Tian Guangming

Effect of composting process on phytotoxicity and speciation of copper, zinc and lead in sewage sludge and swine manure.

The concentration and bioavailability of heavy metals in composted organic wastes have negative environmental impacts following land application. Aerobic composting procedures were conducted to investigate the influences of selected parameters on heavy metal speciation and phytotoxicity. Results showed that both of sewage sludge (SSC) and swine manure (SMC) composting systems decreased the pH, the content of organic matter (OM) and dissolved organic carbon (DOC), and total amounts of Cu, Zn and Pb. Sequential extraction showed that readily extractible fractions of exchangeable and carbonate in Cu and Zn increased during SSC composting but decreased during SMC composting, thus their bioavailability factors (BF) enhanced in SSC but declined in SMC. The fraction of reducible iron and manganese (FeMnOX) of Cu and Zn in SSC and FeMnOX-Cu in SMC decreased, but FeMnOX-Zn in SMC gradually increased in the process of compost. In contrast, the changes of Pb distributions were similar in two organic wastes. Pb was preferentially bound to the residual fraction and its BF decreased. The evolution of heavy metal distributions and BF depended on not only total metal concentrations but also the other properties, such as pH, decomposition of OM and decline of DOC. The germination rate (RSG), root growth (RRG) and germination index (GI) of pakchoi (Brassica Chinensis L.) increased during the composting process. Linear regression analysis demonstrated that GI, which could represent phytotoxic behavior to the plants, could be poorly predicted by BF or total amount of metals, i.e., BF-Zn, T-Cu. However, the inclusion of other physicochemical parameters (pH, OM and DOC) could enhance the linear regression significances (R).

pH‐dominated niche segregation of ammonia‐oxidising microorganisms in Chinese agricultural soils

Ammonia-oxidising archaea (AOA) are increasingly recognised as the primary mediators of soil ammonia oxidation, particularly in acidic soils. To explore the niche segregation of AOA and ammonia-oxidising bacteria (AOB) and the potential effect of this segregation on nitrification rates and the nitrogen cycle in Chinese agricultural soils, AOA and AOB amoA gene databases were established, and 454 high-throughput sequencing was used to investigate the key factors leading to the niche segregation of these two types of microorganisms. qPCR results demonstrated that there were more functional genes for AOA than for AOB in most of the soils. AOA diversity was higher than AOB diversity in most of the soils with AOA operational taxonomic units (OTU) numbers ranging from 40 to 169 and AOB OTU numbers ranging from 18 to 105. pH was the most important factor influencing the community structure of AOA (P < 0.01) and AOB (P < 0.05), and acidophilic AOA (i.e. Nitrosotalea-related sequences) were dominant in soils with pH values below 6.0. In addition, AOA amoA gene copy numbers were significantly positively correlated with pH (P < 0.05), the ratio of AOA OTU numbers/AOB OTU numbers was significantly negatively correlated with pH (P < 0.05), and the percentage of sequences represented by the Nitrosotalea cluster was significantly negatively correlated with pH (P < 0.01).