Submitted to: Journal of Plant Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 4, 2010
Publication Date: October 1, 2011
Citation: Sicher Jr, R.C. 2011. Photosynthetic acclimation and decreased chlorophyll (a & b) concentrations occur in nitrogen sufficient tobacco leaves in response to carbon dioxide enrichment. Journal of Plant Nutrition. 34:1995-2005. DOI: 10.1080/01904167.2011.610486.
Interpretive Summary: Carbon dioxide levels are rising in the atmosphere due to human activities. Plants grown in air containing elevated levels of carbon dioxide are usually bigger than the controls because carbon dioxide is needed for growth. However, over time some plants stop growing faster when in the presence of enhanced carbon dioxide because of chemical changes in the leaves. It is currently believed that changes in leaf chemistry can be prevented if very high levels of fertilizer are applied to the soil. We grew plants in air containing elevated carbon dioxide and with saturating amounts of fertilizer in the soil. Even with very high fertilizer levels some of the chemical changes due to increased carbon dioxide still took place in leaves. Therefore, high soil fertility alone cannot overcome all of the adjustments that take place in leaves in response to carbon dioxide enrichment and ultimately affect plant growth rates. Tobacco was used as a model plant in this investigation because it has very high nitrogen demands and its responses to carbon dioxide have been well studied. These results provide insights into carbon dioxide effects on the growth of soybean and wheat. These findings are of interest to environmentalists, nutritionists, plant physiologists, crop modelers, and to government policy makers.
The effects of CO2 enrichment on plant growth and on nitrogen partitioning were examined using fully-expanded tobacco leaves (Nicotiana tabacum L. cv. Samsun). Plants were grown from single seeds in matching controlled environment chambers with continuous ambient CO2 partial pressures of 38 to 40 Pa. After 5 weeks growth one-half of the plants were transferred to a second chamber providing 68 to 70 Pa CO2 for 8 days. Total above ground dry matter, total leaf area, and specific leaf weight were unchanged (P > 0.05) by CO2 enrichment. Total soluble protein, total soluble amino acids, and inorganic nitrate also were unaffected by CO2 enrichment (P > 0.05), thereby showing that the tobacco plants in this study were nitrogen sufficient. Leaf chlorophyll (a + b) levels were decreased 13% (P < 0.05) in response to CO2 enrichment, but this was attributed to yellowing that was independent of nitrogen status. Also, the diurnal accumulation of soluble amino acids in tobacco leaves was delayed and the initial slope of the A/Ci response curve was decreased 14% in the elevated compared to the ambient CO2 treatment. The above findings showed that CO2 enrichment affected leaf chlorophyll levels, diurnal soluble amino acid metabolism and photosynthetic responses to low intercellular CO2 concentrations, even though the plants were nitrogen sufficient. Therefore, inadequate nitrogen fertility can not explain all of the effects of CO2 enrichment on carbon assimilation by tobacco leaves.