Effect Of Heavy Metal Contamination On Soil Enzyme Activity And Microbial Comunities

With the rapid development of modern industry,soil heavy metal pollution has gradually become a global environmental problem.Due to the concealment and hysteresis of heavy metal pollution,it is greatly difficult to monitor and control soil heavy metal contamination.As the main driving factor of material circulation and energy flow in soil,enzymes and microorganisms play an important role in ensuring the normal operation of soil ecosystems.At the same time,they are very sensitive to changes in soil environmental conditions and can be used as important indicators to evaluate the contamination degree.Investigation on the response of soil enzymes activities and microbial cummunities during heavy metal pollution and remediation is of great significance.Lead and chromium are two heavy metals with a wide range of pollution and serious hazards.In this study,glucosidase,chitinase,phosphatase related to carbon,nitrogen and phosphorus mineralization and soil microorganisms were selected as research objects to analyze the effects of lead and chromium pollution on soil enzyme activities and microbial activities.The transformation of biochemical processes in the soil under acute and long-term heavy metal pollution was also studied.Based on this,the rhizoboxes experiment was used to investigate the fractions changes of heavy metals,the spatial and temporal distribution of enzyme activities and the response of microbial communities in the Cr contaminated soil after application with animal manure and its biochar.This study revealed the effects of lead and chromium on soil biological indicators and microbial community diversity,and provided theoretical basis and technical support for establishing early warning indicators of heavy metal pollution and bioremediation of heavy metal chromium contaminated soil.Firstly,the exogenous lead addition experiment was carried out using soils not contaminated by heavy metals,and the effect of lead pollution on soil enzyme activity was studied.The enzyme activity in forest soil and cultivated soil responds differently to lead pollution.When the lead concentration is 0¹000 mg·kg^-1,the enzyme activity is promoted in forest soil but inhibited in cultivated soil.The microbial biomass phosphorus increased firstly and then decreased with the increased lead concentration.Soil properties affect the impact of lead on soil enzymes and microorganisms.The bioavailability of heavy metals in soils with high organic matter content is weakened,and the inhibition of soil enzyme activity and microbial activity is relatively small.Secondly,a field sampling and surveying around a chemical plant in Sichuan Province was carried out.It was found that soil in this area was heavily polluted by chromium,and chromium was mainly presented in the form of organically bound and residual states.Soil organic matter content was positively correlated with the total amount of chromium,and negatively correlated with the chromium bioavailability coefficient.Soil organic matter can effectively passivate and fix chromium and reduce its bioavailability.Long-term soil chromium pollution significantly inhibits the activity of phosphatase and chitinase,and reduces the mineralization rate of nitrogen and phosphorus,which depresses the absorption and utilization of nutrients by plants,and hinders the circulation of elements and energy.Thirdly,the rhizo-box experiment was carried out by using chromium-contaminated soil collected from the chemical plant.In situ zymography technique was used to compare the spatial and temporal distribution of enzyme activity in the soil after organic fertilizer and its biochar application.Soil pH,plant biomass and chromium fraction changes under two organic matter application were investigated,and the effects of two organic matter additions on soil microbial community structure and diversity were compared.It was found that the application of manure and biochar significantly alleviated the acidification of chromium-contaminated soil,reduced the content of acid-soluble chromium,and slowed the inhibition of?-glucosidase and phosphomonoesterase by chromium pollution.The calcification effect of biochar is better than that of organic fertilizer,which significantly increases the biomass of corn stems and leaves.Meanwhile,because soil nutrients increased due to the application of organic fertilizer and biochar,the rhizosphere extent and bulk soil hotspots extent of decreased,and organic fertilizer additon decreased more.Organic fertilizer and biochar application result in a decrease in the total number of microbial species richness and eveness.The effect of organic fertilizer is stronger than that of biochar.The abundance of some strains was increased to maintain the balance of organic matter mineralization and synthetic.