Above ground Primary Productivity and Nutrient Cycling of Eucalyptus grandis ×E.urophylla Plantation

After the investigation on tree growth,tree biomass increment,tree nutrient accumulation,litter-fall and it′s decomposition,understorey biomass and nutrient accumulation,nutrient cycling of E.grandis × E.urophylla plantation from 1.5 to 3.5 years old,it is found that the highest growing period of tree diameter and biomass of the plantation was 2 years old, and they were slowing down at 3 years old.Tree biomass of 1.5,2.5 and 3.5 years old plantations were 14.5,28.5 and 38.0 t/hm2 respectively,and the understorey biomass were 2.6,3.4 and 6.3 t/hm2 respectively.Nutrient accumulation by understorey was about 20%～40% of total above ground nutrient accumulation.Annual litter-fall was 5.6 t/hm2. Litter decomposition rate was 55% per year and most nutrient content in litter-fall was lost to soil in a year.This plantation established nutrient cycling system earlier than the others. N fertilization had improved N accumulation and cycling rate obviously.If there is some P fertilization,trees would grow better.