Pea roots affect immobilisation and solubilisation of phosphorus depending on genotype, stage and phosphorous source.

To assess the efficiency of pea roots to mobilize available phosphorus (P) from P compounds we subjected various pea genotypes to a post-treatment method. Axenic seedlings were raised on P-deficient semisolid synthetic medium using control blanks without a plant otherwise treated in the same way. AlPO(4), CaHPO(4), FePO(4), apatite and meat-bone-meal (MBM) were tested. A genotype was tested from 1-day through 15-days of growth. There were differences between the compounds (p < 0.001). P was dissolved from CaHPO(4) with apparent maxima at 72-h intervals and to a significantly lesser extent from MBM. With AlPO(4), FePO(4) and apatite, the roots did not show a dissolving effect, but, on the contrary, significantly immobilised P. In each case a correlation with an increase in acidity, H(+) (p < 0.001) was observed. The correlation was negative in the AlPO(4), FePO(4) and apatite series. A CaHPO(4) treatment combined with apatite or MBM significantly decreased solubility of P from that of CaHPO(4) singly. Tests with six additional genotypes showed that all solubilised P from CaHPO(4), some to a significant extent from apatite, MBM or slightly from FePO(4), but none from AlPO(4). The accumulation of nearly water-insoluble aluminium and iron phosphates in field and virgin soils is partly explainable by the immobilisation through the root action on P, which we have found also with other plant species. The root responses must also have ecophysiological functions distinct from P acquisition.