Hormetic Effect Of Cd On Soil Alkaline Phosphatase

Hormesis refers to the phenomenon that the organism produces a stimulating response at low doses,but presents an inhibitory effect at high doses.The phenomenon is known as the evolution of the soil response to stress.In recent years,hormetic effect of soil ecosystem has attracted much attention.Among them,soil enzyme as the endpoint of the relevant research has become a hot issule.Land use change has a significant impact on soil properties,the components and characteristics of soil organic carbon and microbial community composition.Changes in these traits also have an important impact on the expression of hormetic effect.Recently,research on the impact of land use change on soil hormetic effect is insufficient.Therefore,it is particularly necessary to study the driving mechanism of the hormetic effect by taking soil enzymes as the end endpoint.In the Hung-tse Lake wetland nature reserve,where the environmental background is clean,the soil samples under the five land use modes of mudflat,Phragmites australis plantation,Salix babylonica plantation,Populus alba L.plantation and farmland are collected.Different doses of Cd are added externally to the soil.At the end of the test,hormetic effect of soil ALP under Cd stress was studied,and the soil physical and chemical properties,microbial community structure and diversity responses were analyzed simultaneously,and the key influence factors of hormetic effect were identified.The space-replacement time method was used to study the hormetic effect under different land use.The changes and their influencing factors,in order to provide a theoretical basis for assessing the differences in soil response to stress damage and soil quality improvement under land use change.The main research results and conclusions are as follows:（1）Under different land use types of Hung-tse lake,there is an obvious hormetic effect dose relationship between Cd and soil ALP.Under two natural covers,the maximum stimulation rate(y_max)of the hormetic effect of Cd-ALP was 8.81%and 5.84%,respectively.The dose range（D₁-D₂）of Cd induced ALP expressing hormetic effect was 0.39-3.02 mg/kg and 0.22-3.77 mg/kg,respectively.The dose range（Qi）was 7.74 and 17.14,and the potential of ALP to cope with Cd stress（R）was 11.34 and 7.85.In comparison,y_max,D₁-D₂,Qi,and R are respectively 5.22%,0.09-1.03 mg/kg,11.44 and 3.02,respectively,under the artificial land use change of farmland.It can be seen that the reclamation of Phragmites australis plantation into farmland leads to a significant decrease in y_max,Qi and R,which may lead to a decrease in the compensation potential of soil for Cd stress injury.（2）Under different land use types,Qi is mainly affected by the content of 0.1-2μm particles in the soil.The higher the particle content is,the lower the Qi is.In comparison,the soil physical and chemical properties that affect the change of R parameters are mainly pH,ion species and strength,and total nitrogen（TN）content.Among them,soil pH value and SO₄^2-content have the greatest influence on R.The change of R parameter is positively correlated with the change of soil pH,and negatively correlated with the change of SO₄^2-content.Therefore,soil texture and TN content have important effects on the expression of Hormesis effect of cd-alp under different land uses.（3）Soil organic carbon components and characteristics have a significant impact on the expression of hormetic effect.Qi is mainly affected by the content of dissolved organic carbon（DOC）in the soil.the change of R parameter has a significant negative correlation with the change of soil microbial biomass carbon（MBC）.The higher the aromaticity of soil organic carbon,the larger the R,the higher the humification index and the smaller the R.Combined with natural cover to artificial land use,the soil organic carbon aromaticity is significantly reduced and the humification index is increased.It can be considered that the wetland reclamation to the farmland and the soil compensation for Cd stress damage is reduced.（4）The number of unique OTUs of microorganisms under natural cover is significantly higher than that of artificial land use.At the level of the phylum,the dominant microbial communities（relative abundances greater than 10%）in the five land use/covering soils were Proteobacteria（30.60%-52.11%）and Acidobacteria（10.81%-14.83%）.The artificial use（farm）of natural cover（mudflat）reduced the relative abundance of Proteobacteria by 41.28%,and the relative abundance of Acidobacteria by 37.19%.In comparison,at the genus level,the dominant microbial community is Betaproteobacteria.The conversion of mudflat to farmland reduced the relative abundance of Betaproteobacteria by 39.23%.In addition,anthropogenic land use changes reduced the relative abundance of Gram-negative bacteria（G^-）and increased the relative abundance of Gram-positive bacteria（G⁺）.The proportion of soil microbial community G^-/G⁺decreased by 109.31%when natural cover was converted to anthropogenic land use.（5）There was a significant negative correlation between y_max and Chloroflexi abundance;Qi had a significant negative correlation with the relative abundance of Proteobacteria,and a positive correlation with the relative abundance of Acidobacteria and Firmicutes;R and Gemmatimonadetes abundance showed a significant negative correlation.In comparison,y_max has a significant positive correlation with G^-and Betaproteobacteria abundance,and a significant negative correlation with Chloroflexi abundance.Qi was positively correlated with Deltapopoteobacteria;negatively correlated with the abundance of Gp6 and Actinobacteria;R was positively correlated with Gammaproteobacteria.This indicates that soil microbial community characteristics,especially the relative abundance of G^-,are one of the key factors for the difference in hormetic effect under different land use/cover.