To study the role or organic substrate availability as a factor limiting associative N2-fixation we measured acetylene reduction (AR) associated with roots of intact maize and sorghum plants before and after adding organic substrates to the nutrient solution in a hydroponic system. Chloramphenicol (Cam) or nalidixic acid (NA) was added along with the substrate to determine whether bacterial protein synthesis or cell replication was necessary to support increased AR following amendment. The grasses were grown in pots in a greenhouse or on a light bench for 4–6 weeks, and then brought into the laboratory to measure AR. Intact plants were separated from soil and transferred into plastic cylinders containing an N-free nutrient solution. The roots were isolated from the shoots by a silicone rubber seal and exposed to oxygen concentrations of 0–10 kPa. Rates of AR were measured before and after adding 0.01–0.10% (w/v) carbon as glucose, malate, succinate, ethanol, acetate, glutarate, propionate, or resorcinol. Only resorcinol and ethanol failed to substantially increase AR activity. Rates of AR increased by 1.5-to 2-fold within 2h and by 5-to 15-fold after 24h. Cam and NA prevented the stimulation of AR by glucose, but neither inhibitor caused AR associated with unamended plants to decrease. We conclude that the highly variable rates of AR that have been reported for associative symbioses, even under well-controlled conditions were governed to a large extent by the amount and type of organic substrates exuded by the roots. Proliferation of diazotrophs appeared to be necessary to increase root-associated AR activity but not to maintain a constant level of activity.
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Alexander D B and Zuberer D A 1988 Impact of soil environmental factors on rates of N2 fixation associated with roots of intact maize and sorghum plants. Plant and Soil (In press)
Alexander D B, Zuberer D A and Vietor D M 1987 Nitrogen fixation (C2H2 reduction) associated with roots of intactZea mays in fritted clay at reduced oxygen tensions. Soil Biol. Biochem. 19. 1–6.
Baker D and Huss-Danell K 1986 Effects of oxygen and chloramphenicol onFrankia nitrogenase activity. Arch. Microbiol. 144, 233–236.
Bowen G D 1980 Misconceptions, concepts, and approaches in rhizosphere biology.In Contemporary Microbial Ecology. Eds. D C Elwood et al. pp 107–150. Academic Press, London.
Brouzes R, Mayfield C I and Knowles R 1971 Effect of oxygen partial pressure on nitrogen fixation and acetylene reduction in a sandy loam soil amended with glucose. Plant and Soil, Special Vol., 481–494.
Burris R H 1977 A synthesis paper on nonleguminous N2-fixing systems.In Recent Developments in Nitrogen Fixation. Eds. W Newton et al. pp 487–511. Academic Press, London.
De-Polli H, Matsui E, Döbereiner J and Salati E 1977 Confirmation of nitrogen fixation in two tropical grasses by15N2 incorporation. Soil Biol. Biochem. 9, 119–123.
Döbereiner J 1977 Physiological aspects of N2 fixation in grassbacteria associations.In Recent Developments in Nitrogen Fixation. Eds. W Newton et al. pp 513–522. Academic Press, London.
Döbereiner J, Marriel I E and Nery M 1976 Ecological distribution ofSpirillum lipoferum Beijerinck. Can. J. Microbiol. 22, 1464–1473.
Gaskins M H, Albrecht S L and Hubbell D H 1984/85 Rhizosphere bacteria and their use to increase plant productivity: A review. Agric. Ecosys. Environ. 12, 99–116.
Haahtela K, Kari K and Sundman V 1983 Nitrogenase activity (acetylene reduction) of root-associated, cold-climateAzospirillum, Enterobacter, Klebsiella, andPseudomonas species during growth on various carbon sources and at various partial pressures of oxygen. Appl. Environ. Microbiol. 45, 563–570.
Haahtela K, Wartiovaara T, Sundman V and Skujins J 1981 Root-associated N2 fixation (acetylene reduction) byEnterobacteriaceae andAzospirillum strains in cold-climate spodosols. Appl. Environ. Microbiol. 41, 203–206.
Jensen V 1981 Heterotrophic micro-organisms.In Nitrogen Fixation, Vol. 1: Ecology. Ed. W J Broughton pp 30–56. Clarendon Press, Oxford.
Kapustka L A and Rice E L 1978 Acetylene reduction (N2-fixation) of glucose-amended soils from central Oklahoma old field succession plots. South. Natur. 23, 389–396.
Mulder E G 1975 Physiology and ecology of free-living, nitrogen-fixing bacteria.In Nitrogen Fixation by Free-living Microorganisms. Ed. W D P Stewart. pp 3–28. Cambridge University Press, Cambridge.
Neyra C A and Döbereiner J 1977 Nitrogen fixation in grasses.In Advances in Agronomy, Vol. 29. Ed. N C Brady pp 1–38. Academic Press, London.
Okon Y and Hardy R W F 1983 Developments in basic and applied biological nitrogen fixation.In Plant Physiology: A Treatise, Vol. 8. Ed. F C Steward, pp 5–54. Academic Press, Orlando.
O'Toole P and Knowles R 1973 Efficiency of acetylene reduction (nitrogen fixation) in soil: Effect of type and concentration of available carbohydrate. Soil Biol. Biochem. 5, 789–797.
Rennie R J 198015N-isotope dilution as a measure of dinitrogen fixation byAzospirillum brasilense associated with maize. Can. J. Bot. 58, 21–24.
Rovira A D, Foster R C and Martin J K 1979 Note on terminology: Origin, nature and nomenclature of the organic materials in the rhizosphere.In The Soil-Root Interface. Eds. J C Harley and R S Russell. pp 1–14. Academic Press, London.
Stewart W D P 1982 Nitrogen fixation — its current relevance and future potential. Israel J. Bot. 31, 5–44.
Thompson J P and Skerman V B D 1979 Azotobacteraceae: The Taxonomy and Ecology of the Aerobic Nitrogen-fixing Bacteria. Academic Press, London. pp 357–368.
Zuberer D A and Alexander D B 1986 Effects of oxygen partial pressure and combined nitrogen on N2-fixation (C2H2) associated withZea mays and other gramineous species. Plant and Soil 90, 47–58.
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Alexander, D.B., Zuberer, D.A. Effects of organic substrates and chloramphenicol or nalidixic acid on acetylene reduction associated with roots of intact maize and sorghum plants. Plant Soil 112, 61–67 (1988). https://doi.org/10.1007/BF02181753
- acetylene reduction
- nitrogen fixation
- organic substrates
- oxygen partial pressure
- Sorghum bicolor
- Zea mays