The Effects Of Elevated CO₂ Concentration On C And N Transformation In The Soil Of Tea Plantation And Eutrophic Water

Elevated atmospheric CO₂ concentration?eCO₂?is the main cause of greenhouse effect,which will result in deterioration of the global climate and environment,and have an important impact on C and N biogeochemical cycles.The extensive application of N fertilizer in tea plantation would lead to N element accumulation in the soil and eutrophication in the nearby water bodies.The eCO₂ could affect C and N transformation by promoting the photosynthesis of tea plants,and inputting more plant-derived C to the soil,thereby affecting the activity,composition and function of microbial community,it also had direct or indirect impact on C and N cycle in bare soil and nearby eutrophic water.In economic forest ecosystem,the effects of eCO₂ on C and N transformation would directly affect the efficiency of nitrogen utilization of tea plants and the ecological benefits of tea plantation and eutrophic water bodies.Microcosm experiments,high-throughput sequencing and stable isotope tracer technique were used to study the effects of eCO₂ on nitrification,denitrification,and carbon conversion processes in the soil of tea plantation and eutrophic water.The changes of microbial community involved in nitrification,denitrification,CO₂ assimilation and C degradation process were also investigated to explore how the process of C and N transformation coupled with microbial community in the soil of tea plantation and eutrophic water under eCO₂ condition.The research would provide valuable information for theoretical guidance on how to maximize the ecological benefits for tea plantation and economic forest under the context of global greenhouse effect.The results were as follows:1.The eCO₂ significantly increased the aboveground and underground biomass of tea and promoted the germination and growth of tea leaves,but had no significant effect on the height of seedling.The eCO₂ promoted the absorption of tea roots on N element from soil,but had no significant effect on C content of the tree and on N content of aerial part.2.With or without the growth of tea,the eCO₂ significantly contributed to the increase of CO₂ fixation gene?cbbL?associated to the Calvin cycle.No matter whether elevation of CO₂concentration,the growth of tea increased the abundance of functional gene related to C decomposition?ChiA,GH48 and cbh??.With the growth of tea,eCO₂ promoted the increase of LOC,MBC content and the abundance of GH48 gene in the soil,and promoted C degradation.3.With or without the growth of tea,eCO₂ decreased the content of TDN and NO₃^-,and increased the abundance of functional gene related to denitrification?nirS,nirK and nosZ?,promoting denitrification in the soil.Without the growth of tea,eCO₂ promoted N₂O emissions.With the growth of tea,the N₂O emissions was much higher under eCO₂ condition than that in the treatments without plants,but lower than that in the treatment of with the growth of tea under aCO₂condition.4.With or without the growth of tea,eCO₂ increased the relative abundance of photosynthetic bacteria in soil,e.g.cyanobacteria and chloroflexi,promoted CO₂ assimilation by photoautotrophy.Nitrifying bacteria and ammonia-oxidizing bacteria had similar trend responding to eCO₂ and the growth of tea.However,the relative abundance of Thaumarchaeota,Nitrospinae,Nitrospirae and Nitrososphaeraceae were lower under the synergy of eCO₂ and the growth of tea than that in the aCO₂P and eCO₂ treatment.Under aCO₂ condition,the growth of tea significantly increased the abundance of Bacteroidetes?Bacteroidia?,Chitinophagales,Cytophagales which were bacteria typically involved in C decomposition,and promoted C decomposition in soil.The synergy of eCO₂ and the growth of tea increased the abundance of C-degrading bacteria?Fibrobacteres,Bacteroidetes,Chitinophagaceae,Sphingobacteriaceae,Sphingomonadaceae?and C-degrading bacteria with denitrifying properties?Vibrionales,Vibrionaceae,Vibrio,Xanthomoandaceae,Sphingomonadaceae?,led to the increase of C degradation and denitrification in soil and accelerated the flux of C and the rate of C transformation in soil.5.With or without the growth of tea,eCO₂ decreased the relative abundance of Ascomycota fungi and increased the relative abundance of Basidiomycota fungi.With the growth of tea,the relative abundance of soil saprophytic and wood saprophytic fungi was higher under eCO₂condition,and lignin degradation by fungi was promoted.6.Nitrification may be slightly inhibited by eCO₂ in the eutrophic water and this was mainly due to the competition for dissolved inorganic carbon between algae and nitrifiers.On the other hand,eCO₂ promotes denitrification and N₂O emissions from eutrophic water without growth of plants,leading to aggravation of greenhouse effect and forming a vicious cycle.The pH was regulated through diurnal photosynthesis and respiration of algae and mitigated the acidification of water caused by eCO₂,leading to an appropriate pH range for both nitrifying and denitrifying microbes.Algal respiration at night consumed DO and enhanced abundance of denitrifying functional genes?nirK,nosZ?in water,which was also supposed to be a critical factor affecting denitrification and N₂O emissions.7.eCO₂ significantly increased the abundance of bacteria and functional gene involved in CO₂ assimilation?photosynthetic bacteria;cbbL?and C decomposition?Acidimicrobiia,Thermoleophilia,Gaiellales;ChiA?in the eutrophic water,showing functional enrichment in photoautotrophy,hydrocarbon degradation,cellulolysis,and aromatic hydrocarbon degradation.However,eCO₂ decreased the abundance of chemoautotrophic bacteria including nitrifying bacteria?Nitrosomonadaceae,Nitrospirae?in the eutrophic water.There were similar or different effects of eCO₂ on C and N transformation in the soil and water of tea plantation.Without plants,eCO₂ promoted denitrification and N₂O emissions in the soil and water of tea plantation,which may lead to the aggravation of greenhouse effect.In addition,CO₂ assimilation and C decomposition had positive response to eCO₂,which would accelerate the flux of C and the rate of C transformation.In addition,there were stronger response of C and N transformation in the soil to eCO₂ with the growth of tea plants.The abundance of functional gene and related bacteria involved in denitrification,CO₂ assimilation and C decomposition was higher.These results supported the further understanding on the difference of C and N transformation in the varied media within the same system and the role of plants in the process of C and N transformation under the context of global greenhouse effect.