Partitioning and Utilization of Apparent Photosynthate by Soybean (Glycine Max (L.) Merr.) Relative to Nitrogen Source: Nitrogen vs Nitrate
Finke, Robert Leslie
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https://hdl.handle.net/2142/77599
Description
Title
Partitioning and Utilization of Apparent Photosynthate by Soybean (Glycine Max (L.) Merr.) Relative to Nitrogen Source: Nitrogen vs Nitrate
Author(s)
Finke, Robert Leslie
Issue Date
1981
Department of Study
Plant Biology
Discipline
Plant Biology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Plant Physiology
Language
eng
Abstract
Nodulated and non-nodulated (not inoculated) soybeans (cv. Wells) were grown in controlled environments with N(,2) or non-limiting levels of NO(,3)('-) respectively serving as sole source of nitrogen. Plants were evaluated on the basis of whole plant efficiency of apparent photosynthate utilization relative to nitrogen assimilation (expressed as the ratio of moles of carbon respired by the whole plant to the moles of nitrogen incoporated into plant material). The efficiency of the N(,2)-fixing plants was compared with that of the nitrate-suplied plants on the basis of plant age and plant size.
Continuous 24 h CO(,2) exchange measurements on shoots and root systems made at the beginning of flowering (28 days after planting) indicated that N(,2)-fixing plants respired 8.28 moles of carbon per mole of dinitrogen-N fixed, while nitrate-supplied plants respired only 4.99 moles of carbon per mole of nitrate reduced. Twenty-one day old nitrate-supplied plants were even more efficient respiring only 3.18 moles of carbon per mole of nitrate reduced. On a size basis, the 28 day old N(,2)-fixing plants were intermediate between the 28 and 21 day old nitrate plants.
The calculated efficiencies were predominately a reflection of the root system respiration. N(,2)-fixing plants lost 25% of their daily net photosynthetic input of carbon through root system respiration, compared with 16% for 28 day old nitrate-supplied plants and 12% for 21 day old nitrate-supplied plants. The shoot dark respiration was similar for all three plant groups, varying between 7.9 and 9.0% of the apparent photosynthate.
The higher loss of carbon through respiration relative to nitrogen assimilation by the N(,2)-fixing plants was not compensated for by increased photosynthetic effectiveness. Canopy photosynthesis expressed on a leaf area basis was similar for 28 day old N(,2)-fixing plants (15.5 mg CO(,2) dm('-2)h('-1)) and 21 day old nitrate-supplied plants (14.5 mg CO(,2) dm('-2)h('-1)) which were similar in total canopy leaf area. The larger nitrate-supplied plants (28 day old) had lower photosynthetic rates (12.5 mg CO(,2) dm('-2)h('-1)), presumably due to self shading of the leaves.
These data indicate that during the early stages of plant development, dependency on N(,2)-fixation for the sole supply of required plant nitrogen is an expensive process compared to nitrate reduction in nitrate-supplied plants, since the N(,2)-fixing plants retained 8-12% less of their photosynthate as dry matter.
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