Effects of Carbon and Nitrogen Additions on Soil Microbial Biomass Carbon and Enzyme Activities Under Rice Straw Returning

The effects of different amounts of carbon and nitrogen sources on the soil microbial biomass carbon,dissolved organic carbon and related enzyme activities were studied by the simulation experiment of rice straw returning to the field,and the mechanism of the decomposition of rice straw returning to the field was discussed.Completely randomized experiment of the two factors of the three levels was designed,and a total of nine treatments of indoor soil incubation tests were conducted.Full amount of rice straw was applied to the soil in this simulation experiment and different amounts of brown sugar and urea were added in the three levels of 0(no carbon source and nitrogen source),1(low levels of carbon and nitrogen sources)and 2(high levels of carbon and nitrogen sources),respectively.The results showed that the addition of different amounts of carbon and nitrogen sources to the rice straw could increase the soil carbon content.Compared with T0N0,the microbial biomass carbon of T2N2 was increased significantly by 170.48%;the dissolved organic carbon content of T1N2 was significantly increased by 58.14%and the free humic acid carbon contents of T0N2,T1N1 and T2N0 were significantly increased by 56.16%and 45.55%and 47.80%,respectively;however,there were no significant differences among those of treatments at later incubation periods.The addition of different carbon and nitrogen sources could promote the soil enzyme activities.During the incubation period,all of the soil enzyme activities of adding sugar and urea were higher than those of T0N0 treatment.Therefore,the addition of different amounts of carbon and nitrogen sources to rice straw returning could improve soil microbial biomass carbon content,dissolved organic carbon and soil enzyme activities.

Characteristics and Culture Conditions of a Bioflocculant Produced by Penicillium sp.

Objective To study the characteristics of a bioflocculant named MBF7 produced by Penicillum strain HHE-P7 and the effects of cultivation conditions on bioflocculant production. Methods The chemical group in the bioflocculant molecules was shown by Fourier transform infrared （FTIR） spectra, and the average molecular weight of MBF7 was estimated by gel permeation chromatography. The effects of medium components on bioflocculant production and flocculating activity were studied. Results Phospho-, amino-, hydroxyl, and carboxyl groups were the major fractions of MBF7, and the molecule weight was about 3.0 × 10^5 Da. In addition, the carbon and nitrogen sources favorable for the bioflocculant production were glucose and yeast extract respectively. When the initial pH of the medium was adjusted to 5.0, high flocculant efficiency could be achieved. Conclusion The bioflocculant MBF7 is a new macromolecule with high flocculating efficiency for Kaolin suspension, and could be produced under appropriate culture conditions.

Enhancement of Laccase Activity by Marine-derived Deuteromycete Pestalotiopsis sp. J63 with Agricultural Residues and Inducers

Pestalotiopsis sp. J63, producing a high activity of laccase, is a new marine-derived fungus isolated from the oceanic sediment of the East China Sea. Since the marine environment is oligotrophic nutrient, marine derived fungi may use small amount of nutrients to grow and produce laccases. Agricultural residues that are mainly composed of lignin, cellulose and hemicellulose are difficult to be degraded and few microbes can take them as substrates, so they are considered as oligotrophic nutrient and have the potential to be used to produce value added products. In this study, the ability of Pestalotiopsis sp. J63 to use agricultural residues to produce laccases was tested in the submerged fermentation. The combination of 3 g·L 1maltose and 20 g·L 1rice straw was the best carbon sources and 8 g·L 1ammonium sulfate was the best nitrogen source under the condition without inducers. The effects of five inducers, the feeding time and concentration of inducer on laccase production were investigated.Adding 0.09 mmol·L 1phenol after 24 h of incubation led to high laccase activity(5089 U·L 1), while with 0.09mmol·L 1phenol in the medium and wheat bran as the nitrogen source, the laccase activity could reach 5791.7U·L 1. Native-PAGE results showed that two laccase isozymes were present in the cultures. One existed in both induced and non-induced culture filtrates, while the other was only found in the fermentation with the addition of phenol, guaiacol and veratryl alcohol.