Abstract
An apparatus was designed that permitted acetylene reduction (N2 fixation) by root nodules to be measured in situ simultaneously with net photosynthesis, dark respiration, and transpiration of the shoot in soybean plants (Glycine max [L.] Merr. var. Beeson). Tests showed that acetylene reduction was linear with time for at least 5 hours, except for the first 30 to 60 minutes. Endogenous ethylene production did not affect the measurements. Successive determinations of acetylene reduction could be made without apparent aftereffects on the plant.
This apparatus was used to investigate the effects of soil flooding and desiccation on acetylene reduction under conditions where soil, nodule, and leaf water potentials could be measured. No acetylene reduction was detectable in flooded soil or in soil desiccated to a water potential of −19.5 bars. Between these extremes, acetylene reduction displayed a sharp optimum. Removing the soil eliminated the inhibitory effects of flooding, suggesting that rates of gas exchange were restricted between the nodules and the atnosphere at soil water potentials above −2 bars.
As the soil desiccated further, acetylene reduction decreased, and the decrease was correlated with decreases in photosynthesis and transpiration. Although dark respiration was inhibited, it was not affected to the extent that acetylene reduction, photosynthesis, or transpiration were. Consequently, it was concluded that photosynthesis, transpiration, or some direct effect on the nodules other than that caused by respiration were most likely to account for the inhibition of acetylene reduction at soil water potentials below −2 bars.
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Selected References
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- Boyer J. S., Bowen B. L. Inhibition of oxygen evolution in chloroplasts isolated from leaves with low water potentials. Plant Physiol. 1970 May;45(5):612–615. doi: 10.1104/pp.45.5.612. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Boyer J. S. Differing sensitivity of photosynthesis to low leaf water potentials in corn and soybean. Plant Physiol. 1970 Aug;46(2):236–239. doi: 10.1104/pp.46.2.236. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Boyer J. S. Isopiestic technique: measurement of accurate leaf water potentials. Science. 1966 Dec 16;154(3755):1459–1460. doi: 10.1126/science.154.3755.1459. [DOI] [PubMed] [Google Scholar]
- Boyer J. S. Leaf water potentials measured with a pressure chamber. Plant Physiol. 1967 Jan;42(1):133–137. doi: 10.1104/pp.42.1.133. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Burg S. P. Ethylene, plant senescence and abscission. Plant Physiol. 1968 Sep;43(9 Pt B):1503–1511. [PMC free article] [PubMed] [Google Scholar]
- Daesch G., Mortenson L. E. Effect of ammonia on the synthesis and function of the N 2 -fixing enzyme system in Clostridium pasteurianum. J Bacteriol. 1972 Apr;110(1):103–109. doi: 10.1128/jb.110.1.103-109.1972. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Hardy R. W., Holsten R. D., Jackson E. K., Burns R. C. The acetylene-ethylene assay for n(2) fixation: laboratory and field evaluation. Plant Physiol. 1968 Aug;43(8):1185–1207. doi: 10.1104/pp.43.8.1185. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Harper J. E. Canopy and Seasonal Profiles of Nitrate Reductase in Soybeans (Glycine max L. Merr.). Plant Physiol. 1972 Feb;49(2):146–154. doi: 10.1104/pp.49.2.146. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Jordan W. R., Morgan P. W., Davenport T. L. Water Stress Enhances Ethylene-mediated Leaf Abscission in Cotton. Plant Physiol. 1972 Dec;50(6):756–758. doi: 10.1104/pp.50.6.756. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Koch B., Evans H. J. Reduction of acetylene to ethylene by soybean root nodules. Plant Physiol. 1966 Dec;41(10):1748–1750. doi: 10.1104/pp.41.10.1748. [DOI] [PMC free article] [PubMed] [Google Scholar]
- LaRue T. A., Kurz W. G. Estimation of nitrogenase in intact legumes. Can J Microbiol. 1973 Feb;19(2):304–305. doi: 10.1139/m73-049. [DOI] [PubMed] [Google Scholar]