Community Assembly Of Isotomidae (Collembola) Along An Elevational Gradient In The Changbai Mountains

Both ecological and evolutionary processes shape biological communities along elevational gradients.The merging of phylogenetic information(evolutionary history)and functional traits provides a new perspective and idea for inferring community assembly processes.Soil animals as an essential part of the underground ecosystem,the studying its elevational patterns and community assembly is helpful to understanding the changing trend of soil ecological processes under the background of global change.The study was conducted in the Changbai Mountain,which with typical vertical natural vegetation zones,and focused on the ideal material for studying the geographical distribution of soil animals——Isotomidae.This study revealed the distribution pattern of Isotomidae along the elevational gradient,integrating ecological and evolutionary processes from three dimensions(taxonomic diversity,phylogenetic diversity and functional diversity)and two datasets(species abundance and species presence),withα,β of biodiversity research methods,combining environmental factors and spatial factors.The main results included:(1)Distribution pattern of species diversity along the elevational gradientA total of 29 Isotomidae species(three new species: Tetracanthella wui,Semicerura bryophila and S.draconis)of 13 genera were identified from a total of3,595 individuals,the number of genera accounts for one-half of the known genera in China(up to 2009,China has recorded 26 genera and nearly 70 species).Species richness,Shannon-Weiner index and Simpson index of Isotomidae community followed a hump-shaped pattern along the elevational gradient.Environmental(p H and soil temperature)and spatial variables significantly affected the species richness and composition of Isotomidae.For both abundance-weighted and unweighted measures,β-diversity increased significantly with elevational distance,and the richness differences(loss or gain of species)contributed more to the β-diversity.Spatial distance contributed more to richness differences than the environment,while environmental factors(such as soil temperature)contributed more to species replacement.(2)Distribution pattern of phylogenetic diversity along the elevation gradientThe phylogeny of Isotomidae was reconstructed based on mitochondrial genome sequencing,comparing the divergence time of the main clades and the uplift time of Changbai mountain,the results suggested that divergence events of most species occur before mountain uplift,except Isotoma pinnata and Desoria choi,whereas recent speciation is of little importance to community assembly of Isotomidae in Changbai Mountain.The phylogenetic diversity of the Isotomidae community showed a humpshaped pattern along the elevational gradient.Environmental(soil temperature)and spatial variables had significant effects on the variations of the community phylogenetic diversity along the elevational gradient,spatial variables contributed more than the environment to the changes.The phylogenetic structure(NRI and NTI)of the community showed a clustered distribution trend at most elevations.For both abundance-weighted and unweighted measures,the phylogenetic β-diversity increased significantly with elevational distance,and the information of phylogenetic differences(loss or gain of phylogeny)contributed more to the β-diversity.Environmental factors(soil temperature and carbon-nitrogen ratio)were the main drivers of phylogenetic beta diversity and species replacement,and spatial variables were the main drivers of phylogenetic richness differences.The above results showed that environmental filtering and dispersal limitation jointly regulate the distribution pattern of the phylogenetic diversity of the Isotomidae along the elevational gradient.Below-ground diversity in Changbai Mountain is mainly based on the persistence of old phylogenetic lineages,while recent speciation is of little importance.(3)Distribution pattern of functional diversity along the elevation gradientThe body length,developmental furca,number of ommatidia,and body pigmentation of Isotomidae showed strong phylogenetic signals.The functional diversity of the community was correlated positively with species richness,which showed a unimodal distribution pattern along the elevational gradient.The functionalβ diversity of Isotomidae and its partitioned components increased significantly with the increase of elevational distance,but the partitioned components did not change significantly after being weighted by the abundance.The variations of functional diversity,functional structure,and functional β-diversity of Isotomidae were mainly explained by the phylogenetic diversity.This indicated that the evolutionary history of the lineage significantly affected the functional diversity and their variation of the Isotomidae in Changbai Mountain,and the phylogeny diversity significantly correlated with environmental and spatial variables.The above results suggested that ecological processes and evolutionary processes jointly determine the pattern of functional diversity of the Isotomidae.In conclusion,ecological and evolutionary processes shape the community of Isotomidae along an elevational gradient in the Changbai Mountains.Environmental filtering and dispersal limitations were the main drivers,while recent speciation is of little importance.Integrating the phylogenetic and functional traits,considering abundance weighed or not and using α and β diversity methods help us to comprehensively understand the distribution pattern of biodiversity and its community assembly mechanism along the elevational gradient.The findings provide an essential scientific basis and dataset for the conservation of soil animal diversity resources in Changbai Mountain,and provide a new perspective for the study of below-ground biodiversity.