Effects Of Water-souble Phenolic Compounds Of Eucalyptus Grandis On Soil Bacterial Community Structure

As the country with the largest area and the fastest growth rate of plantations in the world,the area of eucalyptus plantations is 4.5 million hm².Eucalyptus plantation exerts ecological and social benefits in providing forest products for humans and reducing atmospheric CO2 concentration.It also brings about ecological and environmental problems such as decreased biodiversity,decreased soil moisture and nutrient content,and the allelopathic effect is controversial.The research on the allelopathic mechanism of eucalyptus plantation is of great importance to the scientific management of eucalyptus plantation.Previously,the allelopathic effect of eucalyptus mainly focused on the physiological effects of plants,and lack of impact research on soil ecosystems.This is not systematic.Previous studies mostly concentrate on eucalyptus effects at a certain age,which is not conducive to comprehensively revealing the mechanism of eucalyptus allelopathy.This study used UPLC-MS to identify water-soluble phenolic compounds?phenolic acids and flavonoids?from Eucalyptus grandis plantation in the 2,4,6,8 and 10year-old eucalyptus plantations in Danling County,Sichuan Province.In order to provide a theories on scientific management of Sichuan Eucalyptus grandis plantations,analysing the correlations between these phenolic compounds and the characteristics of environmental factors in different age plantations,through the addition of phenolic compounds,finding out the impacts on soil bacterial community structure.The main results are as follows:?1?17 kinds of water-soluble phenolic compounds were identified by UPLC-MS in the litter,roots and rhizosphere soil of eucalyptus plantations.Among them,7 kinds of phenolic acids:2-O-Feruloyl hydroxycitric acid,6-Methylsalicylic acid,gallic acid,salicylic acid,ellagic acid,hydroxyphenyllactic acid,4-Hydroxybenzoic acid.10 kinds of flavonoids:chrysin,epicatechin,eriodictin,angoletin,epigallocatechin,sappanone A dimethyl ether,emodin,quercetin,tetrangulol,and biochanin A dimethyl ether.Most water-soluble phenolic compounds are higher in litters and roots than in rhizosphere soil.In addition,there was no significant difference in the content of most phenolic substances in the rhizosphere soil,but they were higher in the 6,8,and 10 year-old of eucalyptus litters,and higher in the 2 and 4 year-old eucalyptus roots.?2?Compared with abandoned farmland?AF?soil,the soil moisture content increased significantly in the 2-6 year-old eucalyptus,and the soil pH decreased significantly in the4-8 year-old Eucalyptus;soil nutrients?soil total nitrogen,soluble organic carbon,dissolved organic nitrogen,ammonium,nitrate and nitrite?were lower in the 2-4 year-old eucalyptus,and then increased significantly in the 6-10 year old eucalyptus.Compared with the AF,the soil nutrients content increased.In addition,the soil microbial biomass carbon content increased significantly after afforestation,and reached the maximum in the6 year-old eucalyptus.Soil microbial biomass nitrogen content increased significantly in the 2 year-old eucalyptus,and with the increased forest age,the soil microbial biomass nitrogen content decreased significantly.Compared with AF,the soil microbial respiration rate increased in different forest ages,and soil sucrase activity increased.The soil urease and nitrate reductase activity increased in the 2 year-old eucalyptus,and the soil nitrite reductase activity significantly reduced in the 8-10 year-old eucalyptus.?3?There is no significant difference in the total number of soil bacteria in different ages of eucalyptus and AF soil.The bacterial alpha diversity index of the 4 year-old eucalyptus increased significantly,while the bacterial alpha diversity index in 6-10 year-old significantly decreased.The bacterial community composition of the 2 and 6 year-old eucalyptus,4 year-old eucalyptus and AF,8 and 10 year-old eucalyptus were similar.The relative abundance of soil bacteria in each forest age was significantly different at the classification level of the phyla,class and genus.Among them,Gemm-1,Gemmatimonadetes,Betaproteobacteria and[Pedosphaerae]are the dominant class of 4year-old eucalyptus and AF.Gammaproteobacteria,DA052,Ktedonobacteria and ABS-6are the dominant class of 2 and 6 year-old eucalyptus.Alphaproteobacteria Clostridia and TM1 are the dominant class of the 8 and 10 year-old eucalyptus.The relative abundances of Betaproteobacteria,Gemmatimonadetes,[Pedosphaerae]and Gemm-1 were negatively related to most soil nutrients and biomasses?except nitrite reductase?.Ktedonobacteria,ABS-6,DA052,Gammaproteobacteria relative abundance were positively correlated with soil moisture content,nitrite reductase,and negatively correlated with soil inorganic nitrogen content.The relative abundance of Alphaproteobacteria,TM1 and Clostridia were positively correlated with soil inorganic nitrogen content,and negatively correlated with soil moisture content and nitrite reductase.the content of phenolic allelochemicals had significant correlations between and the dynamic changes of environmental factors?soil physical and chemical properties,biomass properties,bacterial community structure?with different eucalyptus ages.?4?Water-soluble phenolic compounds had inhibitory effects on soil organic carbon,total nitrogen,ammonium,nitrate,soil microbial respiration rate and nitrite reductase,while had stimulative effects on soil moisture content,pH,total phosphorus and dissolved organic carbon,nitrite,microbial biomass carbon,microbial biomass nitrogen,sucrase,nitrate reductase.Totally,the allelopathic effects of phenolic acids are generally stronger than flavonoids.6-methylsalicylic acid,gallic acid and epicatechin had stronger effects on soil physical and chemical properties and biomass properties,while hydroxyphenyllactic acid had a weak allelopathic effect on soil physical and chemical properties and biomass characteristics.The remaining phenolic allelochemicals had middle level allelopathic effects on soil physical and chemical properties and biomass properties,and not strong.?5?The allelopathic effects of phenolic acids on soil bacterial community structure was stronger than that of flavonoids.Among them,6-methylsalicylic acid and gallic acid promoted the total number of soil bacteria;6-methylsalicylic acid in C1 concentration,gallic acid in C4 concentration,epicatechin and epigallocatechin had stimulative effects on soil bacteria Alpha diversity index,while salicylic acid,ellagic acid and emodin in C1concentration had inhibitory effects on soil bacterial Alpha diversity index.Except for4-hydroxybenzoic acid,phenolic acids can distinguish the soil bacterial community composition with high concentration,low concentration treatment and AF,while most flavonoids?except emodin?cannot separate the soil bacterial community.Gallic acid,salicylic acid and ellagic acid had great effects on the relative abundance of different soil bacteria.Gallic acid had positive effects on the relative abundance of unidentified_Actinobacteria and Ktedonobacteria,and had negative effects on relative abundance of Subgroup₂,unidentified_Acidobacteria?C1 concentration?and Alphaproteobacteria.Salicylic acid promoted the relative abundance of Betaproteobacteria?C1 concentration?and inhibited the relative abundance of Subgroup₂.Ellagic acid promoted the relative abundance of unidentified_Actinobacteria,while inhibited the relative abundance of Subgroup₂,unidentified_Acidobacteria and Alphaproteobacteria in C1 concentration treatment.In addition,most phenolic compounds had promoting effects on the relative abundance of Betaproteobacteria.The promotion of phenolic acid was stronger than that of flavonoids.Most phenolic compounds had inhibitory effects on the relative abundance of Clostridia.The relative abundance of Alphaproteobacteria is positively correlated with soil pH?gallic acid,ellagic acid,chrysin?,nitrate nitrogen content?except for hematoxylin dimethyl ether?.In the treatment of chrysin and sappanone A dimethyl ether,Alphaproteobacteria was positively correlated with sucrase activity,but negatively correlated with sucrase activity in gallic acid,salicylic acid,and ellagic acid treatment.Alphaproteobacteria was inversely related to the relative abundance of Betaproteobacteria?except emodin?.The relative abundance of Betaproteobacteria was positively correlated with soil pH in the treatment of hydroxyphenyllactic acid,gallic acid,chrysin and epigallocatechin,while in the treatment of epicatechin and epigallocatechin Betaproteobacteria was negatively correlated with nitrate and ammonium.The relative abundance of Betaproteobacteria increased in most phenolic acids?except gallic acid,ellagic acid?,chrysin,sappanone A dimethyl ether and epicatechin.The relative abundance of Clostridia was positively correlated with the content of nitrate?except salicylic acid and chrysin?,ammonium?except hydroxyphenyllactic acid,gallic acid,salicylic acid and chrysin?and soil microbial respiration rate?4-hydroxybenzoic acid,6-methylsalicylic acid,gallic acid,epicatechin,epigallocatechin?,while was negatively correlated with microbial biomass carbon content?6-methylsalicylic acid,Ellagic acid,chrysin,emodin,sappanone A dimethyl ether and epicatechin?,soil moisture content(6-methylsalicylic acid,gallic acid,ellagic acid,quercetin,epicatechin and epigallocatechin.In summary,the content of water-soluble phenolic compounds in eucalyptus varied significantly by the affects of forest and soil environmental factors.Phenolic compounds significantly affected soil bacterial community structure,soil physical and chemical properties and biomass characteristics.6-Methylsalicylic acid,gallic acid,salicylic acid,ellagic acid and epicatechin are the main water-soluble phenolic allelopathic compounds of Eucalyptus grandis plantations.These results revealed allelopathy of Eucalyptus grandis plantations and provided methods of management theoretical basis.