关键词: 落叶松苗木, 根/土界面, N素形态, pH值, 养分有效性

Abstract:

The effect of different nitrogen and phosphorus sources on pH and the availability of mineral nutrients in the root/soil interface of Larix gmelinii seedlings were studied by means of root-mat method. The results showed that the addition of NH⁺₄-N decreased the pH in the root/soil interface, while the addition of NO^-₃-N increased the pH in contrast with the control treatment. The sort of the P sources and the distance from the root plane remarkably influenced the changes of pH in the root/soil interface induced by the addition of the nitrogen sources. Compared with the addition of only NH⁺₄-N, the extent to which the pH in the root/soil interface decreased was obviously smaller when treated by NH⁺₄-N and rock P. When treated with different P sources, the contents of available P in the root/soil interface were affected by the sort of the N sources. When treated with soluble P, the contents of the available P in the root/soil interface obviously increased for the addition of both NH⁺₄-N and NO₃^--N. When treated with rock P, the contents of the available P increased only in the area 0～3 mm from the root plane for NH⁺₄-N, whereas the contents of available P in the root/soil interface changed little for NO₃^--N. The results above showed that the protons excreted by the roots were the main driving force for the solution of the rock P in the root/soil interface. The availability of Fe in the root/soil interface increased as a result of acidity induced by the NH⁺₄-N, whereas the availability of Fe in the root/soil interface decreased because of the pH increase induced by the NO₃^--N. The effect of different N sources on the availability of Fe in the root/soil interface was also affected by the sort of P sources. The concentrations of P、Fe in the leaves remarkably differed when treated by different N、P sources and concentrations of the P、Fe in the root/soil interface were correlated to those in the leaves of the seedlings.

Key words: Larix gmelinii seedlings, root/soil interface, nitrogen sources, pH, nutrient availability