The relationship between silicon availability,and growth and silicon concentration of the salt marsh halophyte Spartina anglica |
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Authors: | de Bakker NVJ Hemminga M A Van Soelen J |
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Institution: | (1) Soil and Water Science Department, Faculty of Agriculture, University of Alexandria, El-Shatby, Alexandria, Egypt;(2) Institute of Plant Nutrition, University of Hannover, Herrenhaeuser Street 2, 30419 Hannover, Germany fax |
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Abstract: | Incorporation of cover crops into cropping systems may contribute to a more efficient utilization of soil and fertilizer P
by less P-efficient crops through exudation of P-mobilizing compounds by the roots of P-efficient plant species. The main
objective of the present work was to test this hypothesis. First a method has been developed which allows the quantification
of organic anion exudation from individual cluster roots formed by P-deficient white lupin (Lupinus albus L.). Lupin plants
were grown in nutrient solution at 1 μM P and in a low P loess in small rhizotrons. Organic anions exuded from intact plants
grown in nutrient solution were collected from individual cluster roots and root tips sealed in small compartments by an anion-exchange
resin placed in nylon bags (resin-bags). Succinate was the dominant organic anion exuded followed by citrate and malate. The
mean of citrate exudation-rate was 0.06 pmol mm−1 s−1 with exudation highly dependent on the citrate concentration and on the age of the cluster roots. Exudates from cluster roots
and root tips grown at the soil surface (rhizotron-grown plants) were collected using overlayered resin–agar (resin mixed
with agar). Citrate exudation from cluster roots was 10 times higher than that from root tips. Fractionation of P in the cluster
root rhizosphere-soil indicates that white lupin can mobilize P not only from the available and acid-soluble P, but also from
the stable residual soil P fractions. In pot experiments with an acid luvisol derived from loess low in available P, growth
of wheat was significantly improved when mixed-cropped with white lupin due to improved P uptake. Both in mixed culture and
in rotation wheat could benefit from the P mobilization capacity of white lupin, supporting the hypothesis above. Nine tropical
leguminous cover crops and maize were grown in a pot experiment using a luvisol from Northern Nigeria low in available P.
All plant species derived most of their P from the resin and bicarbonate-extractable inorganic P. Organic P (Po) accumulated particularly in the rhizosphere of all plant species. There was a significant negative correlation between the
species-specific rhizosphere acid phosphatase activity and Po accumulation. Growth and P uptake of maize grown in rotation after legumes were enhanced indicating that improved P nutrition
was a contributing factor.
This revised version was published online in June 2006 with corrections to the Cover Date. |
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Keywords: | cover crops legumes Lupinus albus phosphorus efficiency root exudates rotation |
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