Nitrogen Fixation in the Phyllosphere of Tropical Plants: Occurrence of Phyllosphere Nitrogen-Fixing Micro-organisms in Eastern India and their Utility for the Growth and Nitrogen Nutrition of Host Plants

Of the 560 leaf samples belonging to 259 species of green plants examined more than 50 per cent of the Angiosperms and 25 per cent of the Pteridophytes and Gymnosperms revealed the presence of N2-fixing micro-organisms in their phyllosphere. Plants particularly remarkable in this respect are orchids and several other epiphytes, Scindapsus officinalis, Ficus and cucurbits. Most of the isolates appear to be biotypes of Klebsiella pneumoniae. The more active strains fixed more than 5 mg N g−1 glucose utilized and reduced more than 100 nmol C2H2 mg−1 cell d. w h−1. The efficacy of the phyllosphere N2-fixing isolates for N-nutrition of host plants was studied by spraying suspensions of the cultures grown on N-free media on rice and wheat seedlings. In IR-26 rice or Sonalika and Janak wheat grown on soil in wooden flats or earthenware pots, 22 per cent of the 161 cultures studied caused increased height and about three-quarters of the cultures enhanced dry weight by more than 50 per cent; chlorophyll and N-contents were enhanced more than 50 per cent by about half and two-thirds of the cultures respectively. In N-free sand culture 26 of the 50 promising strains doubled N-content, and 30 doubled dry weight of the tested plants. In some cases dry weight, number of grains per panicle, and 1000 grain weight were increased by 300, 70–83 and 126–158 per cent respectively; N-content of straw and seed was increased three- or fourfold. In several cases the beneficial effects were found to match closely the performance of plants receiving ammonium sulphate.