Study On The Maintenance Mechanism Of The Ecosystem Multifunctionality In Littoral Zone Wetlands Of The Daihai Lake

The study of the relationship between Biodiversity and Ecosystem Multifunctionality（BEMF）has been a hot area of interest for ecological research in recent years.Changes in biodiversity are non-randomly distributed in space and time of natural ecosystems,and the relationship between biodiversity and ecosystem multifunctionality is affected by a combination of biotic and abiotic factors.And it shows complex and uncertain relationships affected by research scale,quantification and measurement indicators.This paper took the typical lake Daihai littoral zone wetlands in Inner Mongolia as the research object,and revealed the characteristics and processes of dynamic succession of wetland vegetation and ecosystem function changes during the lake shrinking process.Based on the distribution characteristics of soil environment factors（water and salt）,the study area was divided into four water and salt gradients:extremely high water and salt（EHWS）,high water and salt（HWS）,medium water and salt（MWS）and low water and salt（LWS）.The climate,plant community composition,plant functional traits,soil environmental factors,and microbial diversity data obtained from field experiments,laboratory experiments and amplicon sequencing would elucidated the maintenance mechanism of the multifunctionality in Daihai littoral zone wetland ecosystems.The main research results and conclusions were as follows:1.The aboveground species and functional diversity were shown as medium water and salt（MWS）>low water and salt（LWS）>high water and salt（HWS）>extremely high water and salt（EHWS）;The aboveground（species,functions）and belowground（bacteria,fungi）biodiversity showed significant differences in different water and salt gradients.The significant positive correlations were presented between aboveground species and functional diversity,aboveground and belowground biodiversity;The results of the variance partitioning analysis showed that the aboveground species and functional diversity,and belowground soil bacterial diversity were jointly driven by both（physical and biochemical indicators）,and the shared explanation rates accounted for 66%,56%,and 68%,respectively.Soil physical indicators affected aboveground species and functional diversity more than the biochemical indicators,respectively 16%>7%,17%>9%,and soil biochemical indicators affected bacterial and fungal diversity more than the physical indicators,respectively 6%>2%,19%>12%.Soil salinity（EC）,soil moisture（SM）,soil enzyme activity（S-β-GC,S-UE,S-AKP）were important soil environmental factors that affected aboveground and belowground biodiversity in littoral zone wetlands.2.The medium and low water salt plots had higher microbial richness and diversity.The microbial community composition in medium water salt（MWS）and low water salt（LWS）plots were similar,the extremely high water salt（EHWS）and high water salt（HWS）plots were similar,and had greatly different from each other.Soil salinity（EC）,soil moisture content（SM）,aboveground biomass（AGB）,belowground biomass（UGB）,soil clay（Clay）,soil available potassium（AK）,soil urease（S-UE）were the main soil environmental factors affected the bacterial and fungal communities at the level of phylum.The bacterial community Acidobacteriota and the fungal community Ascomycota were significantly and positively correlated with EMF,and the unclassified fungal phylum was significantly and negatively correlated with EMF.The three could be well explained EMF changes in littoral zone wetlands.The dominant microbial community composition regulated EMF and C,N,P cycling changes,and the bacterial community was more sensitive than the fungal community.3.Based on two years of field sampling experiments,the productivity and aboveground biodiversity（Margalef,Shannon,Rao,FDis indices）showed medium water and salt（MWS）>low water and salt（LWS）>high water and salt（HWS）in littoral zone wetlands.Growing season precipitation had a direct negative effect on plant productivity（λ=-0.13）,water and salt gradients had a direct positive effect on plant productivity（λ=0.22）;Growing season precipitation and water-salt gradients could also indirectly affect plant productivity by plant functional traits community-weighted mean(CWM_PH,CWM_RCC/RNC),species richness（Margalef）,functional diversity（FDis）,and soil environmental factors（S-AKP,EC）.The species richness played an important role in maintaining the productivity.The productivity of littoral zone wetlands was affected by both selection effect and ecological niche complementarity effect,and they had opposite relationships.Selection effect(CWM_PH,CWM_RCC/RNC)could better interpret and predict the changes of productivity in littoral zone wetlands.4.Ecosystem multifunctionality index was showed low water and salt（LWS）>medium water and salt（MWS）>extremely high water and salt（EHWS）>high water and salt（HWS）in littoral zone wetlands.There were no significant difference between the low water salt（LWS）and medium water salt（MWS）plots,and were significant differences among the other plots.The combined effects of aboveground（species,functional）and belowground（bacterial,fungal）biodiversity were greater than the effect of their single component on EMF（R²=80.00%）.Soil salinity（EC）had a direct negative effect with EMF（λ=-0.22）,soil moisture（SM）had a direct positive effect with EMF（λ=0.19）,EC and SM could indirectly impact EMF through aboveground and belowground biodiversity.5.Plant species Margalef index was an ideal indicator to characterize the EMF and C,N,P cycling functions in littoral zone wetlands.The quality ratio hypothesis selection effect(CWM_LCC,CWM_RV,CWM_RNC)could better explain the changes of EMF and C,N,P cycling than the ecological niche complementation effect（FDis）in the functional diversity.EMF,C and P cycles were mainly influenced by bacterial diversity,and N cycle was mainly influenced by fungal richness in belowground biodiversity.Plant species richness and sand content affected EMF through multiple nutrients（functional diversity,plant functional traits community-weighted mean,bacterial and fungal richness and diversity）cascading effects in littoral zone wetlands.In conclusion,there were significant differences in aboveground and belowground biodiversity,microbial community composition,and ecosystem multifunctionality among the different water and salt gradients in littoral zone wetlands.External environmental changes drived plant and microbial diversity to regulate productivity and ecosystem multifunctionality.This paper provided a reference for theoretical research on the maintenance mechanism of ecosystem multifunctionality in natural littoral zone wetlands under the background of global change,and also provided important theoretical support and basic data for the implementation of the national strategy for ecological restoration in Daihai littoral zone wetlands.