The Impact Of Soil Fauna On The Litter Decomposition In A Secondary Oak Forest And A Pine Plantation In Xiashu Experimental Site

The litter decomposition is one of the most important processes in the circulation of matter and energy in forests. The litter decomposition can release energy and nutrients, which were reused by the plants in order to make sure the circulation of matter and forests. Soil fauna plays an important role in this process, which is always ignored. Direct researches about this aspect are lake of, especially in the sub-tropical places. The following questions were considered in the present study: 1) What roles does soil fauna play in regulating litter decomposing rate? 2) How much are the roles? 3) How do litter nutrient releasing?In order to compare the decomposing function of soil fauna on the oak litter and coniferous litter, the study applies two methods to exclude the functions of different kinds of soil fauna in Xiashu Experimental Site in Jiangsu province, southern China: One is bags of different meshes, the other is naphthalene. Two plots (one dealt with naphthalene and the other without naphthalene) were set, each had four duplicates. Nine groups consisted of three mesh bags (1cm,1mm,0.3mm) were placed in each duplicate. Bags were collected once in two months. Soil fauna were separated and investigated after the bags were collected once two months. At the same time, left weight,nitrogen,phosphorus were measured.After one and half a year, the results indicate that:(1) Both in the secondary oak forest and pine plantation forest, the number and diversity of soil fauna in the sites dealt with the same methods (sites dealt with naphthalene and sites dealt without naphthalene) are bags with 1cm mesh size﹥bags with 1mm mesh size﹥bags with 0.3mm mesh size. The exclusion of soil fauna through different meshes is significant between bags of 1cm and bags with 1mm mesh size. Compare to the soil number in the 1㎝ mesh size bags, the exclusion of soil fauna in 0.3mm mesh size bags came to 70.00% in the two forests, while the exclusion of soil fauna in 1mm mesh size bags was about 34.00%.(2) Both in the secondary oak forest and pine plantation forest, the number and diversity of soil fauna in bags with the same mesh ( 1cm,1mm and 0.3mm) are bigger in the sites dealt without naphthalene than those in the sites dealt with naphthalene. The exclusion of soil fauna through naphthalene is especially significant between bags of 1cm and bags with 1mm mesh size. Contrast to the control plots, the average exclusion of soil fauna in the oak treat plots was61.48%, while the number in the pine plantation came to 88.06%.(3) Comparing the soil fauna number and diversity in the same plot, we can conclude that the soil fauna number in the plot dealt with naphthalene on the oak forest is 1.25 times of that on the pine plantation. While the soil fauna number in the plot dealt without naphthalene on the oak forest is 1.47 times of that on the pine plantation. Soil fauna number in the plot dealt with naphthalene on the oak forest is significant different with that on the pine plantation.(4) Until May, 2006,decomposing rates with three mesh size(1cm,1mm,0.3mm)in plots that were dealt with naphthalene were 27.48%,27.10%,26.35% in oak forest and 29.19%,21.09% and 19.59% in pine plantation, while in plots that were dealt without naphthalene were 30.97%,27.86%,27.48% in oak forest and 29.94%,28.81% and 27.18% . From the results we can conclude a same decomposing law in the oak forest and the pine plantation which were dealt with the same method : litter decomposing rates in the 1cm mesh size bags﹥litter decomposing rates in the 1mm mesh size bags﹥litter decomposing rates in the 0.3mm mesh size bags. And litter decomposing rates of bags with the same mesh in the same forest were bigger in the plots which were dealt without naphthalene than those in the plots which were dealt with naphthalene. All the differences are significant.(5) The contribution rates of the soil macro-and mesofauna to plant litter mass loss was about 40.07% in the secondary oak forest and 34.56% in the pine plantation. Comparing the decomposing rates of different forests in plots that were dealt with the same method, we can conclude that oak decomposing rates were bigger than the pine decomposing rates in plots dealt with the same method. The difference is significant.(6) Comparing the decomposing rates and the number and diversity of soil fauna, we can conclude that soil fauna number and diversity play an important role in the litter decomposing. Besides the soil fauna diversities in bags with 1mm mesh size were correlated with the litter decomposing rates in the pine plots that were dealt without naphthalene .(7) The nutrients are released during the decomposition. Because of the effects of the falling, contents of nitrogen and phosphorus declined quickly at the begging of the decomposition and reached the minimum at May in 2005,which declined 38.67% and 49.00% respectively in the oak forest and 48.85% and 44.82% in the pine plantation. From May in 2005, contents of nitrogen and phosphorus began to rise stably.The results indicate that soil fauna plays important roles in the litter decomposition. Moreover, in the north sub-tropical area, soil fauna might play more important roles in the litter decomposition process in oak forests than in the pine plantation. Our results provide theory basis for the further explanation of the effects and roles of soil fauna in the forest ecosystems.