| In order to elucidate the mechanism of soil animal food webs to warming in midhigh latitude wetlands,the permafrost region,the Greater Khingan Mountains,was selected as the research area in this study.Microorganisms and arthropods were investigated as the research objects.The structural equation model(SEM)was used to integrate environmental factors,soil physical and chemical properties and soil animal taxa densities in different trophic level.Feeding habits were also included to reveal the mechanism of the warming effect on the soil animal food web.The results are as follows:(1)Response characteristics of soil biodiversity to warming in middle and high latitude wetlandsIn this study,12 phyla and 228 orders of microorganisms,3015 Collembola belonged to 28 species and 5877 mites belonged to 30 species were obtained.At the level of microbial phyla,the abundance of Acidobacteriota and Proteobacteria in the soil of typical peat wetland ecosystems accounted for more than 90%,and they were at the absolute dominant phylum level in the phylogenetic tree.Warming significantly changed the fungal species composition in peat wetlands with seasonal variations.Warming increased Collembola densities in permafrost wetlands(roughly an 8-fold increase in April),and the warming effect was most pronounced at colder seasons.Warming had no significant effect on mites,indicating that warming had obvious group-specific effects on soil animals.(2)Determination of soil animal stable isotope preservation conditions and improvement of accuracyThrough the 12-month continuous monitoring of δ13C values of two laboratorygrown collembola,we found that ethanol(100%)preservation methods and storage temperatures(room temperature and 4℃ in fridge)did not affect the δ13C value.For soil microarthropods,DNA sequencing could be combined with stable isotope analysis to analyze feeding habits(both storage concentrations are 100%).The practical combination of feeding habits and identification accuracy of soil fauna could be further expanded.Realize nmol level C and N stable isotope test by developing Nano EA system.The CN stable isotope test of the rare groups of soil microarthropods was available,and the determination of the feeding habits of the rare groups of similar soil animals and small biomass groups becomes possible.The accuracy of the total group of soil animal food web was further improved.(3)Response mechanisms of soil animal food web to warming in mid-high latitude wetlandsIn general,this study carried out stable isotope tests on soil animals in different sample collection periods(April,May,August,September and October)under warming treatment.Feeding characteristics and trophic level characteristics of soil fauna were also analyzed.The overall food web structure was similar to previous results in grass and forest ecosystems.Including herbivorous taxa(Coleoptera larvae,etc.),decomposing taxa(some Oribatida,Collembola,Diptera larvae,Pillworm),secondary predatory taxa(including ants,crab spiders,etc.)and top predatory taxa(spider,centipede etc.).It showed that the improved isotope method not only ensured less sample amount,but also retained high accuracy for testing stable isotope values of soil fauna.The δ13C value of soil animals showed a certain seasonality,increasing from April to August and decreasing from September to October,while the δ15N did not fluctuate much.At different sampling seasons,the effects of warming on the soil animal food web were also different.In April,warming treatment(especially in low temperature season)could increase the trophic level of soil animals.While the warming effect in spring or summer disappeared when the temperature was increasing.It was indicated that warming increased the development of soil fauna and their food resources,but did not maintain this trend indefinitely.Stable isotope-labelling experiments further showed that different soil animal groups have different feeding ways derived from roots and litter resources,and predatory groups can obtain energy from both roots and litter resources at the same time to maintain their own survival.Further analysis by structural equation model confirmed that warming affected the entire trophic composition of soil animals through climate factors,soil carbon and nitrogen content.In summary,warming in wetlands at middle-high latitudes could significantly change the composition of soil microorganisms and increase the number of soil Collembola,mainly through the increasing amount of food resources in this area.With the increasing food resources and soil mesofauna,warming could increase the length of soil animal trophic level through bottom-up regulation.This study could help to comprehensively disclose the mechanism of the impact of warming on soil organisms from the perspective of microorganisms,soil animal decomposition groups,omnivores and predators,and provided the necessary data basis for predicting the overall impact of future climate change conditions on soil organisms in sensitive regions. |
