Effects Of Exogenous Additives On Hormesis Effect Of Cd Induced Soil Respiration

Hormesis refers to the phenomenon that organisms will respond to stimulation when exposed to low concentrations of stress,and are inhibited at high concentrations.In recent years,in order to further explore the expression of hormesis at the ecosystem scale and its potential pollution remediation value,hormetic research is shifting from traditional biological objects to more complex biotic-abiotic complexes.Soil is the most complex biotic-abiotic complex known to date.The study shows that using soil itself as an experimental model,soil enzymes and soil microbial communities as test endpoints,can well explore the hormetic effects at the soil ecosystem scale.Soil respiration is a process in which plant roots,detritus,fungi and bacteria in the soil carry out metabolic activities and consume organic matter to produce carbon dioxide.Previous studies on soil respiration under cadmium stress are mostly,but the reports on the hormetic effects induced by low-dose Cd are still insufficient,especially,the regulation of hormetic expression by exogenous addition of C,N,P and mineral ions.No reports yet.This paper took the model soil as the object,by inoculate soil microorganisms,set 8treatments:CK（control）,GC（added glucose）,NP（added nitrogen and phosphorus）,MS（enhanced by mineral ions）,GC+MS（added glucose and mineral ions at the same time）),GC+NP（simultaneous addition of glucose and nitrogen and phosphorus）,NP+MS（simultaneous addition of nitrogen and phosphorus and mineral ions）and GC+NP+MS（simultaneous addition of glucose and nitrogen,phosphorus and mineral ions）,to study the effects of glucose,nitrogen and phosphorus additions and mineral ion enhancement on soil respiration rate under Cd stress,and to simultaneously analyze the changes in soil bacterial community structure and diversity,in order to reveal the mechanism of stimulant effects in soil ecosystems and explore corresponding regulatory measures to provide theories in accordance with.The main findings and conclusions were as follows:（1）Typical hormetic phenomenons were observed in GC,NP,MS,GC+NP,NP+MS and GC+NP+MS treatments,and the maximum stimulation amplitude varied from 16.7%to 262.6%,but the occurrence time of different treatments was different.This indicated that exogenous addition of glucose,NP and mineral ions induced the expression of hormetic effects of soil respiration under Cd stress in a time-dependent manner.（2）The expression time and maximum Cd dose（range）of hormetic effects in NP,MS and GC+NP treatments were:0 h(0.04-0.1,0.4 mg·kg^-1Cd),12 h(0.02 mg·kg^-1Cd)and 48 h(0.01mg·kg^-1Cd);0 h(0.6,20.0 mg·kg^-1Cd),12 h(0.02,0.6～5.0 mg·kg^-1Cd)and 24 h(2.5mg·kg^-1Cd));0 h(0.02,0.4,2.5,13.0 mg·kg^-1Cd),12 h(0.01 mg·kg^-1Cd),and 48 h(0.01mg·kg^-1Cd).This indicated that the hormetic effects of soil respiration induced by Cd were concentrated in the initial period（0-12 h）after exposure,and a"multiple"hormetic phenomenon appeared in the dose and time series.（3）In the absence of Cd stress,the interaction of exogenous addition of glucose,NP and mineral ions on soil respiration rate were all antagonistic;the interaction of glucose and mineral ions on soil respiration was synergistic with the increase of Cd dose.Alternating with antagonism;however,for glucose and NP,the interaction between the two was shown as synergy in the0.01-0.2 mg·kg^-1dose interval and synergy and antagonism in the 0.3-30.0 mg·kg^-1dose interval.;The two treatments of NP and MS showed antagonism in the dose range of 0.02-0.3mg·kg^-1and synergy and antagonism in the dose range of 0.4-30.0 mg·kg^-1;for GC,NP and MS,the 0.01-0.6 mg·kg^-1dose range showed synergy and antagonism alternately,and the 1.0-30.0mg·kg^-1dose range showed antagonism.This indicates that in the absence of Cd stress,the microorganisms that dominate soil respiration compete for resources through antagonism regardless of exogenous addition of C sources,NPs or mineral ions.But in the presence of Cd stress,microorganisms under different addition conditions showed different interactions due to different doses and resource types.Simultaneous addition of GC,NP and MS helped reduce C loss in soil respiration under high-dose Cd stress.Only adding GC and NP might stimulate the enhancement of soil respiration under low-dose Cd stress.（4）Analysis of bacterial community structure and diversity showed that with the increase of Cd dose(0.0,1.0,20.0 mg·kg^-1),the relative abundance（RAs）of Paenibacillus community decreased significantly（P<0.05）,but this it did not lead to significant changes in bacterial community diversity index,but with the prolongation of exposure time（0,6,12,48 h）,the Shannon index of GC,MS,GC+MS,GC+NP and GC+NP+MS treatments significantly decreased（P<0.05）.（5）At the phylum level,the dominant communities of each treatment were Proteobacteria and Firmicutes,and at the genus level,the dominant community was Massilia.Addition of glucose（GC）alone or in combination with other components（GC+MS,GC+NP,GC+NP+MS）resulted in elevated RAs in Firmicutes（phylum）and Paenibacillus（genus）communities,only added MS reduced RAs in Actinobacteria（phylum）and Paenibacillus（genus）communities.（6）Correlation analysis showed that the changes of RAs in Actinobacteria（phylum）and Arthrobacter（genus）communities were significantly positively correlated with soil respiration rate（P<0.05）.Bacteroidota（phylum）as well as Pedobacter and Adhaeribacter（genus）communities also significantly affected changes in soil respiration rates with prolonged exposure time.This indicated that the changes of soil respiration rate under Cd stress were dominated by the bacterial communities of Actinobacteria（phylum）and Arthrobacter（genus）,and the exposure time（48 h）had a significant screening effect on bacterial communities.