不同氮源对黑松幼苗根-土界面无机磷形态转化及有效性的影响

Effects of Different Nitrogen Sources on Transformation and Availability of Inorganic Phosphorus in the Root-Soil Interface of Pinus thunbergii Seedlings

用根垫-冰冻切片法研究不同氮源对石灰性潮土中黑松幼苗根-土界面无机磷形态转化及有效性的影响。结果表明:铵态氮(NH4+-N)处理后幼苗根-土界面pH值较对照处理明显降低,而硝态氮(NO3--N)处理后幼苗根-土界面pH值较对照处理升高,不同氮源引起的幼苗根-土界面pH值变动的幅度取决于氮源的质量分数。铵态氮处理明显降低了幼苗根-土界面Ca2-P,Fe-P和Al-P质量分数,100,200和400mg·kg-1的铵态氮处理后,距根表0～1mm处Ca2-P较土体亏缺率分别为37.1%,45.9%和57.7%,Fe-P较土体亏缺率分别为23.4%,29.1%和38.2%,Al-P较土体亏缺率分别为25.1%,28.0%和33.2%;硝态氮处理增加了幼苗根-土界面Ca2-P,Fe-P和Al-P质量分数,但不显著。铵态氮与硝态氮处理后幼苗根-土界面Ca8-P的亏缺程度较对照分别加大或降低,但不明显。铵态氮与硝态氮处理后幼苗根-土界面Ca10-P和O-P质量分数较对照处理变化很小。铵态氮引起的黑松幼苗根-土界面pH值的降低,促进了幼苗根-土界面处无机磷的形态转化,提高了根-土界面无机磷的生物有效性,显著增加了根系对磷的吸收。

The calcareous fluvoaquic soil was collected and a microcosm study was carried out with rootmat and frozen slicing method in laboratory. The pH in the rootsoil interface with the control treatment was just slightly lower than in the bulk soil. However, the addition of NH4 N significantly decreased the pH value in the rootsoil interface and the addition of NO3 N slightly increased the pH value in the rootsoil interface. The magnitude of pH changes in the rootsoil interface depended upon the concentrations of the nitrogen sources added. The contents of Ca2P, FeP and A1P in the rootsoil interface were much lower after treated with NH4＋ N and slightly higher after treated with NO3 N compared with control treatment. After treated with 100, 200 and 400 mg.kg1 NH4 N, the deficiency rates of Ca2P in the area 0 1 mm from the root plane were 37.1% , 45.9% and 57.7% , respectively, the deficiency rates of FeP were 23.4% , 29. 1% and 38.2% , respectively, and the deficiency rates of A1P were 25.1% , 28.0% and 33.2% , respectively. Compared with the control the deficiency rates of CasP in NH4 N and NO3 N treatments decreased and increased, respectively, but the differences were not obvious. The contents of Cal0P and OP in the rootsoil interface did not significantly change after treated with NH4＋N or NO3N, suggesting that Cal0P and OP were remarkably difficult to be mobilized even at the presence of high concentration of NH4＋N. The lowered pH in the rootsoil interface induced by the addition of the NH N promoted the transformation of phosphates in the rootsoil interface, enhanced the mobilization and bioavailability of phosphates, and thereby remarkably increased the absorption of phosphorus by roots.