title: Impact of rhizobial inoculation and reduced N supply on biomass production and biological N2fixation in common bean grown hydroponically.
abstract: BACKGROUND
  Testing rhizobial inoculation of common bean (Phaseolus vulgaris L.) in hydroponics enables accurate quantification of biological N2fixation (BNF) and provides information about the potential of reducing inorganic N fertilizer use. In view of this background, common bean grown on pumice was inoculated with Rhizobium tropici CIAT899 (Rt) and supplied with either full-N (total nitrogen 11.2 mmol L-1), 1/3 of full-N or N-free nutrient solution (NS). BNF was quantified at the early pod-filling stage using the15N natural abundance method.
  
  
  RESULTS
  Full-N supply to Rt-inoculated plants resulted in markedly smaller nodules than less- or zero-N supply, and no BNF. Rt inoculation of full-N-treated plants did not increase biomass and pod yield compared with non-inoculation. Restriction (1/3 of full-N) or omission of inorganic N resulted in successful nodulation and BNF (54.3 and 49.2 kg N ha-1, corresponding to 58 and 100% of total plant N content respectively) but suppressed dry shoot biomass from 191.7 (full-N, +Rt) to 107.4 and 43.2 g per plant respectively. Nutrient cation uptake was reduced when inorganic N supply was less or omitted.
  
  
  CONCLUSIONS
  Rt inoculation of hydroponic bean provides no advantage when full-N NS is supplied, while 1/3 of full-N or N-free NS suppresses plant biomass and yield, partly because the restricted NO3-supply impairs cation uptake. © 2017 Society of Chemical Industry.
authors.affiliation: Department of Crop Science, Agricultural University of Athens, Iera Odos, Athens, Greece.
authors.forename: Charis-Konstantina
authors.initials: CK
authors.lastname: Kontopoulou
authors.affiliation: Department of Crop Science, Agricultural University of Athens, Iera Odos, Athens, Greece.
authors.forename: Epifanios
authors.initials: E
authors.lastname: Liasis
authors.affiliation: The James Hutton Institute, Invergowrie, Dundee, UK.
authors.forename: Pietro Pm
authors.initials: PP
authors.lastname: Iannetta
authors.affiliation: Department of Crop Science, Agricultural University of Athens, Iera Odos, Athens, Greece.
authors.forename: Anastasia
authors.initials: A
authors.lastname: Tampakaki
authors.affiliation: Department of Crop Science, Agricultural University of Athens, Iera Odos, Athens, Greece.
authors.forename: Dimitrios
authors.initials: D
authors.lastname: Savvas
mesh_terms: D059827:Agricultural Inoculants / Q000502:physiology*; D018533:Biomass; D005308:Fertilizers / Q000032:analysis; D018527:Hydroponics; D009584:Nitrogen / Q000378:metabolism*; D009586:Nitrogen Fixation; D027805:Phaseolus / Q000382:microbiology / Q000502:physiology*; D012231:Rhizobium / Q000502:physiology*; D013559:Symbiosis
chemical_list: D005308:Fertilizers; D009584:Nitrogen
keywords: Phaseolus vulgaris; Rhizobium tropici; nitrogen; soilless culture; yield