Seasonal Dynamics Of Small And Medium-sized Soil Fauna Communities Under Three Alpine Stands In Western Sichuan

The structure and function of soil animal community play a very important and irreplaceable role in the process of material cycle and energy transformation of ecosystem.The alpine forest in western Sichuan is located in the eastern edge of the Qinghai-Tibet Plateau and the upper reaches of the Yangtze River.It plays a very important and irreplaceable role in many aspects,such as soil and water conservation,biodiversity protection,global carbon cycle,regulation of regional climate and so on.But so far,the research on the effect of seasonal dynamic changes on the structure and function of soil animal community has not been reported,and there is a lack of research reports on the process of subalpine forest ecosystem from long-term dynamics.Therefore,in this study,typical coniferous forests in alpine and alpine areas of western Sichuan(purple fruit spruce:Picea purpurea),coniferous and broad-leaved mixed forest(Betula albosinensis + Abies faxoniana + Picea purpurea))and broad-leaved forest(alpine willow: Tilia tuan + Padus racemose + Salix paraplesia)were used as research objects,and the dry funnel method was used to study the characteristics of soil animal community in the past two years.It has a certain scientific significance for in-depth understanding of the relevant ecological processes driven by soil animals in subalpine forests and their seasonal relationships.The conclusions of the preliminary study are as follows:In this study,a total of 1955 soil animals were obtained,including coniferous forest,broad-leaved forest and mixed forest,belonging to 17 orders and 37 families.The dominant groups are Acaridae of Acarina,Acanthaceae and Isochronomidae accounting for61.07% of the total number of individuals,respectively.There are 27 groups in the coniferous forest,among which the dominant groups are Acaridae,Echinaceae and Echinaceae,accounting for 23.54%,25.00% and 23.54% of the total individuals,respectively.There are 32 groups in the broad-leaved forest,of which there are 4 dominant groups,which are Acaridae,Acaridae,Acanthidae and Echinaceae,respectively,accounting for 62.17% of the total number of individuals.In the mixed forest,there are 35 groups,of which the dominant groups are also Ichidae,Echinaceae and Echinaceae,accounting for 59.48% of the total number of individuals.In terms of vertical distribution,soil animals are mainly concentrated in litter layer,in which the number of litter layer in mixed forest is the most,followed by coniferous forest and broad-leaved forest.The number of soil animals in litter layer of all stands was significantly different from that in0-5cm soil layer and 5-10 cm soil layer(P < 0.05).The average number of individuals and groups of soil animals that can be detected is the highest in the growing season and the lowest in the freeze-thaw period.Although there are still a considerable number and groups of soil animals in each forest soil during the seasonal freeze-thaw period,soil freezing and freeze-thaw cycles significantly affect the number of individuals and groups of soil animals that can be detected.The peak number of soil animal groups in coniferous forest appeared in T6(November).It can be seen that seasonal freezing and thawing also has an effect on soil animal species.In the selected forest community,(Acarina)and(Collembola)were the dominant groups.The individual density and group number of soil animals in the litter layer of each community were significantly higher than those in the soil layer,and the highest in the growing season.Under different soil layers,soil animals showed vertical distribution,the litter layer was the most,the 0-5cm soil layer was the second,and the 5-10 cm soil layer was the least.In terms of the same functional group,the number of soil animals in the three stands was as follows:saprophytic > phytophagous > predator > omnivorous.Herbivore > saprophytic >predator > omnivorous in coniferous forest,saprophytic > herbivorous > omnivorous in broad-leaved forest and mixed forest.There were significant differences in soil animal shannon-wienner index and simpson index among the three stands(P < 0.05),but there was no significant difference in pielou index.The Shannon-Wiener index,Pielou index and Simpson index of the three forest communities were also significantly affected by seasonal changes.The Shannon-Wiener index and Pielou index of soil animals were the highest in the growing season and the lowest in the freeze-thaw period.The Jaccard index of the three stands was moderately similar,but the dynamics of the seasons are different.The Jaccard index at T1,T2,T3,T5 and T6 was small,indicating that the soil animal community structure of the three stands was quite different,while the Jaccard index of the three stands at T4 and T7 was higher and reached a moderately similar state.The comprehensive analysis shows that the soil animal community of alpine forest in western Sichuan has obvious seasonal dynamic characteristics.The Shannon-Wiener index and Pielou index of soil animals were the highest in the growing season and the lowest in the freeze-thaw period.There is an obvious freeze-thaw phenomenon in the soil animal diversity of mixed forest and coniferous forest,indicating that there is still rich soil animal diversity in the forest soil in cold winter.Mixed forest greatly increased the number of individuals and groups of soil animals in the forest,and the peak number of soil animal groups in coniferous forest appeared in T6(November).It can be seen that seasonal freezing and thawing also has an effect on soil animal species.The diversity of soil animals and the number of individual groups appeared "surface aggregation" in the soil layer,and the soil animals in the litter layer were significantly higher than those in other soil layers,and formed a vertical distribution structure in which the soil animal diversity decreased with the increase of soil layer thickness.On the one hand,these results prove the sensitivity of soil animal community to environmental changes,on the other hand,it also shows that soil freeze-thaw cycle,litter input and seasonal temperature drop have a strong impact on soil animal community structure.Maintaining the diversity and reproducibility of ecological species is the most basic embodiment of sustainable development.As an integral part of species diversity,soil animal diversity can be carried out by building mixed forests,strengthening coniferous and broad-leaved mixed forest and other ways to change the stand structure,and maintain the health and vitality of the forest ecosystem through scientific management and rational management of current and potential forest ecosystems.Maintain biodiversity and its ecological processes,so as to meet the needs of social and economic development for forest products and their environmental services,and then achieve sustainable forest management.