AOBPreview originally published online on July 19, 2006
Annals of Botany 2006 98(4):731-740; doi:10.1093/aob/mcl154
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Nitrogen Fixation by White Lupin under Phosphorus Deficiency
1 Department of Crop Science, Plant Nutrition, Georg-August-University Göttingen, Carl-Sprengel-Weg 1, D-37075 Göttingen, Germany, 2 Department of Soil, Water and Climate, University of Minnesota, 1991 Upper Buford Circle, St Paul, MN 55108-6026, USA, 3 Department of Agronomy and Plant Genetics, University of Minnesota, 1991 Upper Buford Circle, St Paul, MN 55108-6026, USA, 4 Viterbo University, Biology Department, 815 Ninth Street South, LaCrosse, WI 54601, USA, 5 Forage Genetics International, N5292 South Gills Coulee Road, West Salem, WI 54669, USA, 6 Institute of Soil Science and Plant Nutrition, Martin-Luther-University Halle-Wittenberg, Adam-Kuckhoff-Str. 17b, 06108 Halle/Saale, Germany and 7 United States Department of Agriculture, Agricultural Research Service, Plant Science Research Unit, St Paul, MN 55108-6026, USA
* For correspondence. E-mail jschulz2{at}gwdg.de
Received: 19 December 2005 Returned for revision: 1 March 2006 Accepted: 5 June 2006 Published electronically: 19 July 2006
• Background and Aims White lupin is highly adapted to growth in a low-P environment. The objective of the present study was to evaluate whether white lupin grown under P-stress has adaptations in nodulation and N2 fixation that facilitate continued functioning.
• Methods Nodulated plants were grown in silica sand supplied with N-free nutrient solution containing 0 to 0·5 mM P. At 21 and 37 d after inoculation (DAI) growth, nodulation, P and N concentration, N2 fixation (15N2 uptake and H2 evolution), root/nodule net CO2 evolution and CO2 fixation (14CO2 uptake) were measured. Furthermore, at 21 DAI in-vitro activities and transcript abundance of key enzymes of the C and N metabolism in nodules were determined. Moreover, nodulation in cluster root zones was evaluated.
• Key Results Treatment without P led to a lower P concentration in shoots, roots, and nodules. In both treatments, with or without P, the P concentration in nodules was greater than that in the other organs. At 21 DAI nitrogen fixation rates did not differ between treatments and the plants displayed no symptoms of P or N deficiency on their shoots. Although nodule number at 21 DAI increased in response to P-deficiency, total nodule mass remained constant. Increased nodule number in P-deficient plants was associated with cluster root formation. A higher root/nodule CO2 fixation in the treatment without P led to a lower net CO2 release per unit fixed N, although the total CO2 released per unit fixed N was higher in the treatment without P. The higher CO2 fixation was correlated with increased transcript abundance and enzyme activities of phosphoenolpyruvate carboxylase and malate dehydrogenase in nodules. Between 21 and 37 DAI, shoots of plants grown without P developed symptoms of N- and P-deficiency. By 37 DAI the P concentration had decreased in all organs of the plants treated with no P. At 37 DAI, nitrogen fixation in the treatment without P had almost ceased.
• Conclusions Enhanced nodulation in cluster root zones and increased potential for organic acid production in root nodules appear to contribute to white lupin's resilience to P-deficiency.
Key words: White lupin, Lupinus albus, nitrogen fixation, P deficiency, H2 evolution, 15N2 uptake
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