[Effects of Mycorrhizal Fungi on Nitrification and Denitrification in the Rhizospheric Soil of Aquatic Plants and Its Microbial Mechanism].

To investigate the effect of mycorrhizal fungi inoculation on nitrification-denitrification in the rhizospheric soil of aquatic plants, Cyperus alternifolius and Acorus tatarinowii were inoculated with the strain MF-MD obtained from local soil. Uninoculated plants served as the control group. The plants were cultivated for 3 months under nitrogen eutrophication in water, and then the nitrification and denitrification activities in the rhizospheric soil were determined. The results showed that inoculation with MF-MD promoted nitrification in the rhizospheric soil of both plants. However, MF-MD inoculation promoted denitrification in the rhizospheric soil of Cyperus alternifolius but inhibited denitrification in the rhizospheric soil of Acorus tatarinowii. The mechanism of soil nitrification-denitrification activity was analyzed by measuring the changes in the community structure of nitrifying bacteria and denitrifying bacteria in the microbial biomass of the rhizospheric soil. It was found that the rhizospheric soil microbial biomass (SMB) of the experimental group was higher than that of the control group and that the changes in the microbial community structure related to soil nitrification and denitrification differed between groups. This study contributes to an understanding of how mycorrhizal fungi combined with aquatic plants can remove N content in eutrophic water.

[Response of Soil Respiration and Organic Carbon to Returning of Different Agricultural Straws and Its Mechanism].

Soybean, maize and rice straws were selected as raw materials to study the response of the soil respiration (SR) and soil organic carbon (SOC) to returning of different straws in the Chongming Dongtan area. The results showed that all of SR, SOC and the plant biomass of the lands with returning of different straws were higher than those of the controls. The soil with soybean straw returning possessed the lowest SR and highest SOC among the three kinds of straws, meaning its higher soil organic carbon sequestration capability than corn and maize straws returning. Straw returning significantly enhanced soil dehydrogenase, ß-glycosidase activities and microbial biomass, and soil dehydrogenase activity was significantly correlated with soil respiration. The dehydrogenase activity of the soil with soybean straw returning was the lowest, thus, the lowest SR and highest SOC. Soybean straw had the highest cellulose and lignin contents and the lowest N content among the three kinds of straws, resulting in its lowest biodegradability. Therefore, when soybean straw was returned to soil, it was difficult to degrade completely by soil microorganisms, thus the lowest soil microbial activity, eventually leading to the lowest SR and highest SOC.