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The calcareous fluvo-aquic soil was collected and a microcosm study was carried out with root-mat and frozenslicing 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 Ca_2-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 Ca_2-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 Ca_8-P in NH_4~+ -N and No_3-N treatments decreased and increased,respectively,but the differences were not obvious.The contents of Ca_(10) -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 Ca_(10)- 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.
The calcareous fluvo-aquic soil was collected and a microcosm study was carried out with root-mat and frozenslicing method in laboratory. The pH in the root-soil interface with the control treatment was just slightly lower than in the bulk soil. 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 Ca_2-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, respectively, the deficiency rates of Ca_2-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 respectively. Compared with the control of the deficiency rates of Ca_8-P in NH_4 ~ + -N and No_3-N treatments decreased and increased, respectively, but the differences were not obvious. contents. of the 25.1%, 28.0% and 33.2% Suggesting that Ca_ (10) -P and OP in the root-soil interface did not change change after treated with NH_4 ~ + -N or No_3 -N, suggesting that Ca_ (10) -P and OP were remarkably difficult to be mobilized even at the presence of high concentration of NH_4 ~ + -N. The enhanced 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 remark remarkably increased the absorption of phosphorus by roots.