Ecological Effects Of The Utilization Of Sewage And Sewage Sludge On Microbes In Soil

Microorganisms are receiving increasing recognition for their essential ecosystem functions,such as biogeochemical cycling,sustaining soil nutrient status,as well as monitoring environmental quality.Effects of heavy metals(HM)pollution of soil on soil microorganisms were paid attentions to by many researchers in recent years. Changes in microbial diversity may have an important influence on soil ecosystems, and some microbial parameters can monitor HM pollution in soil.For agricultural soil, sewage irrigation and sewage sludge(SS)application was an important source of HM. Because some kinds of sewage and SS are valuable sources of plant nutrients and organic matter,and can enhance soil fertility and save water resource.However,heavy metals become concentrated even polluted through long-term use of sewage or SS.The systemic studies of microbial ecology are useful to the reasonable use of sewage and SS.Experiments were designed based on the practice conditions of sewage irrigation and SS application in Shandong Province.Firstly,the field research selected Boxing County which lies at the middle of the Valley of Xiaoqing River.The effects of long-term sewage irrigation on soil and soil microorganisms were studied.Secondly, based on the investigations of field experiment,a series of greenhouse pot experiments were conducted to simulate the accumulation of HM(the concentration of HM was based on the SS enriched with Cd,Cu,Zn and Hg)with long-term use of sewage and SS by adding HM salts,and the influences of HM on soil microorganisms were studied. Meanwhile,considering the effects of the crops,the effects of HM on microorganisms in rhizosphere were studied by rhizobox method.The methods of basal respiration, microbial biomass,community level physiological profiles(CLPP)and fatty acid methyl esters(FAME)were selected to assess the soil microorganisms.The results were shown as follows:1.Effects of long-term sewage irrigation on on soil microbial community Soil samples taken from a sewage irrigation area,a partial sewage irrigation area and a ground water irrigation area(control area)were studied with the methods of Biolog and FAME.It was found that the microbial utilization of carbon sources in sewage irrigation areas was much higher than that of control area(P＜0.05).With the increasing of the amount of sewage irrigation,microbial functional diversity slightly increased by the Biolog analysis,however,the amount of epiphyte decreased by the FAME analysis.The results also showed that the Cr,Zn contents were positively correlated with the values of AWCD and the microbial diversity.While Hg content showed negative correlation with the microbial parameters(AWCD of 72 h and shannon index).Our studies suggested that sewage irrigation resulted in obviously increase of heavy metals contents in soil(P＜0.05),although the maximum heavy metals concentrations were much lower than the current standard of China.Other soil basic characteristics such as cation exchange capacity(CEC),total nitrogen(N_t)and organic matter in sewage irrigation areas obviously increased(P＜0.05).Therefore,it is demonstrated that the long-term sewage irrigation had influenced soil microorganisms and soil quality in the studied soils.As a result,it is important to monitor the environmental changes in agricultural soils.2.Influences of sewage sludge enriched with heavy metals on soil microbial community.Five treatments(control,soil + 20%SS,soil + 40%SS,soil + 20%SS + 5×HM, soil + 20%SS + 10×HM)were used to simulate the accumulation of HM with long-term use of SS by greenhouse pot experiments.The results showed that the biomass of wheat and corn in control was much higher than that of the treatments with SS(P＜0.05).The uptake of Cd,Cu,Zn and Hg with tissues of wheat and corn increased with increasing amounts of HM.The concentrations of the HM in roots were higher than those of stems and leaves.The results also showed that organic C(C_org) and total nitrogen(N_t)of the soil significantly increased with SS application,while pH significantly decreased(P＜0.05).After treated by SS,the values of BAS,C_micand C_mic/ C_orgdecreased with increasing amounts of HM in wheat soil,and the value of BAS,C_micand C_mic/ C_orgincreased in corn soil.However,there was no significant difference in all results.The PCA analysis of the soil quality in treatments with planting wheat showed that the difference of the fives treatments came from Cd,Cu, Zn,Hg and pH,while in treatments with planting corn the difference came from Cu, Zn,pH,C_organd N_t.The results also indicated that the corn was better influenced by the C and N in SS than that of the wheat.The results from CLPP showed that AWCD obviously decreased(P＜0.05)with increasing amounts of SS in wheat.However, AWCD did not have regular changes in corn treatments.The PCA analysis of CLPP showed that the control had greater utilization of the carbon sources than the treatments with SS and HM,and high SS treatment(soil + 40%SS)had little utilization of the carbon sources.The result also showed that high application rate of SS and HM in this study weakened the difference between the rhizosphere and non-rhizosphere.In rhizosphere,functional diversity(H′and E)did not have obvious changes.The result showed that SS application had a beneficial effect on the soil fertility,even benefit for BAS and C_micin some treatments.But the negative effect of HM accumulation is not ignored.Therefore,it is necessary to have a small quantity application rate and remove the HM from SS for long-term use in cropland.3.Influences of simulation sewage enriched with heavy metals on soil microbial community.Three treatments(control,soil + 6×HM,soil + 11×HM)were used to simulate the accumulation of HM with long-term sewage irrigation by greenhouse pot experiments.Wheat and corn as two normal crops were planted,and effects of simulative sewage on microorganisms in rhizosphere were studied.The results showed that the biomass of wheat and corn significantly decreased with increasing amounts of HM(P＜0.05).The uptake of Cd,Cu,Zn and Hg by wheat and corn increased with increasing amounts of HM.The concentrations of the HM in the roots were higher than those of stems and leaves.Treatments with HM had a high TF_rootof Hg.The results also showed that pH significantly decreased with increasing amounts of HM(P＜0.05). In the treatments with planting wheat,high concentration of HM significantly decreased C_org,but C_micand C_mic/ C_orgsignificantly increased(P＜0.05).In the rhizosphere of the corn,C_org/ N_t increased firstly and obviously latterly decreased with increasing amounts of HM(P＜0.05),however,BAS obviously decreased in non-rhizosphere(P＜0.05).The results from CLPP showed that AWCD slightly decreased with increasing amounts of HM.The PCA analysis of CLPP showed that the control and the treatments with low concentration of HM tended to have better utilization of majority carbon sources than that of the treatments with high concentration of HM.Microorganisms in rhizosphere had better utilization of carbon sources than that of non-rhizosphere.Functional diversity(H'and E)did not have obvious changes.The correlation analysis of wheat showed that pH was negatively correlated with C_mic.C_orgwas negatively correlated with BAS,but it was positively correlated with the values of AWCD in 72 h and 120 h.Available Cu and Zn contents were positively correlated with C_mic,and available Cd content showed positive correlation with PC1,while available Hg content showed negative correlation with H′. The correlation analysis of corn showed that available Cu and Zn contents were negatively correlated with C_mic,while available Hg content showed positive correlation with PC2.The root biomass of corn was positively correlated with pH,but it was negatively correlated with available Cu and Zn contents.The result showed that simulative sewage did not have a serious effect on the soil microorganisms,even benefit for some microbial parameters in treatments with planting wheat.However,the negative influence on corn was obvious.But the negative effect of HM accumulation is not ignored.Moreover,high concentration of HM in this study lowered the difference between the rhizosphere and non-rhizosphere.All results indicated that accumulation of HM with long-term sewage irrigation had changed ecology balance of soil microorganisms.Therefore,it is necessary to remove the HM from sewage for long-term using in cropland.4.Influences of non-heavy metals factors in sewage sludge on soil microbial community.The four treatments(soil + 20%SS + 5×HM,soil + 20%SS + 10×HM,soil + 6×HM,soil + 11×HM)had the same concentration of HM,so the effects of factors in SS except HM to soil microorganisms could be found from these treatments.The results also showed that C_organd Nt of the soil significantly increased with SS application,but pH significantly decreased(P＜0.05).In the rhizosphere of the wheat, Craig,BAS and C_mic/ C_orgincreased with increasing amounts of HM.C_micwith SS decreased,BAS increased,while C_mic/ C_orgsignificantly decreased(P＜0.05).In the rhizosphere of corn,C_micand BAS decreased with increasing amounts of HM in the treatments with HM only,but increased in the treatments with SS.In rhizosphere of wheat,available Cd content had positive correlation with BAS,and available Hg content had positive correlation with C_mic.In the rhizosphere of corn,N_t and C_orgwere positively correlated with C_micand BAS.pH had negative correlation with shannon index E,while N_t and C_orghad positive correlation with E.The results indicated that the effects of factors in SS except HM to soil microorganisms in the rhizosphere of corn was more great than that of wheat,while the effects of HM to soil microorganisms in the rhizosphere of wheat was more great than that of com.5.Comparison of different methodsIn the field experiment,CLPP and FAME methods could differentiate microbial structure in soil,and the contents of Cr,Zn and Hg had correlation with AWCD and microbial function diversity index.It is confirmed that the methods of CLPP and FAME are effective tools for the assessment of soil microbial structure/function and soil health.In greenhouse experiments,CLPP method could differentiate microbial structure in soil.However,microbial function diversity index did not change obviously. The other methods such as C_mic,BAS and C_mic/ C_orgshowed the influences of SS and HM on soil microorganisms in different aspects.In summary,crops,soil quality and HM affected the microbial community by influencing survival environment of soil microorganisms.It is unilateral to determine single microbial parameter as whole reflection of soil microorganisms.Therefore,the combination of several methods is recommended for describing the general characteristics of microbial communities.