| Rare earth elements were located in the IIIB.15 kinds of lanthanide elements with atomic number from 57 to 71 and Ce and Y belong to rare earth elements. In recent years, rare earth elements were widely used in agriculture, research showed that, the appropriate amount of rare earth had a certain role in promoting the growth of the organism.With the popularization and application of rare earth fertilizer, ecological and environmental problems of rare earth elements in agricultural ecosystem caused had aroused the attention of domestic and foreign scholars, but the study on residues and safety evaluation in agricultural products in the rare earth elements had been reported, and the research on the effects of rare earth elements on soil ecological environment and biological characteristics were relatively weak.Carbon and nitrogen was an important biological substance, was also the important elements of ecological system of non biological components, and the enzyme was one of the most active driving organic composition, metabolic processes of soil nutrients, purification of soil pollutants in circulation and played an important role in the. The study of soil by constant temperature culture, discussed the lanthanum on tea plantation soil carbon and nitrogen and soil urease, protease, cellulase, invertase, nitrate reductase, dehydrogenase activity under different concentrations, and the effects of soil enzyme and soil carbon and nitrogen, and provided scientific basis for the Sichuan Basin west margin area of purple soil of tea plantation rare earth ecological environment effect evaluation.(1) Effects of rare earth lanthanum has significant effects on soil organic carbon, with increasing La concentration, total organic carbon (SOC), readily oxidizable carbon (ROC), water soluble organic carbon (WSOC), microbial biomass carbon (MBC) increases first then decreases, the best promotion concentrations of lanthanum to SOCã€ROCã€WSOC and MBC were 100 mg·kg-1,both of them were significantly higher than the control; ROC, WSOC in the concentration of 300 mg·kg-1 was inhibited, SOC, MBC respectively in the concentration of 1000,800 mg·kg-1 was inhibited; the content was significantly lower than the control. With the prolongation of the culture time, SOC, WSOC and ROC had a gradually increasing trend at a low concentration(<600 mg·kg-1) but when its concentration was over 600 mg·kg-1, La3+ had a significant inhibition to them; the concentrations of MBC were decreased with the time of incubation.(2) Exogenous lanthanum on soil available nitrogen and microbial biomass nitrogen (MBN) has a significant effect. With the increase of the lanthanum concentration, soil available nitrogen, MBN presents different characteristics, the available nitrogen and MBN content increases first then decreases, the best promotion concentrations of lanthanum to soil available nitrogen and MBN were 100 mg·kg-1; the soil available nitrogen and MBN had a inhibitory effect with the increase of concentration, the inhibitory concentrations respectively were 1000 and 600 mg·kg-1. With the prolongation of the culture time, there is a difference effect of Lanthanum on soil available nitrogen and MBN, MBN content had a gradually decreased trend, the soil available nitrogen in concentrations less than 300 mg·kg-1 showed a rising trend, the concentration is over than 300 mg·kg-1 showed a downward trend.(3) Exogenous lanthanum has significant effect on soil enzyme activity. With the concentration of lanthanum increased, the urease, protease, cellulase, invertase and nitrate reductase increases first then decreases.The best promotion concentrations of lanthanum to protease were 300 mg·kg-1 and the inhibition concentration were 1000 mg·kg-1.The best promotion concentrations of lanthanum to cellulose and invertase were 300 mg·kg-1 and the inhibition concentration were 800 mg·kg-1.The best promotion concentrations of lanthanum to urease and nitrate reductase were 100 mg·kg-1 and the inhibition concentration were 800 mg·kg-1. With the prolongation of the culture time, The results showed that La3+(<600 mg·kg-1) had a positive effect on urease, protease, cellulase, invertase and nitrate reductase at a low concentration but when its concentration was 1000 mg·kg-1, La3+ had a significant inhibition to urease, protease, cellulase, invertase and nitrate reductase; the concentrations of dehydrogenase were gradually decreased with the time of incubation.(4) Correlation analysis showed that soil SOC, ROC, MBC, WSOC, MBN, available nitrogen, urease, protease and invertase, nitrate reductase, dehydrogenase, cellulase had a significant positive correlation (p<0.01); there was significant positive correlation between urease, protease and invertase, nitrate reductase, cellulose enzyme (p<0.01); there was significantly positive correlation between invertase and dehydrogenase (p<0.01); dehydrogenase had no significant correlation with the activities of urease and nitrate reductase, (P>0.05). |
