| Soil fauna is an important component in forest soil ecological system, and the community structure and composition of soil fauna have significant effect on soil formation, material cycling and energy flowing. Pinus massoniana is the main species of middle and upper reaches of Yangtze River forest, and have strong endurance capacity for dry and barren soil. However, a series of ecological problems we also found. For its single structure, Pinus massoniana plantation is characterized by low productivity, low biodiversity, soil degradation, pest frequently-occurring and so on, which seriously hinder the ecological, economic and social development. Reconstruction of low yield plantation forest by artificially felling to form the forest gap is an effective way to improve the ecological service function and achieve the sustainable management. In this paper, the composition, dominant species, seasonal dynamics, profile distribution and ecological characteristics of soil animal in Pinus massoniana plantation were studied in seven gaps different size of (G1:100 m~2, G2:225 m~2, G3:400 m~2, G4:625 m~2, G5:900 m~2, G6:1225 m~2, G7:1600 m~2) in the middle and upper reaches of Yangtze River, and the diversity characteristics and functional groups were studied. In the present study, hand picking up method, Tullgren method as well as Baermann methods were used to collecting macro, meso and micro-soil fauna respectively. The results showed as below:(1) A total of 33 859 individuals of soil fauna were collected, belonging to 6 phyla,14 classes,35 orders and 265 families (Attached list 1), in January, April, July and October of 2015. Among them,29 502 individuals were collected in seven sized forest gap, and 4 357 individuals in the contrastive under forest. The dominant species is Nematoda, accounted for 81.07% of the total. The frequent species are Enchytraeidae, nothrid mites, Isotomidae, and oribatulid mites, accounted for 10.77% of the total. The rest 260 groups, such as Sejidae, oppioid mites, Diptera larvae, Formicidae etc., belong to rare group, accounted for 8.16% of the total.(2) With the increase of the gap area, the average density of soil fauna decreased gradually, but when the area of gap is more than 900 m~2, the average density increased and reached the maximum, in the G5-G7 (900-1600 m~2) plots the average density of soil fauna again fell with the increase of forest gap. The groups number of soil fauna is increasing with the raise of forest gap, and in G5 (900 m~2) plots reached the maximum, then gradually decreased; the order of soil fauna average density is:G5(6.41×105)> G6(3.87×105) G1(1.77×105)> G7(1.76×105)> G2(1.69×105)> G3(1.49×105)> CK (1.21×105)> G4 (0.90×105), rank of groups number is:G5(157)> G2(138)>G4(136)> G3(135)> G7(131)> G6(130)> G1(127)> CK(121); The seasonal dynamic of soil fauna average density in each forest gap reached the maximum in October, minimum in January, and middle in April or July. Nevertheless, the maximum group number showed in April, minimum in January, and middle in July or October.(3) The average density and groups number of macro fauna were gradually increased with the forest gap increased, and reached the maximum in the G4-G5 (625-900 m~2)in any season, then gradually reduced with the increase of forest gap. Although the density distribution of meso-micro soil fauna is relatively complex, we founded generally dense in larger forest gap, the maximum was at G5-G6 (900-1225 m~2) plots. There was no huge fluctuation in group number distribution of meso-micro soil fauna, but it generally was similar to the distribution of macro fauna, and the maximum was at G4-G6 (625-1225 m~2) sample plots.(4) The average density and groups of soil fauna in Pinus massoniana plantation forests gap obviously decreased with the increase of sampling depth in different season, except in January. An unusual phenomenon was showed that the number of groups in parts of litter layer appeared to be lower than those of the 0-5 cm soil layer. The average density of soil fauna were aggregate in the upper soil layer obviously, and in litter layers were lower than those of the 0-5 cm soil layer in each season.(5) The feeding habit were mainly omnivorus, accounting for over 60 percent of the total individuals. Saprophagous, phytophagous and mycophagous soil fauna followed in different size of Pinus massoniana plantation forest gap, and in larger gap omnivorous soil fauna was significantly higher than that of small and medium sized gap. The saprophagous, predatory, omnivorous and herbivorous animals occupy more than 90 percent of the total taxa, and the saprophagous animals were the main, accounting for more than 30 percent in several gaps; the percentage of saprophagous and predatory groups number decreased with the increase of forest gap. Later, the omnivorus density proportion in each gaps increased while groups number of the other feeding habits showed no significant difference.(6) The formation of gap reduced the Shannon-Wiener index and Margalef index of soil fauna in small or large size, but little influenced in medium forest gap, The Shannon-Wiener index and Margalef index distribution in each forest gap roughly showed the same trend, both increased in G1-G4 (100-625 m~2) plots, and reached the maximum value in G4 (625 m~2), decreased in G5 (900 m~2) plots and then increased again in G5-G7 (900-1600 m~2).Instead, the Simpson index is opposite, With increasing gap size, the Marglef index of soil fauna increased.(7) The study showed that the influence of gap size on the structure of soil faunal community diversity and characteristics (Shannon-Wiener diversity index not contained) was extremely significant diffrence (P< 0.01). Exception of the interaction between seasonal variation and the gap size had no significant influence on group number and Marglef index of soil fauna (P> 0.05), the rest were influenced significantly (P< 0.05). Correlation analysis showed that forest gap size and soil faunal communities composition and Density-Groups index was extremely different with positive correlation (P< 0.01); the Simpson index and Margalef index was different with positive correlation (P< 0.05); the Shannon-Wiener index is extremely different with negative correlation (P< 0.01), and the Pielou index is different with negative correlation relationship (P< 0.05).This study showed that the mid-size Pinus massoniana Plantation gap size (625-900 m~2) is beneficial to maintain the soil faunal abundance, individual richness and diversity. Therefore, we can construct medium-sized gaps to increase the richness of soil fauna, maintain the underground diversity and stability of Pinus massoniana plantation ecosystem. However, this research put forward a low yield Pinus massoniana forest rebuilding solution that only in consideration of the soil faunal richness and diversity. We should also consider the interactions between plants, animals, and soil microorganisms in the practice of Pinus massoniana plantation management. |
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