Effect Of Heavy Metal Pollution On Soil Respiration And Microbial Community Structure In Paddy Soils

Paddy field is an important agricultural ecosystem in China.Heavy metal pollution of paddy soils has become increasingly serious for recent decades due to pollution from mining and metallurgical industry,extensive application of sewage irrigation,sewage sludge land disposal as well as from pesticides and fertilizers in crop production.Pollution of heavy metals in paddy soils may induce changes in soil microbial biomass,microbial community structure and functioning activity and,in turn,soil respiration and greenhouse gas emission from soils.At present,many studies of effect of heavy metal pollution on soil microbial activity have been conducted under spiked treatments or using lab incubation of field soils while it's quite different from the field condition.The impact of heavy metal pollution on changes in soil microbe and soil respiration from rice paddies had not been reported yet.In this thesis,topsoil samples from polluted paddy soils from Fuyang county of Zhejiang province and Yixing county of southern Jiangsu,China were collected.Soil microbial biomass carbon and soil respiration were measured in conjunction with a community structure analysis using analysis of phosphorus-lipid fatty acids(PLFA).The main results in the study were as follows:1.Soil microbial biomass carbon and nitrogen decreased significantly under the heavy metals pollution of Cd,Pb and Cu.The soil respiration rate increased by 2.52 to 4.25 mgCO₂-C·kg^-1OC·d^-1.The qCO₂ also increased significantly.Therefore,heavy metal pollution might raise the metabolism of soil microbes thus increase increase greenhouse gas emissions from rice fields.2.Soil microbial community structure and composition changed under the heavy metal pollutions.PLFA analysis showed a remarkable reduction(30%) of the ratio of fungi PLFA. The ratio of fungi/bacterial decreased by about 70 percent.The ratio of fatty acid between gram-positive bacteria and gram-negative bacteria increased.Heavy metal pollution lead to a increase of gram-positive bacteria and anaerobic microbial groups and a decrease of gram-negative and aerobic microorganisms in the soil.