Submitted to: Photosynthesis Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 28, 2001
Publication Date: N/A
Interpretive Summary: Atmospheric carbon dioxide will double during the next century due to the rapid pace of industrialization and deforestation. This could impact agricultural sustainability because plant growth is accelerated by enhanced carbon dioxide. Larger and faster growing plants create an increased demand for soil nutrients, particularly nitrogen. Plant growth with enriched carbon dioxide can be limited by rates of nitrogen uptake and utilization. Moreover, wheat and rice plants grown with elevated carbon dioxide often have a decreased percentage of total reduced nitrogen in the foliage and in the grain. The possibility, that losses of chlorophyll and leaf protein in carbon dioxide enriched plants were due to a growth induced nitrogen limitation, was tested. Nitrate and ammonium in barley leaves were measured at ambient and three times ambient carbon dioxide in the present controlled environment study using a complete mineral nutrient solution. Enzyme activity and amino acids involved in nitrate and ammonium assimilation were also determined. Elevated carbon dioxide produced small but significant changes in the nitrogen metabolism of barley leaves. It was concluded that low chlorophyll levels with enhanced carbon dioxide were not attributable to a growth induced nitrogen limitation. These findings supported the suggestion that future agricultural systems will be dependent on high soil fertility to avoid nitrogen limiting growth conditions and to protect the nutritional value of foods. Agricultural scientists, crop modelers, and government policy makers who have interest in Global Climate Change will benefit from this research.
Technical Abstract: Effects of atmospheric carbon dioxide enrichment on nitrogen metabolism and nitrate reductase activity were studied in barley primary leaves (Hordeum vulgare L. cv. Brant). Plants were grown in chambers under ambient (36 Pa) and elevated (100 Pa) carbon dioxide were fertilized daily with complete nutrient solution providing 12 millimolar nitrate and 2.5 millimolar ammonium. Foliar nitrate and ammonium were 27% and 42% lower (P greater than 0.01) in the elevated compared to ambient carbon dioxide treatments, respectively. A diurnal variation of ammonium was absent in the elevated carbon dioxide treatment. Enhanced carbon dioxide affected leaf ammonium levels by inhibiting photo respiration. Foliar nitrate was greater than 50 to 100-fold ammonium and variations of total nitrate were not observed in either treatment. Total and Mg2+ inhibited nitrate reductase activities were slightly lower (P greater than 0.01) in enhanced compared to ambient carbon dioxide between eight and 15 DAS. The diurnal variation of total nitrate reductase activity in barley primary leaves was similar in ambient and elevated carbon dioxide but enzyme measurements taken between seven and 10 h of the photo period were decreased (P greater than 0.05) by carbon dioxide enrichment. The above findings showed only slight modifications in leaf nitrogen metabolisms. Consequently, it was not likely that the extensive chlorosis of barley primary leaves observed under enhanced carbon dioxide was attributable to a nutritionally induced nitrogen limitation.