Stimulation of nodulation in field peas (Pisum sativum) by low concentrations of ammonium in hydroponic culture.
Although the inhibitory effects of high concentrations of mineral N (> 1.0 mM) on nodule development and function have often been studied, the effects of low, static concentrations of NH4+ (< 1.0 mM) on nodulation are unknown.  In the present experiments we examine the effects of static concentrations of NH4+ at 0, 0.1 and 0.5 mM in flowing, hydroponic culture on nodule establishment and nitrogenase activity in field peas [Pisum sativum L. cv. Express (Svalöf AB)] for the initial 28 days after planting (DAP).  Peas grown in the presence of low concentrations of NH4+ had significantly greater nodule numbers (up to 4-fold) than plants grown without NH4+.  Nodule dry weight per plant was significantly higher at 14, 21 and 28 DAP in plants grown in the presence of NH4+, but individual nodule mass was lower than in plants grown without NH4+.  The nodulation pattern of the plants supplied with NH4+  was similar to that often reported for supernodulating mutants, however the plants did not express other growth habits associated with supernodulation.  Estimates of N2 fixation indicate that the plus-NH4+ peas fixed as much or more N2 than the plants supplied with minus-NH4+ nutrient solution.  There were no significant differences in nodule numbers, nodule mass or NH4+ uptake between the plants grown at the two concentrations of NH4+.  Nodulation appeared to autoregulate by 14 DAP in the minus-NH4+ treatment.  Plant growth and N accumulation in the minus-NH4+ plants lagged behind those of the plus-NH4+ treatments prior to N2 fixation becoming well established in the final week of the experiment.  The plus-NH4+ treatments appeared not to elicit autoregulation and plants continued to initiate nodules throughout the experiment.
Waterer
J G
JG
Dept of Plant Science, Univ. of Manitoba, Winnipeg, Canada.
Vessey
J K
JK
Raper
C D
CD
D003470:Culture Media; D018527:Hydroponics; D009584:Nitrogen / Q000378:metabolism*; D009586:Nitrogen Fixation / Q000187:drug effects*; D018532:Pisum sativum / Q000187:drug effects* / Q000254:growth & development* / Q000378:metabolism; D018517:Plant Roots / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology*; D016961:Rhizobium leguminosarum; D013997:Time Factors
D003470:Culture Media; D000644:Quaternary Ammonium Compounds; D009584:Nitrogen