Study On Dynamics Of Litter Nutrient Return, Retranslocation And Decomposition Of Eucalyptus Grandis Plantation

Litter is major material pool of forest organic and the base of maintain the soil nutrient, and the major course of the material cycling and energy flow in forest ecosystem. It is very important for the nutrient to return to soil through litter to remain the sustainable productivity of the forest. Now, the Eucalyptus plantation is one of most tree species planted in south of our country. It is vital significance to plant and manage the Eucalyptus plantation through research the characteristic of litter to thoroughly understand the structure and the function of the forest ecosystem. From July 2004,the experiment choose the Eucalyptus grandis plantation planted in 1997 in YongYa SiChuan province, study on the litter production, nutrient return, nutrient retranslocation, litter decomposition and the soil nutrient change in a growth cycle, the result showed:(1) The annual litter production of four Eucalyptus grandis plantation were 8786 , 8112 , 5590, 6011 kg/hm² respectively, the annual litter production was connected with the forest density, leaf production was increased with the increase of the standing density, branches and barks had no remarkable relation with the density. The components of litter production was leaf> branches > barks. There was a peak and valley in the whole year, highest in May and lowest in January. The litter production of seasonal variation tendency in sequence of spring > summer > autumn > winter. Leaf mainly fell in spring while branches and barks fell main in summer.(2) The annual five macro-elements return to the soil through litter were 95. 32, 86.90, 67. 72, 66. 37 kg/hm² respectively, the sequence of nutrient return was N > K > Ca > Mg > P. E₃ was the highest in N potential return and E₁ E₂ E₄ were close, the litter of E₃ had the higher effect to improve the soil which was the reason that the soil nutrient content of E₃ was higher. The sequence of nutrient return of litter components was: leaf> branches > barks. Leaf was the main components of the nutrient return. The dynamic of N, P, K, Ca, Mg return in four Eucalyptus grandis plantation were basically similar. The nutrient return was higher in spring and summer than in autumn and winter, lowest in January..(3) Before falling, most of N, P in leaf and branches were transferred physiologically, while K, Ca, Mg transferred direction was uncertain, sometimes was positive and sometimes was negative. The transfer efficiency of P was the highest, reached 60.6% in leaf and 70.1...