Dynamic Of Soil Nitrogen Mineralization In The Subtropoical Forest Of Cinnamomum Camphora And Pinus Massoniana

The soil nitrogen availability and mineralization have been studied by using resin-core technique in Cinnamomum camphora and Pinus massoniana ecosystem nearby Changsha city of Hunan province from July 2009 to April 2010, and the relationship between the aboveground carbon inputs and nitrogen mineralization has been researched also, the soil carbon input was controlled by removing and adding litter. The results are as follows:The seasonal contents of NH4+-N and NO3+-N in soil have significant difference (P<0.05) between the two forest types. The seasonal NH4+-N contents are the order as follow:July>October>January> April. The orders of seasonal NO3+-N content is that: October> July>January> April. The soil available nitrogen content between the two forest types have significant difference, and which in Pinus massoniana foresty are higher than in Cinnamomum camphora foresty. NH+4-N is the main existing forms of soil available nitrogen, which accounted for 89.88%～98.49% of soil inorganic nitrogen in Cinnamomum camphora foresty and 79.55%～95.89% in Pinus massoniana foresty.The net ammonifying quantity and nitrating quantity in each forest types are both have significant difference. The order of seasonal net ammonifying quantity is that: January> April>July>October, the seasonal nitrating quantity are the order as follows: July> October> April>January. The amounts of mineralization are remarkably different (P<0.05).Being incubated for 14days,28days and 42 days, the net soil nitrogen mineralization quantities have extremely significant difference between the two forest types, each of which is -33·82 (±3.48) mg·kg-1,-16.81 (±5.90) mg·kg-1 and 29.14 (±4.41) mg·kg-1 in Cinnamomum camphora foresty, and -59.93 (±3.48) mg·kg-1,-33.17 mg·kg-1 and -13.11 mg·kg-1 in Pinus massoniana foresty.The average tempreture (5cm) and humidity have great effect on nitrogen mineralization rate. The effect of soil tempreture in Cinnamomum camphora foresty is more obvious than in Pinus massoniana foresty. The net nitrogen mineralization quantities achive the peak when soil water content is 0.31 m3·m-3. There is extremely significant linear relationship between nitrification rate and ammonification rate.