Microbial Immobilization and Plant Uptake of Different N Forms in Three Forest Types in Shikoku District, Southern Japan

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Soil microbial immobilization and plant uptake of N were evaluated for three forest types in Kochi, Shikoku district. During 196-d laboratory incubation, soil NO_3-N production in the Hinoki cypress forest was negligible for the initial 40 d and then rapidly increased, whereas NO_3-N production was rapid from the beginning in Japanese cedar and deciduous hardwood forests. Microbial immobilization of the labeled ^<15>N decreased in the order of NH_4-N>glycine-N>NO_3-N. The ^<15>N immobilization was higher for soil in the Hinoki cypress forest than other two soils. The delayed NO_3-N production in the Hinoki cypress forest was likely related with low availability of NH_4-N due to NH_4-N immobilization and substantial NO_3-N immobilization. In the field experiment, ^<15>N uptake by roots decreased in the order of NH_4-N>NO_3-N>glycine-N. The absorption of the labeled ^<13>C suggested direct uptake of organic N. The preference of N forms by root uptake was not different among forest types. Trees in three forest types can absorb inorganic and organic forms of N, suggesting trees absorb the N form that is the most abundant in the soil.
社団法人日本土壌肥料学会の論文