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

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。

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

The calcareous fluvo-aquic soil was collected and a microcosm study was carried out with root-mat and frozen-slicing method in laboratory.The pH in the root-soil interface with the control treatment was just slightly lower than in the bulk soil.However,the addition of NH+4-N significantly decreased the pH value in the root-soil interface and the addition of NO-3-N slightly increased the pH value in the root-soil interface.The magnitude of pH changes in the root-soil interface depended upon the concentrations of the nitrogen sources added.The contents of Ca2-P,Fe-P and Al-P in the root-soil interface were much lower after treated with NH+4-N and slightly higher after treated with NO-3-N compared with control treatment.After treated with 100,200 and 400 mg·kg-1 NH+4-N,the deficiency rates of Ca2-P in the area 0-1 mm from the root plane were 37.1%,45.9% and 57.7%,respectively,the deficiency rates of Fe-P were 23.4%,29.1% and 38.2%,respectively,and the deficiency rates of Al-P were 25.1%,28.0% and 33.2%,respectively.Compared with the control the deficiency rates of Ca8-P in NH+4-N and NO-3-N treatments decreased and increased,respectively,but the differences were not obvious.The contents of Ca10-P and O-P in the root-soil interface did not significantly change after treated with NH+4-N or NO-3-N,suggesting that Ca10-P and O-P were remarkably difficult to be mobilized even at the presence of high concentration of NH+4-N.The lowered pH in the root-soil interface induced by the addition of the NH+4-N promoted the transformation of phosphates in the root-soil interface,enhanced the mobilization and bioavailability of phosphates,and thereby remarkably increased the absorption of phosphorus by roots.