full Text:
- Date Issued: 1992
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