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KMID : 0903519970400020134
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Journal of the Korean Society of Agricultural Chemistry and Biotechnology
1997 Volume.40 No. 2 p.134 ~ p.138
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Effect of Phosphorus Stress on Photosynthesis and Nitrogen Fixation of Soybean Plant under CO2 Enrichment
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Abstract
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The objective of this study was to examine the effect of phosphorus deficiency on nitrogen fixation and photosynthesis of nitrogen fixing soybean plant under CO₂ enrichment condition. The soybean plants(Glycine max [L.] Merr.) inoculated with Bradyrhizobium japonicum MN 110 were grown with P-stressed(0.05 mM-P) and control(1 mM-P) treatment under control(400 ㎕/L CO₂) and enrichment(800 ㎕/L CO₂) enviromental condition in the phytotron equipped with high density lamp(1000 μEm ^(-2)S^(-1)) and 28/22℃ temperature cycle for 35 days after transplanting(DAT). At 35 DAT, phosphorus deficiency decreased total dry mass by 64% in CO₂ enrichment condition, and 51% in control CO₂ condition. Total leaf area was reduced significantly by phosphorus deficiency in control and enriched COL condition but specific leaf weight was increased by P deficiency. Phosphorus deficiency significantly reduced photosynthetic rate(carbon exchange rate) and internal CO₂ concentration in leaf in both CO₂ treatments, but the degree of stress was more severe under CO₂ enrichment condition than under control CO₂ environmental condition. In phosphorus sufficient plants, CO₂ enrichment increased nodule fresh weight and total nitrogenase activity(acetylene reduction) of nodule by 30% and 41% respectively, but specific nitrogenase activity of nodule and nodule fresh weight was not affected by CO₂ enrichment in phosphorus deficient plant at 35 DAT. Total nitrogen concentrations in stem, root and nodule tissue were significantly higher in phosphorus sufficient plant grown under CO₂ enrichment, but nitrogen concentration in leaf was reduced by 30% under CO₂ enrichment. These results indicate that increasing CO₂ concentration does not affect plant growth under phosphorus deficient condition and phosphorus stress might inhibit carbohydrate utilization in whole plant and that CO₂ enrichment could not increase nodule formation and functioning under phosphorus deficient conditions and phosphorus has more important roles in nodule growth and functioning under CO₂ enrichment environments than under ambient condition.
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