Study On Soil Faunal Communities And Functions During Litter Decomposition In Three Forest Types From Montane Region Of Eastern Liaoning Province, China

Account for 55% of the total forests are secondary forests in China, furthrermore, more than 60% of the forest types distributed in northeast China. However, driven by the increasing demand for timber, the area of larch plantations continues to expand in secondary ecosystem, and mosaic plantation/secondary forest landscapes have been formed. But these blind forest management have caused many problems, especially the soil degradation, and the obstacle of litter decomposition is one of the impartant reasons. Soil fauna is the dominant biotic factor affecting litter decomposition, it could regulate and control the processes of litter decomposition and nutrient release by directly consuming the decayed biological tissue, or indirectly influencing the community structures and stimulating bioactivity of the soil microorganisms. Research on the soil faunal communities structure and the function of soil fauna during litter decomposition, is the basis of reveal the mechanisms of soil degradation.The natural secondary forest, larch plantation, larch-broadleaved mixed forests were selected in this study. Soil faunal communities were investigated in these three forest types; by means of litterbag method, conducted the experiments of in sute decomposition and reciprocal decomposition of the broad-leaved litter, needle litter and mixed litter; clssified and counted the soil fauna during the litter decomposition.Using variance analysis, principal component analysis（PCA） and redundancy analysis（RDA）, analyzed the difference of soil fauna communities and the relationship between communities and environmental factors, and revealed the function of soil fauna in litter decomposition. The primary results are as follows:（1） Total of 102667 meso and micro-fauna were collected, belonged to 3 phyla, 10 classes, and 90 groups, Oribatida, Isotomidae, Neanuridae and Onychivridae were the dominant groups. Mesostigmata, Prostigmata, Tomoceridae, Tubificida, Entomobriyidae, Brachycera larvae and Nematocera larvae were common groups. The individual density of meso and micro-fauna ranged from 7.55×10³ ind·m^-2 to 6.45×10⁴ind·m^-2. On horizontal distribution, the individual density of soil meso and micro-fauna communities in larch plantation was the highest, on the vertical distribution, the communities had surface-aggregation. Repeated measures analysis of variance showed that, the season significantly effected on individual density, group numbers, diversity indexes, and the groups density of predatory, saprophagous and phytophagous rophic groups（P<0.05）; the layer significantly effected on individual density, group numbers, diversity indexes, and the groups density of saprophagous and phytophagous rophic groups（P<0.05）; forest type had a significant effect on group numbers and diversity indexes（P<0.05）. RDA showed that, the meso and micro-fauna communities in litter layer were significantly effected by litter p H and moisture（P<0.05）, and soil layer were effected by soil p H, soil moisture and soil organic matter content（P<0.05）.（2） Total of 4046 macro-fauna were collected, belonged to 3 phyla, 8 classes, 71 groups, total biomass was 454.32 g, Lumbricida, Tubificida and Geophilomorpha were the dominant groups. Agelenidae, Scarabaeoidea, Staphylinidae, Brachycera larvae, Polydesmida and Nematocera larvae were common groups. The individual density of macro fauna ranged from 30.37 ind·m^-2 to 164.44 ind·m^-2, the biomass density ranged from 2.29 g·m^-2 to 25.47 g·m^-2. Repeated measures analysis of variance showed that, the season significantly effected on individual densitys, group numbers, total biomass dendity, earworm density, diversity indexes, the groups density of predatory, saprophagous and phytophagous trophic groups（P<0.05）; the layer significantly effected on individual density, group numbers, total biomass dendity, earworm density, diversity indexes, the groups density of saprophagous trophic group（P<0.05）; forest type significantly effected on group numbers and diversity indexes（P<0.05）. RDA showed that, the macro-fauna communities in litter layer were significantly effected by litter moisture, depth, p H and total carbon content（P<0.05）, and soil layer were effected by total soil carbon content, total soil nitrogen content and soil organic matter content（P<0.05）.（3）At the end of the first year, the natural accumulate loss rate of broad-leaved litter, mixed litter and needle litter was 50.42%, 53.83% and 33.92%, respectively. The turnover time were 4.34⁸.88 years,3.92⁶.49 years and 8.61¹0.95 years, respectively, based on the Olson decay model. During the decomposition, the decomposition rate from midsummer to early fall was higher than that from early winter to late spring. The total carbon content was decreasing, which indicated the carbon element was releasing. The nitrogen and phosphorus content fluctuated obviously, which indicated they had obvious enrichment process during decomposition. The C/N remained decreasing.（4）During the first year, the soil fauna participated in litter decomposition main included Oribatida, Isotomidae, Mesostigmata, Onychivridae, Neanuridae, Tubificida, Tomoceridae, Nematocera larvae, Brachycera larvae and Entomobriyidae. The major functional group was saprophagy. PCA showed that the soil fauna communities of needle litter were different from the others, obviously, especially in August, and the difference main reflected on the individual density.（5） More specifically speaking, at the end of the first year decomposition in the field by litterbag method, the contribution rate of all soil fauna to broad-leaved litter, mixed litter and needle litter was 24.75%, 22.36% and 11.05%, respectively, of which the contribution rate of meso and micro-fauna was 17.35%, 14.85% and 7.80%, the contribution rate of macro-fauna was 7.40%, 7.51% and 3.25%. The functions of soil fauna in different litter decomposition were different, the same to the elements releasing. The contribution of meso and micro-fauna was higher than that of macro-fauna. The contribution of meso and micro-fauna to broad-leaved litter and mixed litter was higher than that of needle litter, and the effect increased then decreased generally. The effect of macro-fauna had no regularity. The contribution to the release of carbon was obvious, while the contribution to the release of the nitrogen and phosphorus was unobvious.