| The litter decomposition plays a critical role in regulating the buildup of the forest soilorganic matter, releasing of nutrients for plant growth, and influencing the carbon cycling.Soil fauna play an important role in litter decomposition processes through breakdown oflitter, digestion and stimulation of microbial activities. A litter decomposition experiment wasconducted in a Pinus koraiensis mixed broad-leaved forest, which is one of the typical forestvegetation types in the Changbai Mountains (42°24′N,128°05′E), located in northeasternChina. The four most abundant tree specie litters in study site (Pinus koraiensis, Fraxinusmandshurica, Tilia amurensis and Acer mono) were used by litterbags, including4mm,2mmand0.01mm in order to control the different body size of soil fauna exiting or entering, tostudy the decomposition and nutrient release of the monoculture and mixed litters. FromOctober2009to October2011, litter samples were carefully retrieved from the field tolaboratory on the26th of each of the four months of April, June, August, and October. Basedon the data of decay rate, dynamics of the C, N, P, Ca, Mg and Mn of litter and soil faunacommunity, the combination of variance analysis, multivariate analysis, rarefaction andmultiple regressions were used to analyze the dynamics of litter decomposition process,nutrient release, and soil fauna community, to establish the relationship between the soil faunaand litter decomposition，and to explore the role of different soil fauna groups in litterdecomposition and nutrient releasing. The main results are summarized as follows:(1) During the2years study period, the litter decay rate had seasonal dynamics with theseasonal fluctuation of temperature and moisture. The loss rate of litter in summer andautumn were higher than that in winter and spring. The four different litter speciesdecomposed in monoculture at different rates, ranging from almost60%mass loss for litter ofP. koraiensis to almost complete mass loss for F. mandshurica after two-year of incubation.Three broadleaf leaf litters mixed with pine litter had idiosyncratic effects on the totaldecomposition rates, and the direction of these effects varied with the feld incubation timeand composition species. At the early stage of decomposition, all litter mixing treatmentsshowed that the remaining litter mass was signifcantly higher than that of the predictedvalues, indicating that the litter mixing retarded the decomposition. However, the signifcanceof this difference disappeared in the later phases of the study period, with the exception ofP.koraiensis+T.amurensis, indicating that the litter mixing had not brought positive effects tolitter decomposition.(2) Repeated measures ANOVA showed that litter treatments, field incubation time andtheir interaction had a significant impact on the rate of elements releasing. For N and P, alllitter treatments had an obvious enrichment process in the first year. While in the second year,the absolute content of the elements in each litter treatments gradually reduced except forP.koraiensis. For the Ca, the P.koraiensisthe in4mm and2mm litterbags also hadenrichments process; those in the other three kinds of litter gradually reduced with decomposition. For C and Mg, they reduced with decomposition in all kinds of litter. Mnelement content also reduced with decomposition in addition to F.mandshrica litter. Thechanges of cellulose content in all litters were fluctuated, while lignin content increasedduring the experiment. By comparing the observed values of each element releasing rate withthat of predicted values, it showed that the mixture of litter had different effects on differentelements releasing. For C releasing, the direction of effects varied with field incubation time.For N element, the mixed litter promoted the rate of releasing, but it was mainly manifested inthe first year of decomposition. For P element, it had idiosyncratic effects on the release rate,and the direction of these effects varied with the field incubation time and compositionspecies. For Ca, Mg and Mn elements, it had a certain inhibitory effects, with exception of theP.koraiensis+F.mandshurica+T.amurensis+A.mono for Ca release rate.(3)42groups of soil fauna were obtained in litterbags during the2years study period.The most abundance taxa were Acarina, Collembola Enchytraeidae and Diptera (larvae).Rarefaction curves showed that the species richness was signifcantly different among the fourmonoculture litters. F. mandshurica showed the highest richness of soil fauna, while P.koraiensis showed the lowest. The PCA results showed that the composition of the soil faunacommunities varied among the four monoculture litter species during the decompositionperiod. By PCA, rarefaction and variance analysis, the litter mixture treatments did notsupport more species richness of soil fauna than the components of monoculture litter. Theindependent t-tests showed that the litter mixing did not promote the total density of richness,abundance and diversity of soil fauna (relative to the predicted values).(4) Soil fauna had great contribution to litter decomposition, and also had greatinfluences on the element cycle in ecosystems. There were significant positive relationshipsbetween individual and group’s density of soil fauna and litter decay rate. Throughout theexperimental period, litter species, field incubation time, mesh size and they interaction had asignificant impact on the litter decomposition rate (P<0.05). Contribution rate of soil fauna toF. mandshurica litter decomposition was great,16.87%; less to T. amurensis litterdecomposition,2.77%after two-year study period. The main groups of soil fauna individualdensity (Acarina, Collembola, Enchytraeidae and Diptera (larvae) and total soil fauna densityhad signifcantly positive relative to releasing of C, N, Ca and Mg, while had weak relative toP and Mn elements. The Contribution of different group soil fauna (macrofauna,meso-microfauna) to litter decomposition and nutrient elements releasing were varied amonglitter treatments. In addition, the soil fauna accelerated to litter decomposition and nutrientelements releasing mainly manifested in the second year of the decomposition experiment. |
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