| The relationship between biodiversity and ecosystem function has always been the core issue of ecological research.At present,researches on the relationship between plant diversity and single ecosystem function are mostly focused on exploring the relationship between plant diversity and single ecosystem function,while ignoring that ecosystem can provide multiple functions and services at the same time,that is,it has ecosystem multifunctionality,and is affected and regulated by aboveground and underground biodiversity at the same time.The Loess Plateau is the most vulnerable area of ecological environment in China.Caragana korshinskii plantation is an important measure of ecological restoration in the Loess Plateau.Its planting and growth have been proved to play a significant role in improving the biodiversity and ecosystem function of vulnerable habitats.However,there is still a lack of research on the relationship between ecosystem multifunctionality and biodiversity of Caragana korshinskii plantation ecosystem.In this study,Caragana korshinskii plantation with different planting density was selected as the research object in the southern mountain area of Ningxia,which is the key planting area of Caragana korshinskii on the Loess Plateau.We systematically investigated the biodiversity(plant,soil microorganism and nematode community)and ecosystem functions(including plant biomass,organic carbon storage,nutrient cycling and water holding function)in different Caragana korshinskii forests,and further analyzed the relationship between them.The results show that:(1)In different planting density,the aboveground and underground biodiversity of Caragana korshina plantation were significantly different,but there was a close relationship between them.With the decrease of planting density of Caragana,the coverage and root biomass of herbaceous plants decreased gradually.But Margalef richness index and Shannon diversity index were lower than other plots in high density forest MD1 and low density forest MD4,and it was related to the higher important value(>50%)of the grass plants(Stipa bungeana)between the two plots.Caragana korshinskii planting density had little effect on soil bacterial community composition and diversity,while fungal community richness(OTU number and Chao1 index)was significantly higher in high-density forest MD1 and low-density forest MD4 than in other plots.Correspondingly,the relative abundance and diversity of bacteriophagous nematodes were not significantly different in different areas,while the relative abundance and Margalef richness index of fungal nematodes showed similar trends with that of fungal communities.Phytophagous nematodes were the dominant trophic group,the relative abundance and Margalef richness index of phytophagous nematodes in MD1 and MD4 plots were lower than those in other plots,showing a consistent trend with the richness and diversity of plant species.The abundance of omnivorous predatory nematodes reached the highest value in the MD1 plot and decreased to the lowest value in the MD4 plot.The highest comprehensive index of soil biodiversity(based on OTU number of soil bacteria and fungi,and Margalef richness index of nematodes)appeared in MD1 sample plot of high-density forest(0.885),followed by MD4 sample plot of low-density forest(0.119),showing a significant negative correlation with species richness index of herbs under Caragana korshinskii forest.(2)The ecosystem function and ecosystem multifunctionality of Caragana korshinskii plantation in plant growth(biomass),nutrient cycling,organic carbon storage and water conservation were significantly affected by its planting density,which was related to the number of Caragana korshinskii plants per unit area of Caragana korshinskii plantation with different planting density.In MD1 plot of high-density forest(20000 clusters/hm~2),the number of Caragana korshinskii plants per unit area was the highest,resulting in the highest biomass of Caragana korshinskii(35.03t/hm~2)and litter(4.34t/hm~2),which directly promoted the increase of organic carbon,total nitrogen and total phosphorus storage of Caragana korshinskii plants and litter,and by improving the input of soil resources,the contents of soil organic carbon,nitrogen and phosphorus and soil water content were increased.Therefore,the ecosystem function index of Caragana korshinskii plantation in plant growth,nutrient accumulation,organic carbon storage and water conservation reached the highest in high-density Caragana korshinskii forest MD1,and showed a significant downward trend with the decrease of Caragana korshinskii planting density,indicating that there was a synergistic effect between different ecosystem functions of Caragana korshinskii plantation.Accordingly,the change trend of ecosystem multifunctionality index was MD1>MD2>MD3>MD4,and the comprehensive index of MD1 sample plot(0.842)was significantly higher than that of other sample plots,which indicated that the higher density of Caragana korshinskii plantation had better ability to provide and maintain multiple ecosystem functions and services at the same time.(3)Compared with aboveground plant diversity,underground biodiversity has a more significant impact on ecosystem function.The evenness index of plant community,the richness and diversity index of bacterial community,the comprehensive index of soil biodiversity were significantly positively correlated with plant biomass,organic carbon storage,nutrient cycling and water holding function index,while only out quantity in fungal community was significantly correlated with nutrient cycling function index;Margalef richness index of nematode community was positively correlated with water holding function,while Shannon diversity index was negatively correlated with plant growth function index,and positively correlated with nutrient cycling and water holding function index;For different trophic groups of nematodes,the diversity indices of phytophagous nematodes and omnivorous predatory nematodes were more closely related to ecosystem functions,This may be related to the root feeding function of phytophagous nematodes and the control function of omnivorous predatory nematodes.The diversity index of bacterial community was significantly positively correlated with ecosystem multifunctionality,and the Pielou evenness index of plant,Margalef richness index of omnivorous predatory nematode and the comprehensive index of soil biodiversity were also significantly positively correlated with ecosystem multifunctionality.Caragana korshinskii planting density directly or indirectly affects the ecosystem multi-function by regulating the diversity of aboveground plants,soil bacteria and nematodes. |
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