Use of 15N isotope dilution for quantification of N2 fixation associated with roots of kallar grass (Leptochloa fusca (L.)) |
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| Authors: | K A Malik Y Zafar R Bilal E Azam |
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| Institution: | (1) Soil Biology Division, Nuclear Institute for Agriculture and Biology, Rang Road, P.O. Box 128, Faisalabad, Pakistan |
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| Abstract: | Summary
Leptochloa fusca (L.) Kunth (kallar grass) has previously been found to exhibit high rates of nitrogen fixation. A series of experiments to determine the level of biological nitrogen fixation using 15N isotopic dilution were carried out in nutrient solution and saline soil. In the nutrient solution, E. coli inoculated plants were taken as non-nitrogen-fixing control. It was observed that nearly 60%–80% of the plant N was derived from atmospheric fixation. Estimations based on the N difference method gave much lower values (18%–35%). In experiments with saline soil which was initially sterilized with chloroform fumigation, a mixed culture of N2-fixing rhizospheric isolates from kallar grass roots was inoculated and planted to kallar grass. Uninoculated treatments were regarded as controls. The soil was previously labelled with 15N by adding cellulose and (15NH4)2SO4. The results of these studies showed fixation values of 6%–32% when estimated by 15N dilution, whereas by the N difference method 54% of the plant N was estimated to be derived from fixation. This discrepancy is due to the increase in root proliferation due to inoculation, which results in greater uptake of soil N. The distribution of 15N in different fractions of the soil-N indicted isotopic dilution due to bacterial fixation of atmospheric N2. |
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| Keywords: | Kallar grass 15N isotopic dilution N2-fixation |
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