Phosphorus-induced micronutrient disorders in hybrid poplar |
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Authors: | Victor R Timmer Yuanxin Teng |
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Institution: | (1) Department of Microbiology, Wageningen Agricultural University, Hesselink van Suchtelenweg 4, 6703 CT Wageningen, The Netherlands |
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Abstract: | The effect of calcium on the nodulation of lucerne was studied using EGTA, a specific calcium-chelator. First, the effects
of the chelator were tested on hydroponically grown plants at pH 7.0. Optimal numbers of nodules were obtained in nutrient
solution containing 0.2 mM CaCl2. When 0.4 mM EGTA was given additionally, nodulation was completely inhibited. Nodulation was restored specifically with CaCl2, but not with MgCl2.
For studies in an acid soil (pH-H2O 5.2), lucerne seedlings were grown in rhizotrons. 67% of the seedlings became nodulated when the soil around the seed was
neutralized locally with 1.0 μmol of K2CO3 in drops of 12 μL volume. When native calcium was removed with 2 μmol of EGTA, nodulation was reduced to 12%. However, addition of EGTA to soil resulted in a drop of pH from 6.1 to 5.2. A
phosphate buffer could also not keep soil-pH sufficiently stable. Such pH-decreases could be avoided by placing agar blocks
containing 6 μmol of EGTA for three hours on freshly developed roots. This treatment reduced nodulation from 87% to 32%, with soil-pH lowering
only from 6.2 to 6.0. Nodulation could be restored by adding 2 μmol of CaCl2. The depletion of soil-calcium could depress nodule formation only during the first day after inoculation. |
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Keywords: | chelation EGTA calcium Medicago sativa L nitrogen fixation Rhizobium meliloti rhizotron |
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