Effect Of Rare Earth Element Lanthanum On Microflora In Chao Soil

LaCl₃ solution was added into yellow soil at different levels: 0mg·Kg^-1,10mg·Kg^-1, 50mg·Kg^-1,100mg·Kg^-1, 200mg·Kg^-1,300mg·Kg^-1, 500mg·Kg^-1,1000mg·Kg¹,1500mg·Kg^-1, 2000mg·Kg^-1.Water was added for retaining soil moisture, the soils were sampledfor the determination of La effects every week.The CFU (colony forming units) of bacteria increased with increasing concentra-tion of La, and there was a maximum increase ratio of 53.26% at La concentration of200mg·Kg^-1, and was inhibited mostly during the whole incubation when La concen-tration was 2000mg·Kg^-1 by 11.96%. The CFU of fungus increased while theconcentration of La below 500 mg·Kg^-1, and there was a maximum increase ratio of27.19% at La concentration of 200mg·Kg^-1, and was inhibited mostly during thewhole incubation when La concentration was 2000mg·Kg^-1 by 39.19%. La had nosignificant effect on the CFU of actinomyces while the concentration below50mg·Kg^-1, the maximum increase was when the concentration of La was 100mg·Kg^-1, and the inhibit ion became significant when the concentration of La wasover 200mg·Kg^-1, and was inhibited mostly during the whole incubation when Laconcentration was 2000mg·Kg^-1 by 70.82%.The number of soil ammonifiers bacteria was decreased half while the concentra-tion of La was 50mg·Kg^-1, and there was a maximum increase ratio of 55.05% at Laconcentration of 300mg·Kg^-1.While La below stimulated the growth of nitrier bacteria,the total population of nitrier bacteria increased by 3.08 times. When La was accumul-ated above 200 mg·Kg^-1, the total population of nitrier bacteria descend. La inhibitedthe growth of azotobacter, and La had no significant effect on the population ofazotobacter while the concentration below 500mg·Kg^-1, but its higher concentrationhas inhibitory effect. The growth of cellulose-decomposing bacteria was stimulatedwhen the concentration of La was below 200mg·Kg^-1, the total population ofcellulose-decomposing bacteria increased by 53.49%. When La was accumulatedabove 500 mg·Kg^-1, the total population of cellulose-decomposing bacteria descend.The effect on soil urease was not as significant. The activity of protease increasedwhile the concentration of La below 1500mg·Kg^-1, and was a maximum increase ratio of 52.63% at La concentration of 200mg·Kg^-1. At the concentration of 2000mg·Kg^-1the activity of protease descend but not significant. When the incubation is prolonged,there is a tendency of decreasing in the effects of La on soil catalase activity. At theconcentration of 100mg·Kg^-1 the activity of catalase descend significantly, anddescend by 58.65% while the concentration of La was 500mg·Kg^-1.The sensitivity of the 3 major microbial types to La was in a decreasing order ofactinomyces>fungus>bacteria. Among the 4 soil microbial physiological groups,theorder of sensitivity to La was: cellulose-decomposing>nitrier bacteria>ammonifi-ers,azotobacter. The effect of La on 3 kinds of soil enzymes had a sensibility orderfrom top to bottom: protease, catalase, urease.Most of the soil microorganism can not be cultured now, so we used PCR-DGGEto study the soil samples in order to get the information of uncultured microorganismand anticipate to understand more about the effect of La for soil ecology.Through the results of DGGE we can get that the number and brightness of thebands changed remarkably after the disposal of La. It reflected the changes of soilmicroflora, espically the growth of the bacteria that can degrade or tolerant to La. Weused the Quantitive one soft to analyze the picture of DGGE. We can get that thesimilarity between low concentration is high, the similarity between high concentra-tion is low, the similarity between the low and high concentration is low. So we canconclude that La has great effects on soil microflora, with the concentration increa- se,the effect became bigger. And the results are similar with the conclusion of the CFUresults.