title: The effect of nitrogen nutrition on cluster root formation and proton extrusion by Lupinus albus.
abstract: Nitrogen nutrition can influence cluster root formation in many wild species, but the effect of N form on cluster root formation and root exudation by white lupin is not known. In a solution culture study, we examined the effect of N nutrition (ammonium, nitrate, both or N2 fixation) on cluster root formation and H+ extrusion by white lupin plants under deficient and adequate P supply. The number of cluster roots increased greatly when plants were supplied with I microM P compared with 50 microM P, the increase being 7.8-fold for plants treated with (NH4)2SO4, 3-fold for plants treated with KNO3 and NH4NO3, and 2-4-fold for N2-fixing plants. Under P deficiency. NH4+-N supply resulted in production of a greater number and biomass of cluster roots than other N sources. Dry weight of cluster roots was 30 % higher than that of non-cluster roots in P-deficient plants treated with (NH4)2SO4 and NH4NO3. In plants treated with sufficient P (50 microM), the weight of non-cluster roots was approx. 90 % greater than that of cluster roots. Both total (micromol per plant h(-1)) and specific (micromol g(-1) root d. wt h(-1)) H+ extrusions were greatest from roots of plants supplied with (NH4)2SO4, followed by those supplied with NH4NO3 and N2 fixation, whereas plants receiving KNO3 had negative net H+ extrusion between the third and fifth week of growth (indicating uptake of protons or release of OH- ions). The rate of proton extrusion by NH4+-N-fed plants was similar under P-deficient and P-sufficient conditions. In contrast, proton exudation by N2-fixing plants and KNO3-treated plants was ten-fold greater under P deficiency than under P sufficiency. In comparison with P deficiency, plants treated with 50 microM P had a significantly higher concentration of P in roots, shoots and youngest expanded leaves (YEL). Compared with the N2 fixation and KNO3 treatments, total N concentration was highest in roots, shoots and YEL of plants supplied with (NH4)2SO4 and NH4NO3, regardless of P supply. Under P deficiency, K concentrations in roots decreased at all N supplies, especially in plants treated with (NH4)2SO4 and NH4NO3, which coincided with the greatest H+ extrusion at these P and N supplies. In conclusion, NH4-N nutrition stimulated cluster root formation and H+ extrusion by roots of P-deficient white lupin.
authors.affiliation: Soil Science and Plant Nutrition, The University of Western Australia, Crawley, Australia. lsas@insad.pl
authors.forename: Lidia
authors.initials: L
authors.lastname: Sas
authors.forename: Zed
authors.initials: Z
authors.lastname: Rengel
authors.forename: Caixian
authors.initials: C
authors.lastname: Tang
mesh_terms: D018533:Biomass; D020369:Bradyrhizobium / Q000254:growth & development; D002118:Calcium / Q000378:metabolism; D007887:Fabaceae / Q000187:drug effects / Q000502:physiology*; D007287:Inorganic Chemicals / Q000378:metabolism; D007501:Iron / Q000378:metabolism; D008274:Magnesium / Q000378:metabolism; D008345:Manganese / Q000378:metabolism; D009566:Nitrates / Q000494:pharmacology; D017672:Nitrogen Compounds / Q000494:pharmacology*; D009586:Nitrogen Fixation / Q000502:physiology; D010758:Phosphorus / Q000494:pharmacology; D018517:Plant Roots / Q000187:drug effects / Q000254:growth & development* / Q000378:metabolism; D018520:Plant Shoots / Q000187:drug effects / Q000378:metabolism; D011188:Potassium / Q000378:metabolism; D017494:Proton Pumps / Q000378:metabolism*; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology; D015032:Zinc / Q000378:metabolism
chemical_list: D007287:Inorganic Chemicals; D009566:Nitrates; D017672:Nitrogen Compounds; D017494:Proton Pumps; D000644:Quaternary Ammonium Compounds; D010758:Phosphorus; D008345:Manganese; D007501:Iron; D008274:Magnesium; D015032:Zinc; D011188:Potassium; D002118:Calcium