| Litter decomposition plays an essential role in maintaining soil fertility in the forest. Soil fauna which affected by the type and quality of litter and the stage of decomposition are active participants during the decomposition of litter. Therefore, the research on dynamics of soil fauna community during litter decay can provide important scientific basis for the cultivation and the sustainable management of plantation. Eucalyptus(Eucalyptus grandis) is one of main afforestation tree species in the industrial raw material forest in the south, and alder (Alnus formosana) is a nonleguminous and evergreen tree species with the characteristic of fast growing and nitrogen-fixing. In order to maximum extently avoid the ecological problems, such as soil fertility and biodiversity decline, the litter mixed experiment of Eucalyptus grandis and Alnus formosana was conducted. The corresponding problems were put up:(1) How do control the ratio of eucalyptus litter weight to alder litter weight to maintain productivity and biodiversity in the mixed forest?(2) Will different tree species mixture affect the litter decomposition process?(3) Will different tree species mixture change dynamitic of soil fauna community? All those are lack of corresponding research. Decomposition characteristic and dynamic of soil fauna in different ratio mixed litters (Tâ… :eucalyptus10g, alder Og; Tâ…¡:eucalyptus7g, alder3g; Tâ…¢:eucalyptus5g, alder5g; Tâ…£:eucalyptus3g, alder7g; Tâ…¤:eucalyptus Og, alder10g) were investigated with the method of litterbags in Suji town, Leshan city, Sichuan province. The aim was to explore the effect brought by mixture of eucalyptus and alder on decomposition rate, dynamics of nutrient and soil fauna community structure and provide the support of science and technology for the building of reasonable and feasible plantation.(1) The dominant groups were Collembola and Acariformes which belong to meso and microfauna. The common group was Opithopora which belongs to macrofauna in different ratio mixed litter. Compared with TI litter, the macrofauna preferred to live in TV litter. The individual numbers of macrofauna in mixed litter were between TV litter and TI litter. The individual numbers of macrofauna increases with quantity of the alder added. Compared with TV litter, the meso and microfauna preferred to live in TI litter. The individual numbers of Psocoptera reached highest in TV litter and Opithopora in mixed litter. Collembola and Pauropoda preferred living in TI litter. All these suggested: the community structure of soil fauna would change when alder was added in Eucalyptus.(2) The individual numbers of soil fauna in6-mesh litterbags were TI>TII>TIII>TIV>TV, and those of macrofauna were TIII>TIV>TV>TII>TI and meso and microfauna were Tâ… >Tâ…¡>Tâ…¢>Tâ…£>Tâ…¤. The group numbers of macrofauna were maximum in TV litter and minimum in TI litter. The individual numbers of soil fauna in30-mesh litterbags were TI>TII> TV>TIV>TIII and in260-mesh litterbags were IV> Tâ…¢>Tâ…¡>Tâ… >Tâ…¤. The total individuals of soil fauna showed extremely significant difference in6-mesh litterbags, no significant difference in260-mesh litterbags and30-mesh litterbags among five different ratio mixed litter. The individual numbers of meso and micro fauna were260-mesh>30-mesh>6-mesh and there was significant difference between30-mesh and6-mesh litterbags. The individual numbers of meso and microfauna were more than those of marofauna in6-mesh litterbags. The group numbers were30-mesh>6-mesh>260-mesh and there was significant difference in30-mesh litterbags, extremely significant difference in6-mesh litterbags and no significant difference in260-mesh litterbags among five different ratio mixed litter. All these showed the mixture of eucalyptus and alder could increase the individuals of soil macrofauna, whereas no effect on the individuals and groups of meso and microfauna, compared with the eucalyptus litter.(3) The decomposition rate was TV>TIV>TIII>TII>TI in6-mesh litterbags, and the fast decomposition stage of TI was in August, Tâ…¡ and Tâ…¢ in July and TIV and TV in May. The decomposition rate of Tâ…¡ litter increased greatly due to the addition of alder in early stage, and the decomposition rate of TIV litter declined because of the eucalyptus added. Before October2009, the decomposition rate of TI litter was faster than that of Tâ…¤ litter in260-and30-mesh litterbags. Under near natural state (6-mesh), the ratio of Tâ…¡ could accelerate the decay of litter.(4) Background soil fauna included damp living meso and micro fauna, dry living meso and micro fauna and-macrofauna. The-dominant-group was Nematoda and the common groups were Rotatoria and Enchytraeidae among damp living meso and micro fauna. The dominant groups were Collembola and Acariformes among dry living meso-, micro fauna. The dominant groups were Opithopora, Isoptera, Coleoptera and Hymenoptera among macrofauna. There were more individuals in soil under TI plantation than mixed and TV plantation. The soil fauna, especially macrofauna, showed significant difference among different soil layer and more soil fauna happened in the top soil.(5) There was extremely significant difference in initial N, significant difference in initial Ca and Mg, and no significant difference in C, P and K among different ratio mixed litter. The ratio of C:N showed extremely significant difference between eucalyptus and alder. The elements concentration of different ratio mixed littler declined in6-mesh litterbags during decomposition. The elements of C, K declined slowly and Mg fast in TI litter. The elements of N, P declined slowly and C, Ca fast in TV litter. The element of N, C and Ca declined slowly in TV, TI litter respectively, P, Mg declined fast in TI litter in30-mesh litterbags. N and Mg declined fast in TI litter and slowly in TV litter in260-mesh litterbags. Mass loss rate was extremely significant positively correlated to the concentration of N, Ca, significant correlated to concentration of P, negatively correlate to the content of C, but there was no obvious difference.(6) The concentration of elements in260-mesh litterbags was higher than in30-mesh litterbags, that is to say, the nutrient release rate of litter in260-mesh litterbags was slower than in30-mesh litterbags, however, the individual numbers of soil fauna were higher in260-mesh litterbags than in-30-mesh litterbags and the group numbers were on the contrary. Different groups of soil fauna could stimulate the release of nutrient elements. The release rate of nutrient elements which was attribute to the soil macrofauna showed the order:Mg>P>K>N>Ca>C. Action of macrofauna to Mg was highest, achieving92.5%, however to C was lowest (32.05%), to N was highest in TI litter.All the research suggested that the mixture of Eucalyptus grandis and Alnus formosana could increase the numbers of individual and group of macrofauna, accelerate the litter decomposition and nutrient cycling compared with Eucalyptus.grandis. Therefore, it will accelerate the. cycle-of matter, improve the soil fertility and stimulate the growth of plant, when Alnus formosana is planted in the plantation of Eucalyptus grandis by the ratio of Tâ…¡. |
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