Effect Of Cd-polluted Compost On Red Soil Microbial Biomass, Enzyme And Microbial Community Diversity

Cadmium is a kind of dispensable chemical element for plant growth. It has a strong toxicity to livings. So people pay more attention to environment pollution caused by cadmium. Compost is an important fertilizer in agricultural production. The use of compost plays an important role in the aspects of offering plant nutrients and keeping soil fertilizer efficiency. Compost is regarded as a very safe fertilizer for a long time in the production of safe agricultural products as no environmental pollution food, green food and organic food. However, no pollution of compost itself is the premise of the great effect of compost. With the development of social economy and the increasing of environment pressure in recent years, the pollution of compost itself is becoming outstanding. The appearance of environmental pollution caused by unsuitable use of compost is frequent. However, because cadmium has a strong bioavailability in the soil, it is easy for plant to absorb by roots and then get into human food chain which is bad for human beings healthy. Up to now, there was few studies about heavy mental contaminated compost on red soil environmental pollution. Therefore, researches on heavy mental contaminated compost influencing on red soil properties and microbial community diversity had significant importance.In this paper, dryland red soil which was wide distributed in South China was selected in this study. Chemical analysis, sequential extraction method and PCR-DGGE were used with indoor culture condition. The effects of Cd-contaminated compost on red soil microbial biomass C,P, urease, catalase, dehydrogenase and acid phosphatase activity and the transformation of different fractions of Cd, microbial community diversity were studied in red soil. The research could provide futher information on effects of heavy metals contaminated compost on soil, and could provide a scientific reference for the production of reasonable safety compost.Chemical analysis methods was used to assess changes of microbial biomass and enzyme activities between compost and cadmium-polluted compost (8.8 mg/kg,12.8 mg/kg,17.8mg/kg,27.8 mg/kg,67.8 mg/kg,107.8 mg/kg Cd) applied to red soil. Results showed that soil microbial biomass C and P, activities of catalase, dehydrogenase and acid phosphatase decreased in all treatments during the incubation time. Compared with all treatments at the same time, Cd-polluted compost had an inhibitory effect on microbial biomass P and acid phosphatase activity than control. Microbial biomass C was activated by 0.26～98.46% in<27.8 mg/kg Cd treatment than that of control. Catalase activity was stimulated by 0.17～4.49% in treatments with< 12.8 mg/kg Cd. When treated with 8.8 mg/kg Cd, dehydrogenase activity increased by 1.6～16.1% than that of control. Urease activity increased by 0.56～65.90% with an increase of Cd in compost with<17.8 mg/kg Cd, but in treatments with> 27.8 mg/kg Cd, the urease activity was inhibited by 0.81～2.65% at the 20th day.Sequential extraction procedure and polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) analysis were used to study dynamic speciation of cadmium and changes in microbial community diversity, respectively, in red soil stressed by different concentration of cadmium-polluted compost (7.8 mg/kg,12.8 mg/kg,107.8 mg/kgCd). The resulted showed that exchangeable, carbonate, and Fe-Mn oxides fractions of Cd were higher in 12.8 mg/kg Cd and 107.8 mg/kg Cd treated (polluted) compost treatments than that in the controls. The percentage of exchangeable fraction, carbonate fraction, Fe-Mn oxides fraction were higher in Cd-contaminated compost treatments than that in the controls, they were18.49%～56.95%,18.02%～35.35%,15.04%～25.07%,respectively. The organic fraction of Cd decreased with increased Cd in compost applied to red soil. Residual formation did not change obviously in any treatment. DGGE profiles indicated that bacteria communities were affected by Cd-polluted compost to some extent. New bands (h, r, A, B, C, and D) emerged at early incubation stage, and some bands (A, B, and C) disappeared at late incubation stage. Similarity coefficient (Cs) of DGGE profiles showed that genetic similarity increased before 14 days (highest of 93.8%), and decreased after 28 days (lowest of 74.6%). High Shannon's diversity index (H) revealed activation effect of Cd to bacteria communities, which mainly attributed to the increase of carbonate fraction in 12.8 mg/kg treatment. Low H implied an inhibition of bacteria communities in 107.8 mg/kg Cd compost, which possibly due to the increase of exchangeable and carbonate fractions.In summary, soil microbial biomass C,P, urease, catalase, dehydrogenase, acid phosphtatase activity had a certain change with the incubation time after application of high Cd concentration compost to red soil. Lower than 27.8 mg/kg Cd-contaminated compost have an activation impacts on soil microbial biomass C, urease, catalase, and dehydrogenase activity. Genetic similarity increased in the early incubation stage, and decreased in the late incubation period. Bacteria communities were activated by carbonate fraction in 12.8 mg/kg Cd compost, and inhibited by exchangeable and carbonate fractions in 107.8 mg/kg Cd-contaminated compost.