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Effect of Continuous Glucose Addition on Soil N Transformation of the Pinus tabulaeformis and Cercidiphyllum japonicum Plantations

The glucose solution with different concentrations(0,75,150 and 225 μg C g-1 soil) were continuously added into the soil samples collected from the adjacent Pinus tabulaeformis and Cercidiphyllum japonicum plantations in the upper reaches of Minjiang River.NH4+-N,NO3--N,total dissolved nitrogen(TDN),microbial biomass carbon(MBC),microbial biomass nitrogen(MBN),dissolved organic nitrogen(DON),and net N mineralization rate in the treated soil were determined.For P.tabulaeformis plantation,the addition of 75 μg C g-1soil promoted the net soil N mineralization throughout the 56-day incubation;the 150 μg C g-1 soil C addition only enhanced the net N mineralization after 14 days of the addition and the 225 μg C g-1soil C addition restrained the net N mineralization during the whole incubation period.All glucose addition treatments decreased soil DON content of the P.tabulaeformis plantation,with exception of the 56th day,when the soil DON content showed no significant differences between the 225 μg C g-1 soil treatment and the control.Soil MBN of the P.tabulaeformis plantation in different glucose addition treatments developed different changing tendency over time.For the C.japonicum plantation,the net soil N mineralization was increased by glucose addition of all the three concentrations.At the end of this experiment,soil DON content of the C.japonicum plantation increased under all glucose addition treatments.The above results suggested that the responses of nitrogen transformation in forest soils to continuous addition of dissolved carbon vary with forest soil fertility,with the response much more complex in the nutrient-poor forest soil than in the nutrient-rich one.