Plant Diversity And Ecosystem Functions In The Ebinur Lake Basin

Dryland ecosystem is one of the most fragile ecosystems on land.The response mechanism of ecosystem function to plant diversity and environment in drylands is an important issue in ecological research.Carrying out studies on the impact of biotic factors(taxonomic diversity,functional diversity and phylogenetic diversity)and abiotic factors(environmental factors)on ecosystem functions can reveal the mechanism of ecosystem functions more comprehensively and in-depth,especially has important theoretical value for the protection of plant diversity and the maintenance of ecosystem functions in dryland ecosystem.This study was conducted on desert ecosystem in the Ebinur Lake Basin by field community survey.We examined environmental factors and plant functional traits,calculated soil function indexes under the plant canopy,analyzed spatial distribution characteristics of the taxonomic diversity,functional diversity and phylogenetic diversity,and evaluated differences in community composition and their influencing factors.We,then,determined the effects of plant diversity on ecosystem multifunctionality at different levels.Finally,based on data of soil factors,taxonomic diversity,functional traits,and fertile island effect,we constructed the structural equation model of the community's fertile island effect,determined the driving factors of the fertile island effect,and revealed the plant diversity and its influence mechanism on ecosystem function.The main results are as follows:(1)The spatial distribution of soil organic carbon in the Ebinur Lake basin was strongly variable,with a total variation coefficient of 110.95%,and moderate intensity variations were tested in the soil moisture content,salt content,total nitrogen and total phosphorus.The variation coefficient of taxonomic diversity in herb plants was greater than in woody plants and community level.The variation of phylogenetic diversity indices at different level(community,woody and herb)were all small.The interpretation of soil physicochemical properties for species diversity,functional diversity and phylogenetic diversity of herbs was 31.42%,13.37%,20.01% and 20.56%,respectively,which were higher than those for community level and woody plants.PH significantly affects the taxonomic diversity,functional diversity and functional traits of community level and herb plants.Soil moisture had a significant effect on the functional traits of community level,woody plants and herb plants,whereas soil physical and chemical properties had no significant effect on phylogenetic diversity.We concluded that woody and herb plants had different responses to the environment,the maintenance of the community was affected by the niche process and the random process,herb plants were most sensitive to the soil physical and chemical properties,multiple aspects of plant diversity at different levels had different maintenance mechanisms.(2)The multifunctionality of community level and woody plant were mainly affected by the functional diversity and phylogenetic diversity,while herb ecosystem multifunctionality was mainly affected by taxonomic diversity.The effects of plant diversity on ecosystem multifunctionality and nutrient cycling were both selective and complementary.Soil moisture content was the main abiotic factor affecting the multifunctionality of the community ecosystem.In addition,the functional traits was the second factor which affect the ecosystem multifunctionality.The factors that affected the multifunctionality of woody plants were mainly the community weighted mean of functional traits and soil moisture content.While the main factors affecting multifunctionality of herbs were biotic factors,such as Shannon index,phylogenetic diversity and plant functional traits.The multifunctionality of woody plants and community level showed consistent pattern with the change of soil moisture,and it was demonstrated that the woody plant was the leader of the ecosystem multifunctionality.The strategy of ecological multifunctionality(and C,N,and P cycles)at different community levels were proposed as a "total is greater than a part" trade-off mechanism,that was,the community level was greater than the woody and herb layers.(3)The relative interaction indexes RII of nitrate nitrogen,?-glucosidase and alkaline phosphatase area were 0.54,0.28 and 0.23,respectively,showing a significant aggregation phenomenon.Different nitrogen-fixing plants had a significant difference in the fertile island effect between the threshold of 50%-90%,and different life form plants had a significant difference in the fertile island effect at the threshold of 90%,according to the classification of different functional groups of plants.However,the fertile island effect was not affected by the plant's photosynthesis type and canopy structure.The soil moisture content had significant correlation with the fertile island effect at community-level in range of 5%-71%,and the vegetation coverage between5%-99% was significantly positively correlated with the fertile island effect.These indicated the wetter the land and the higher the coverage,the greater the fertile island effect.The explanation of the effect of biotic and abiotic factors on the community's fertile island was 36.2% higher than that of the accumulation effect of C,N and P resources.The species richness,soil moisture and p H were the main driving factors of the fertile island effect,and soil salinity mainly affected the fertile island effect indirectly by affecting the species richness.We demonstrated that water was the key factor in the formation of the fertile island effect in our study area.Due to differences in mechanisms such as drought and salinization,there were differences in soil carbon,nitrogen,and phosphorus accumulation patterns.(4)Based on the community survey data from 2015 to 2017,the influencing factors of the species composition,indicator species differences,? diversity and species turnover,nestedness of the community were analyzed.The results showed that the annual herb richness and abundance were higher than in 2015 and 2017.Mulgedium tataricum and Halogeton glomeratus were unique indicator species in 2016.The Jaccard similarity index,Bray-Curtis similarity index and Chao similarity index of communities in 2016 and 2017 were significantly higher than the species composition difference index in 2015.The spatial distance explained the changes in community composition more than the soil factors and rainfall.The spatial distance,soil factors and rainfall together explained 42% of the changes in community composition.It revealed that the community composition was affected by the niche process and the random process.The observed values of ? diversity in different years showed that the high water gradient was greater than the low water gradient,and precipitation had the largest interpretation of ? diversity.The main explanation factor of the observed value of species turnover was also precipitation variation,and the biggest factor for species nestedness explanation was the interaction between year and water.Precipitation variation was the main factor explaining beta diversity,species turnover and species nestedness deviation.