| secondary forests of Pinus massoniana, Acacia confusa in the back mountain of Fujian Agriculture and Forestry University were analyzed, including litter amount, component, seasonal dynamics,nutrient content and return,decomposition and the effect of litters respiration on soil respiration,in order to reveal the laws of the material cycle of ecosystems, to provide a theoretical basis for the maintenance of soil fertility and forest productivity and to find out carbon cycle characteristics of subtropical forest ecosystem.The results indicated as follows:1)The litter amount in the year of pinus massoniana forest,acacia confusa forest, secondary mixed forests of Pinus massoniana,Acacia confusa in sunny slope, secondary mixed forests of Pinus massoniana,Acacia confusa in shady slope were: 4583.76kg·hm-2,4958.65kg·hm-2,5567.44kg·hm-2,8111.04kg·hm-2,the litter amount difered in four forests, but leaf hold the absolute content,more than 55%. The litter amount in mixed forests is higher than that in pure forests, and the amount of different organs were in the sequence of leaf>branch>miscellany. Forests on the changing patterns of the total litter and organs litter in the same model, were all two peaks patterns.2) The nutrient content of various components(leaf,branch,bark and miscellany ) of pinus massoniana forest were in sequence of C>Ca>N>K>Mg>P,and reproductive organs was C>N>K>Ca>Mg>P.The nutrient content of various components of acacia confusa forest were in sequence of C>N>Ca>K>Mg>P. The nutrient content of leaf and branch of secondary mixed forests of Pinus massoniana,Acacia confusa in sunny slope were in sequence of C>N>Ca>K>Mg>P,bark and miscellany were C>Ca>N>K>Mg>P,and reproductive organs were C>N>K>Ca>Mg>P. The nutrient content of leaf,branch,reproductive organs and miscellany of secondary mixed forests of Pinus massoniana,Acacia confusa in shady slope were in sequence of C>N>Ca>K>Mg>P,and bark was C>Ca>N>K>Mg>P.3) The litter dynamic was studied using BP neural network and LS-SVM,to reveal the relation between litter and temperature, precipitation and evaporation firstly.The use of BP nd the results showed that the accuracy of the mean simulative errors of the two models for different forests were satisfactory,which were 8.32%,5.77%,4.92%,7.40% and 0.11%,0.09%,0.10%,0.12%,respectively. Further, the performance of LS-SVM better. 4) The annual total amount in litter returning to soil can be ranked in a decreasing order as secondary mixed forests of Pinus massoniana,Acacia confusa in sunny slope >secondary mixed forests of Pinusmassoniana,Acacia confusa in shady slope> acacia confusa forest> pinus massoniana forest, with different contents of 6 kinds elements.The nutrient return content of C were in sequence of secondary mixed forests of Pinusmassoniana,Acacia confusa in shady slope>secondary mixed forests of Pinus massoniana,Acacia confusa in sunny slope> pinus massoniana forest> acacia confusa forest, N were acacia confusa forest>secondary mixed forests of Pinusmassoniana,Acacia confusa in shady slope>secondary mixed forests of Pinus massoniana,Acacia confusa in sunny slope> pinus massoniana forest,P,K were secondary mixed forests of Pinusmassoniana,Acacia confusa in shady slope>secondary mixed forests of Pinus massoniana,Acacia confusa in sunny slope> acacia confusa forest>pinus massoniana forest,and Ca,Mg were secondary mixed forests of Pinusmassoniana,Acacia confusa in shady slope> acacia confusa forest >secondary mixed forests of Pinus massoniana,Acacia confusa in sunny slope>pinus massoniana forest.5)The amounts of six nutrients in litter of pinus massoniana forest returning to soil can be ranked in a decreasing order C >Ca>N>K> Mg >P,and acacia confusa forest,secondary mixed forests of Pinusmassoniana,Acacia confusa in shady slope and secondary mixed forests of Pinus massoniana,Acacia confusa in sunny slope were C>N>Ca>K>Mg>P.The amounts of C were 2454.55～4338.02 kg·hm-2,N variation range was 29.47～115.92 kg·hm-2,P was 1.06～2.58 kg·hm-2, K was 16.58～39.47kg·hm-2, Ca was 31.81～53.80 kg·hm-2,and Mg was 2.08～4.36 kg·hm-2.The amounts of six nutrients in components of pinus massoniana forest returning to soil can be ranked in a decreasing order leaf>branch>miscellany>bark>reproductive organs,of acacia confusa forest be leaf>branch>miscellany>reproductive organs,and of secondary mixed forests of Pinus massoniana,Acacia confusa in sunny slope and secondary mixed forests of Pinusmassoniana,Acacia confusa in shady slope be leaf>branch>miscellany>reproductive organs>bark.6) The total nutrients amounts of pinus massoniana forest,acacia confusa forest, secondary mixed forests of Pinus massoniana,Acacia confusa in sunny slope, secondary mixed forests of Pinus massoniana,Acacia confusa in shady slope returning to soil varied greatly with different months. There are two modes: double peak and three-peak type,and the high peak was in August, September and May,July next year. The components with the six elements on the nutrient return of the dynamic ranges with different patterns, there are three modes:single peak, double peak and three-peak type,and the high peak was different in different forests and components.7) The residual ratio of leaf can be summarized as follows: pinus massoniana forest((52.07%),acacia confusa forest(13.09%), mixed forests of Pinus massoniana,Acacia confusa(25%); of branch can be summarized as follows: pinus massoniana forest((74.9%), acacia confusa forest(54.2%), mixed forests of Pinus massoniana,Acacia confusa(69.89%). The decomposition ratio of litter can be ranked in a decreasing order as acacia confusa leaf> mixed leaf of Pinus massoniana,Acacia confusa> pinus massoniana leaf> acacia confusa branch> mixed branch of Pinus massoniana,Acacia confusa> pinus massoniana branch.The time of decomposing 50% and 95% of acacia confusa leaf was shortest,which is 0.4041a and 1.7463a,while the time of pinus massoniana branch was longest,which was 2.6517 a and 11.4603a.8) The concentration of nutrient elements in the process of decomposition were complicated. Organic C content fluctuated with the time,and on the whole gradually declined; N and P content in leave and branch enriched to some extent; K content had the same changes tendency, which always descreased with the time; Ca and Mg content was not very stable. The residual ratio of elements in litters were complicated, the law was not clear, and various elements in the course of the release enriched to some extent.9) The soil respiration rate under the cover of litters can be summaried as follows: pinus massoniana leaf range was 2.72～12.18μmol·m-2·s-1 ,acacia confusa leaf 2.9～10.52μmol·m-2·s-1, mixed leaf of Pinus massoniana,Acacia confusa 1.97～8.81μmol·m-2·s-1,pinus massoniana branch 2.51～8.11μmol·m-2·s-1, acacia confusa branch 2.14～7.58μmol·m-2·s-1, mixed branch of Pinus massoniana,Acacia confusa 2.95～12.09μmol·m-2·s-1,while the soil respiration rate without litters was 1.83～6.93μmol·m-2·s-1.All soil respiration rate showed a single peak curve, and basically season changes law was the same, of which the maximum appears in August or September, the minimum in the winter.10) The soil respiration rate under the cover of litters was significantly higher than that without litters. The soil respiration rate can be ranked in a decreasing order mixed branch of Pinus massoniana,Acacia confusa> pinus massoniana leaf> acacia confusa leaf> pinus massoniana branch> mixed leaf of Pinus massoniana,Acacia confusa> acacia confusa branch>the control,so the respiration rate of litters followed the sequence : mixed branch of Pinus massoniana,Acacia confusa> pinus massoniana leaf> acacia confusa leaf> pinus massoniana branch> mixed leaf of Pinus massoniana,Acacia confusa> acacia confusa branch. The contribution of litters respiration to soil respiration was 14.57～47.45 %; litter respiration rate was higher in summer and autumn, lower in winter.
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