Effect of C, N sources and C/N ratio on the solubilization of rock phosphate by some microorganisms

Some phosphate solubilizing microorganisms were grown in liquid medium cultures with different nitrogen materials (NH + 4, NO - 3, urea), carbon materials (glucose, sucrose, molasses, starch) and C/N ratios (34∶1, 20∶1, 5∶1). Of the eight isolates tested,two isolates of Aspergillus sp. 2TCiF2 and 4TCiF6 had much higher capacity to dissolve rock phosphate when supplying with NO - 3 than with either NH + 4 or urea. However, Arthrobacter sp.1TCRi7 and 1TCRi14 decreased their activities of dissolving rock phosphate at NO - 3 medium. Other isolates of Penicillium sp.1TCRiF5 and 2TCRiF4, Enterobacter sp.1TCRi15 and Erwinia sp.4TCRi22 showed strong ability to solubilize rock phosphate only at NH + 4 medium. Little effect was found on phosphate solubilization when adding a small amount of available phosphate in the culture media. Carbon sources had strong influence on rock phosphate solubilization. The fungus of Penicillium sp.2TCiF2 showed the highest capacity to dissolve the rock when supplying sucrose. However, a bacterium of Arthrobacter sp.1TCRi7 had this ability only in the glucose medium. The isolates of Aspergillus sp. and Erwinia sp. had higher capacity of phosphate solubilization in larger C/N ratios of the media, but Penicillium sp. and Enterobacter sp. showed the highest activity in the lowest C/N ratio. The effect of C/N ratios was little in phosphate solubilization of Arthrobacter sp. It is supposed that complexion of organic acids with metals may be the main reason for these isolates to solubilize the phosphate. In particular, other chelant substances may be much more important for Enterobacter sp. and Erwinia sp. to release P from the rock phosphate. Metabolisms and especially secretion of the nature of the organic acids by these microorganisms were greatly affected by nitrogen sources, carbon sources and C/N ratios.