Effects Of Growing Phytase Transgenic Corn On The Compositions And Contents Of Soil Phosphorus

Phytase transgenic corn (PT) can improve the P utilization efficiency of the monogastric animals. However, growing PT also raises ecological concerns with respect to potential adverse effect on the dynamics of soil P content and composition. On one hand, PT directly affected soil P levels through release of phytase into soil. On the other hand, the changes in chemical composition or quality from straw and other crop residual return will further affect the soil biological communities and activity in the field, which will affect the process of fixed and mineralization of soil inorganic and organic P release. Based on the fact that transgenic crops affected soil fertility by routes growing and decomposition of residues, this study investigated the effected of phytase transgenic corn on soil fertility (especially soil phosphorus) by means of field experiment and greenhouse experiment.A two-year field experiment was conducted to investigate the effect of phytase transgenic corn (BVLA430101) and its corresponding parent lines (Yingyu 35) on soil fertility, the main results from our field investigation were as follows:1) Compared to soil grown with its isogenic corn, the effects of PT on soil P varied with the specific sampling times and P fractions, three years’continuously growing PT had significant influences on labile P fractions, moderately labile P fractions in soil at several specific growth stages. Growing PT had no significant effects on the contents of diluted HCl extractable inorganic P (Dil.HCl-Pi), concentrated HCl extractable inorganic P (Conc.HCl-Pi), concentrated HCl extractable organic P (Conc.HCl-Po) and Residual P (Residual-P). Compared to its isogenic corn, the phytase activity was significant higher in soil grown with PT during the two years’investigation, and the alkaline phosphatase activity significantly increased before 2012 planting stage and in the followed 2013 growing period. And the urease activity significantly decreased in 2012 maturity stage, 2013 heading stage and maturity stage. The invertase activity significantly decreased in 2013 all sampling times. The PT had a significant effect on the content of souble P, souble K at several samplings, but such effect was not sustained; And the PT had no effect on pH, total P, organic C and total N contents.2) The shoot and root P contents of PT was significant higher than its isogenic corn. The shoot N content significantly decreased due to PT at maturity stage in 2012 and 2013, and the root N content significantly decreased by PT at maturity stage in 2012, heading and maturity stages in 2013. The PT had no significant effect on K content of shoot and root in 2-year’s samplings.Based on facterial design with different P sources, arbuscular mycorrhizal fungi (AMF), a greenhouse experiment was conducted to investigate the effect of phytase transgenic corn and its isogenic corn on soil phosphorus content. The main results were as follows:1) Compared to soil grown with its isogenic corn, the effects of PT on soil P varied with the specific P sources and the inoculation of AMF. PT significantly increased the contents of soil MBP, NaHCO3-Pi, NaOH-Pi and NaOH-Po when the soil inoculated with AMF, and decreased the content of H2O-Pi, Conc.HCl-Po. The contents of MBP, Conc.HCl-Po significantly increased due to PT in the soil without AMF inoculation. The influences of PT on soil phosphorus fractions varied with P sources. Amending phytate-Na increased soil organic phosphorus, while NaH2PO4 increased soil inorganic phosphorus. Amending P have greater effect on soil labile P fractions and moderately labile P fractions than insoluble P fractions. The insoluble P fractions and some organic P fractions were decreased by inoculation with AMF. P sources, AMF and their interaction with PT has significant effects on most P fractions. The PT increased the activities of soil phytase and alkaline phosphatase, and Phytate-Na increased phytase and alkaline phosphatase. Compared with its isogenic corn, PT has no effect on soil invertase activity. The PT significantly decreased the urease activity if inocubated with AMF. The PT tended to decrease the content of soil suble P and total P.2) The shoot and root P contents were significantly increased by PT, and increased the contents of shoot and root P if NaH2PO4 and AMF added. The PT has no effect on N, K contents fo shoot and root. Compared with its isogenic corn, PT increased the shoot biomass, especially under the condition with NaH2PO4 and AMF inoculated.In conclusion, growing PT had significant effects on labile P fractions, moderately labile P fractions in soil at specific growth stage in the field experiment. From the greenhouse experiment with different P sources and AMF inoculation, the impacts of PT on soil organic phosphorus were higher than those on inorganic phosphorus, in particular for moderately labile and insoluble organic phosphorus fraction. Our results indicated that soil phosphorus was modified through release phytase from both field and greenhouse experiment. Future work should also take account of combining different soil properties via long-term monitoring at different sites.