| Soil fauna is an integral part of Earth’s terrestrial ecosystems and has a key role in ecosystem cycles.There are relatively few studies on the relationship between soil faunal community structure during apoplastic decomposition and the functional performance of decomposers in the decomposition system.In this study,we selected four typical forest types in Baotianman Nature Reserve and investigated the small and medium-sized soil fauna in the decomposition process of apoplankton in different forest types,analyzed the structural characteristics of small and medium-sized soil fauna colonized in apoplankton in different seasons and decomposition stages,and studied the variation of small and medium-sized soil fauna structure influenced by environmental factors such as forest type and soil nutrients.We also quantified the decomposition function of the forest by measuring the activity of soil decomposition enzymes and the decomposition rate of dead sediment,and analyzed the relationship between the variation of the community structure of small and medium-sized soil fauna and the difference of forest decomposition system function.This study aims to improve the information base of the relationship between soil biodiversity and ecosystem function in Baotianman Reserve and provide guidance for material cycling and biodiversity conservation in the north-south transition forest ecosystem in the context of global change.Four representative forest types,namely,Huashan pine,Quercus acutus,cork oak and mixed forest,were set up between 900 and 1400 m above sea level,with three replicate stands of each type and eight in situ dead leaf decomposition experimental sites in each stand,for a total of 96 in situ decomposition experimental units.The decomposition bag method was used to collect fresh deciduous leaves of dominant tree species from each stand type and transplant them in different stands for in situ culture experiments from August 2021.The effect of small and medium-sized soil animals on the decomposition system was tested by controlling whether soil animals were allowed to enter the decomposition bags through different pore sizes,i.e.,small mesh decomposition bags to isolate small and medium-sized soil animals,and large mesh decomposition bags to not isolate small and medium-sized soil animals.Since there is a freezing period of 3～4 months in Baotian Mann during winter,during which soil fauna are dormant,three typical periods of active decomposition were selected for sampling in November 2021(late autumn),April 2022(early spring)and September2022(late summer/early autumn),and small and medium soil fauna were separated from the soil inside and below the decomposition bags using the dry funnel method,and they were classified and identified to The functional taxa were classified and identified to "order"-based groups,and soil physicochemical,decomposition enzyme activities and decomposition of apoplastic matter were also measured.The main conclusions were as follows:1.A total of 8842 small and medium-sized soil animals were counted,belonging to 24 taxa.Among them,the dominant species were Ticks and Elasmobranchs,accounting for 85.55% of the total number;common species were Diptera,Diptera larvae,Hymenoptera and syntypes,accounting for 12.33% of the total number;12orders were found in rare taxa,accounting for 2.12% of the total number.2.In terms of the effect of seasonal changes on the faunal community,the number of individuals and taxa of small and medium-sized soil fauna were: late summer and early autumn > early spring > late autumn.In terms of vertical stratification structure,the number of small and medium-sized soil fauna was much larger in the apoplastic layer than in the soil layer.3.The degree of variation in the diversity indices of small soil fauna varied among sites in the apoplastic and soil layers,with the Shannon-Wiener diversity index(range 0.08-0.16)being less variable and the Pielou evenness index(range 0.25-0.48)and Simpson dominance index(range 0.01-0.32)were more variable.4.After one year of natural decomposition,the degradation rate of apoplastic leaves by small and medium-sized soil animals was as follows: cork oak forest(32%)> mixed forest(30%)> coniferous forest(28.5%)> broad-leaved forest(28%).The effect of soil fauna on the degradation of apoplastic leaves also differed from season to season: late summer and early autumn > early spring > late autumn.5.As degradation proceeded,ammoniacal nitrogen and total nitrogen contents showed a trend of decreasing followed by increasing in different forest types;total phosphorus contents showed a trend of increasing followed by decreasing.The non-metric multidimensional scale analysis(NMDS)of Baotian Man’s small and medium-sized soil fauna with soil physicochemical factors showed that the largest correlation between total soil nitrogen and total phosphorus and the major taxa of small and medium-sized soil fauna was dinoflagellates.6.The carbonase activity showed an increasing trend with the degradation level.The results of canonical correspondence analysis(CCA)and redundancy analysis(RDA)of the main taxa of small and medium-sized soil fauna from Baotian Mann with soil enzyme activities showed that the most influential taxa of small and medium-sized soil fauna(elasmobranchs and ticks)with the highest abundance were urease.In general,Baotianum small and medium-sized soil animals were able to participate in the regulation of enzyme activities related to carbon,nitrogen and phosphorus turnover in the forest decomposition system,which in turn influenced the decomposition of forest apoplankton.The higher the degree of apoplastic leaf degradation,the higher the activity of carbonases.Therefore,the degree of degradation of apoplastic leaves by soil animals can be inferred from the carbonase activity. |
