Study Of Ecotoxicology Of Cr³⁺ In The Soil-corn System

Cr is one of the five toxic heavy metals in the environment. With the accelerated processof industrialization in recent years, a large amount of waste water and waste residue enteredinto agricultural soils in various ways, resulting in soil, water is seriously contaminated. Cornis one of the main food crops in our country, of which the yield and quality have direct impacton national health and sustainable development of our society. And the quality of soil directlyaffects the quality of agricultural products. The study of heavy metals in the soil-plant systemhas become a research focus in environment, agriculture, biotechnology and related fields inrecent years. Soil enzymes play an important role in the transformation of soil nutrients,energy metabolism, monitoring and restoration of contaminated soil, is considered one of theuseful biological indicators indicate whether natural or man-made pollution.In this paper, by means of indoor simulations and pot experiments, the correlationsbetween Cr³⁺and soil urease, phosphatase, arylsulfatase, dehydrogenase and catalase ofseveral major soil types in our country have been discussed. Further discuss was carried outon the change of sensitive enzymes with aging time and the impact of Cr³⁺on agronomictraits of corns, soil enzymes and microbial characteristics after the harvest of corn in potexperiments. The main conclusions are as follows:（1） Soil pH decrease with the increase of Cr³⁺adding concentration. clay and organicmatter content have a major impact on the relationship between the Cr³⁺and soil pH, the soilsamples with high clay content and organic matter, the pH fell less, and vice versa by a bigmargin.（2） Soil urease, phosohatase, arylsulphatase, catalase and dehydrogenases reachedsignificant or remarkably significant negative correlation with Cr³⁺concentrations. The modelU=A+B*C、U=A/（1+B*C） could describe the relationship better between soil enzymeactivity and Cr³⁺concentration. The activities of the five enzymes above and the enzyme totalcan all be used to characterize the degree of pollution by Cr³⁺, and the reaction mechanismwas complete inhibition （including competitive inhibition and noncompetitive inhibition）. The critical Cr³⁺concentration was25mg/kg when the soils were slightly polluted （ED10）,arylsufatase and catalase were more sensitive to Cr³⁺in acid soils, however, in alkalinen soilphosohatase and dehydrogenases were more sensitive.（3） In the aging process, soil available chromium content decreases quickly with theaging time. The Logarithmic Modal could describe the relationship better between availablechromium content and aging time. Under the same pollution concentration, the higher claycontent is and the richer organic matter is, the lower soil available chromium content is. Soilchemical behavior varied after adding Cr³⁺because of different soil pH. On the first day ofaging, the ratio of soil available chromium content to additive amount in alkaline soil waslower than that in acidic soil and in neutral soil, which indicates alkaline soil having strongerbuffering to Cr³⁺contamination.（4） When Cr³⁺was added to the soil, dehydrogenase activities fluctuant decreased withaging time at the beginning and rise up again after aging60days in alkaline soil. In neutraland acidic soil, dehydrogenase activities showed a rapid decline at the beginning and followedby a slow decline and end up with mainly stable. The inhibition rate of Cr³⁺to thearylsulfatase was higher in acidic soil than in neutral and alkaline soil. The soil arylsulfataseactivities showed a downward trend with aging time and the activities were completelyinhibited after aging90days in individual acidic soil sample.（5） Cr³⁺stress reduced the yield, ear weight, thousand seed weight, fresh straw weight ofcorn and the stress was greater on the inhibition growth of corn on the alkaline soils. Theagronomic traits of corns had remarkably significant positive correlation between each other.Path analysis showed that the order of the direct effect on the yield were as follows: earweight> thousand seed weight> fresh straw weight.（6） After the corn harvest of the pot experiments, the results of correlation analysisshowed that soil dehydrogenase, arylsulfatase, microbial biomass carbon and soil physicaland chemical properties had significant or remarkably significant correlations. This indicatesthat the microbial activity can be used as one of the indicators for monitoring soil fertility.Low concentration of Cr³⁺activates soil enzyme activity while high concentration inhibits.Cr³⁺contamination inhibits soil microbial biomass carbon and microbial quotient, whileactive the basal respiration and respiratory quotient of some soil samples.