Effects of different nitrogen and phosphorus sources on pH and availability of P in the root/soil interface of Pinus koraiensis seedlings

The effects of different nitrogen and phosphorus sources on pH and P availability in the root/soil interface of Korean pine seedlings were studied by means of the root-mat method. The results show that the addition of NH₄⁺-N decreases the pH in the root/soil interface, while the addition of NO₃^--N increases the pH compared with the control treatment. The type of P sources and the distance from the root plane reamarkably influence the changes of pH in the root/soil interface induced by the addition of the nitrogen sources. Compared with the addition of only NH₄⁺-N, the extent to which the pH in the root/soil interface decreases is obviously smaller when treated by NH₄⁺-N and rock P. When treated with different P sources, the contents of available P in the root/soil interface are affected by the types of the N sources. The content of the available P in the root/soil interface obviously increases when treated with NH₄⁺-N and soluble P, whereas the content of the available P increases only in the area 1-2 mm from the root plane when treated with NH₄⁺-N and rock P. When treated with NO₃^--N, the contents of available P in the root/soil interface increase only when applied with soluble P, whereas the contents of the available P change little when applied with rock P. The results above show that the protons excreted by the roots are the main activating force for the solution of the rock P in the root/soil interface. The concentrations of P in the root/soil interface are remarkably correlated with those in the needles of the seedlings.