The Contribution of Atmospheric N_2 to Azolla spp. Grown on Flooded Soils

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概要

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• The contribution of atmospheric N_2 (Ndfa) to Azolla growth in flooded rice soils was studied by the ^<15>N dilution method. thirty days after the addition of ^<15>N-labeled N to a soil (Maahas clay), Azolla pinnata was grown in three consecutive croppings with (2nd cropping) and without (first and third croppings) rice canopy. Lemna minor was used as a non-N_2-fixing reference plant. when the carryover of N from the inoculum was not negligible, the ^<15>N isotope composition in the harvested plant material was corrected by the equation [numerical formula] Since the growth of Lemna was very poor in the first and third croppings of Azolla, the carryover of unlabeled N from the inoculum was large and the corrected ^<15>N abundance value in Lemna was abnormal. Lemna, therefore, could not be used as a reference plant. In the first cropping green alga which grew as a contaminant was used as reference and the value of Ndfa was 88%. In the second cropping, where the growth of Azolla and Lemna was reasonably good, the value of Ndfa was estimated at 86%. In another soil (Luisita sand), ^<15>N-labeled N was added and one crop of rice was grown to reduce the temporal change of ^<15>N abundance in available N. Then, A. pinnata, A. microphylla, and A. filiculoides were grown using Anabaena-free A. filiculoides and Lemna as non-N_2-fixing reference plants. Since the growth of Anabaena-free Azolla was poor, this plant could not be used as a reference. The value of Ndfa among Azolla strains did not differ, and was about 80%. The ^<15>N isotope composition in NH_4^+-N in the soil was similar to the isotope composition in the reference plant and could be used as a substitute of non-N_2-fixing reference. In the same soil, Azolla and the reference plants were grown without the addition of ^<15>N-labeled substrate. Based on the natural ^<15>N abundance the value of Ndfa of A. filiculoides was estimated at 75% and that of A. nilotica was 96%. Determinations of the natural ^<15>N abundance of Azolla and aquatic plant samples grown in ponds and rice fields in Japan and the Philippines also showed that the value of Ndfa was higher than 75%.

• 社団法人日本土壌肥料学会の論文

著者

• Ventura Wilbur

  Soil Microbiology Division The International Rice Research Institute

• Yoneyama Tadakatsu

  National Agricultural Research Center For Tohoku Region

• WATANABE Iwao

  Soil Science and Plant Nutrition Laboratory, Faculty of Bioresources, Mie University

• Talukdar Haridev

  Assam Agricultural University

• Watanabe Iwao

  Soil Microbiology Department International Rice Research Institute

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• 24-11 Metabolism of Acetate and Propionate in Anaerobic Rice Soil
• NATURAL ^N ABUNDANCE OF FIELD GROWN SOYBEAN GRAINS HARVESTED IN VARIOUS LOCATIONS IN JAPAN AND ESTIMATE OF THE FRACTIONAL CONTRIBUTION OF NITROGEN FIXATION
• Estimation of N_2 Fixation of Soybean by Comparison of Different ^N Labeling Methods
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• ^N STUDY ON THE FATE OF FOLIARLY APPLIED UREA NITROGEN IN TEA PLANT : Camellia sinensis L.
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