Effect of Bentazon, a Hill Reaction Inhibitor, on Symbiotic Nitrogen-fixing Capability and Apparent Photosynthesis |
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| Authors: | Bethlenfalvay G J Norris R F Phillips D A |
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| Affiliation: | Departments of Agronomy and Range Science, and Botany, University of California, Davis, California 95616. |
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| Abstract: | Symbiotic associations of bean plants (Phaseolus vulgaris L. cv. Blue Lake) and Rhizobium phaseoli strain 127K17 were treated with the Hill reaction inhibitor bentazon (3-isopropyl-1 H-2,1,3-benzothiadiazin-4-(3H)-one-2,2-dioxide). Plants receiving foliar and root treatments of 1.8 kilograms per hectare bentazon were assayed at 6 hour intervals for N2-fixing capacity by measuring C2H2-dependent C2H4 production and H2 evolution and for CO2 exchange rates. In foliar treated plants greatest measured inhibition of CO2 exchange rates and N2-fixing capacity occurred 6 and 12 hours after treatment, respectively. In root-treated plants maximum inhibition of both processes was delayed by 6 hours, and was less severe than in foliar treated plants. Nitrogen-fixing capacity and CO2 exchange rate recovered to control levels in all plants. Application of higher rates of bentazon resulted in greater inhibition of CO2 exchange rate and N2-fixing capacity. Inhibition of the two processes was positively correlated (r = 0.985). The results indicate that inhibition of N2-fixing capacity was not caused by bentazon directly, but indirectly through limiting the availability of photosynthate to support root nodule activity. |
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