Associative N2-fixation in plants growing in saline sodic soils and its relative quantification based on15N natural abundance |
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Authors: | K A Malik Rakhshanda Bilal G Rasul K Mahmood M I Sajjad |
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Institution: | (1) Department of Microbiology, Wageningen Agricultural University, Hesselink van Suchtelenweg 4, 6703 CT Wageningen, The Netherlands;(2) Department of Field Crops and Grassland Science, Wageningen Agricultural University, The Netherlands;(3) Department of Agronomy and Horticulture, Universiti Pertanian Malaysia, 43400 UPM Serdang, Selangor, Malaysia |
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Abstract: | The interactive effect of low P supply (0, 10, 20 and 40 M) and plant age on nodule number, mass and functioning (ureide analysis technique), vegetative growth and pod production were investigated in glasshouse-grown nodulated cowpea (Vigna unguiculata L.cv. Kausband) in sand culture. Compared with 40 M P, P stress (0 M P) or very low (10 M P) supply markedly impaired nodulation, allantoin and amino-N concentrations and weight of N solutes in xylem exudates. Consequently, P stress reduced top growth and pod yields by 48 and 90%, respectively. N solutes in xylem exudates and total plant N assayed by Kjeldahl technique (as estimates of N2 fixation) responded similarly to P supply. However, the relative ureide index (ureide-N/ureide N+amino-N)×100] remained constant (99%), irrespective of P supply, indicating the plants' complete dependency on symbiosis for growth, without implying that growth was markedly increased by N2 fixation. Although P concentrations in plant tops, roots and nodules increased with P supply, N concentrations in these plant tissues were unaffected by P supply. The concentrations of N and P in the nodules were 2–2 1/2 times higher than in plant tops. P application interacted strongly with plant age, with the largest P effect evidently achieved at the early podding stage. The significance and implications of these results are discussed. |
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Keywords: | allantoin amino-N nodule size N-free nutrient solution P deficiency stress sand culture xylem exudate |
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