title: P-deficiency increases the O2 uptake per N2 reduced in alfalfa.
abstract: Nodulated alfalfa (Medicago sativa L. cv. Saranac) plants were grown in hydroponics at P-sufficient and P-deficient supply levels. After 5 weeks of growth, dry matter accumulation, nodulation, total N and P accumulation, as well as 15N2 uptake, were measured. Moreover, the response of nodule O2-uptake to raising external pO2 was determined in an open-flow measurement system and nodule permeability was calculated. Plants in the P-deficient supply treatment had a lower P concentration in all organs. In both treatments the highest P concentration was found in nodules. In the P-deficient supply treatment plants formed less dry matter, had a lower shoot/root ratio, less nodulation, decreased total N accumulation, and lower 15N2 uptake per dry matter nodule. Nodules in the P-deficient treatment were, on average, smaller and had a higher O2 uptake per N2 reduced, coinciding with increased nodule permeability and conductance. Thus increased oxygen uptake appears to be a mechanism to adjust nodule metabolism to P deficiency in indeterminate N2-fixing nodules such as in alfalfa, as has previously been shown for determinate nodule forms.
authors.affiliation: Institut für Agrikulturchemie der Georg-August-Universität Göttingen, Carl-Sprengel-Weg 1, D-37075 Göttingen, Germany. jschulz2@gwdg.de
authors.forename: Joachim
authors.initials: J
authors.lastname: Schulze
authors.forename: Jean-Jacques
authors.initials: JJ
authors.lastname: Drevon
mesh_terms: D001692:Biological Transport; D000455:Medicago sativa / Q000378:metabolism*; D009584:Nitrogen / Q000378:metabolism*; D010101:Oxygen Consumption / Q000502:physiology*; D010758:Phosphorus / Q000502:physiology*; D018517:Plant Roots / Q000378:metabolism / Q000382:microbiology; D018520:Plant Shoots / Q000378:metabolism
chemical_list: D010758:Phosphorus; D009584:Nitrogen