Effects Of Reclamation On Functional Structure Of Soil Fauna Community In Hengsha Island,shanghai

Mudflat reclamation is the main land uses in coastal areas.As the parent materials come from the ocean,the newly reclaimed land is often high in salinity and low in nutrient content.With the improvement of soil physicochemical properties with increasing reclamation time,the composition of plant and animal communities will change regularly.Therefore,the soil chronosequence formed by different reclamation times is ideal for studying how human land use and natural processes affect the dynamics of plant and animal communities.Soil fauna are the key participants of soil ecological function during tidal flat reclamation.Due to the change of soil properties and vegetation composition in different reclamation stages,the community structure and functional strategy of soil fauna also change significantly.Although several studies have investigated the variations of vegetation and soil fauna community structure during reclamation,limited by the complexity and availability of functional traits of soil fauna,the studies on the effects of reclamation on functional structure and community assembly of soil fauna are still lacking.In this study,the following reclamation land reclaimed at five different times were selected in Hengsha Island of Shanghai,including the bare fields in 1-yr reclaimed land,the halotolerant plant community of Tamarix chinensis in 3-yr reclaimed land,the grassland in 5-yr reclaimed land,the secondary forests in 10-yr reclaimed land and the secondary forests in 50-yr reclaimed land,to study the variations of soil fauna community and functional structure during reclamation and the driving factors.From2019 to 2020,the community composition of soil nematodes,mites and collembolans were investigated at different reclamation stages in four seasons together with the investigation of plant community composition and soil physicochemical properties.The morphological and life history functional traits related to locomotion,dispersal,environmental tolerance and resource requirement were measured and compiled,including body size,cuticle feature,locomotion organ,life history strategy,sensory organ,feeding guild and others.The main results are as follows:1.In this study,50 genera of soil nematodes,58 genera(or families)of mites and21 genera of collembolans were collected.With the increase of reclamation age,soil organic matter,total nitrogen,plant coverage,plant species richness and underground root biomass increased,while soil p H,electrical conductivity and bulk density decreased.The changes in vegetation structure and soil fertility significantly affected the community structure of soil fauna during reclamation.The diversity of three groups of soil fauna increased with reclamation age,but the change patterns of taxonomic composition were significantly different.Soil nematodes could rapidly colonize the initial reclamation stage and adapt to several habitats in different stages.Mesodorylaimus and Acrobeloides were dominant at the 1-yr to 10-yr stages,while Helicotylenchus was dominant at the 50-yr stage.The community composition of mite changed significantly at different stages,with the shift of dominant taxa from Prostigmata,Endeostigamta or Astigmata at the early stages to Mesostigmata at the middle stage,and then to Oribatida at the late stages.Soil collembolans could hardly colonize bare field at the 1-yr reclamation land.Isotomurus,Proisotoma and Folsomides were the dominant taxa at the early stages,but the dominant taxa shifted to Folsomina,Folsomia and Thalassaphorura at the late stages.2.The functional composition of three groups of soil fauna significantly changed during reclamation.With the increase of reclamation age,the proportion of r-strategists and bacterivores decreased while the proportion of K-strategists,fungivores and herbivores increased.However,there was no significant change in body size,tail length,amphid and cuticle annulation.For the mite community,the body size,cuticle sclerotization level and the proportion of K-strategists and primary decomposers increased while the proportion of phoretic mites decreased.The early colonizers of soil collembolans were predominantly edaphic collembolans with large body size and developed furca,pigmentation and ocelli,while the collembolans at the late stages were mainly fungivous euedaphic collembolans with reduced furca,pigmentation and ocelli,and developed post-antennal organ and pseudocelli.Multiple linear regressions indicated that plant species richness,plant coverage,root biomass and soil organic matter were the main factors driving the change of soil fauna traits during reclamation.3.The analysis of the community assembly mechanism based on functional traits showed that the multi-trait functional diversity of nematodes did not change with the reclamation stage,suggesting the influence of neutral random processes.In contrast,the multi-trait functional diversity of mites and collembolans changed from convergence at the early stages to divergence at the late stages,indicating that the dominant community assembly processes shifted from environmental filtering to interspecific competition.The analyses on single trait diveristy demonstrated that the feeding guild of nematodes,most traits of mites and the furca,post-antennal organ and pseudocelli of collembolans all followed the pattern of the shift from convergence at the early stages to divergence at the late stages.However,the traits of mites tended to converge at the 50-yr stage,which might be resulted from asymmetric competition.Multiple linear regression showed that the increase of stressors such as soil p H and bulk density generally led to trait convergence,while the increase of plant species richness,plant coverage and soil organic matter generally led to trait divergence.However,the increase of soil organic matter led to trait convergence of mites,which might be caused by the asymmetric competition of dominant groups for organic matter resources.In conclusion,this study systematically revealed the effects and mechanisms of coastal mudflat reclamation on the dynamics of community structure,functional composition and functional diversity of soil micro and mesofauna.The results showed that with the change of vegetation composition and the improvement of soil quality,the community strucutre,functional composition and functional diversity of soil micro and mesofauna changed significantly.The resource limitation and environmental stress at early stages constrained soil fauna diversity,and environmental filtering selected for functional traits of higher dispersal ability,tolerance and faster growth rate.At the late reclamation stages,the increase in resource availability and interspecific competition promoted higher soil fauna diversity.The results of this study deepen our understanding of the temporal and spatial dynamics of the functional structure and the community assembly mechnisms of soil fauna community,and provide research support for ecological restoration and biodiversity conservation in coastal reclamation areas.