Effects Of Microbial Inoculants On Nitrifying And Denitrifying Bacteria Community In Manure Compost

Microbial inoculants with ability of degrading lignocelluloses were added into the compost which used cow manure and rice straw as materials. Experiment was conducted to investigate the maturity of microbial inoculants compost and natural compost by measuring the temperature, p H,C/N, seed germination, NH4+-N and NO3ˉ-N content. Traditional incubation and polymerase chain reaction-denaturing gradient gel electrophoresis(PCR-DGGE) method was used to study the effects of microbial inoculants on the quantification and community diversity of nitrifying and denitrifying bacteria. It provides a theoretical basis for further understanding the role of nitrifying and denitrifying bacteria in nitrogen circulation of compost. The main conclusions are as follows:(1) The composting process lasted 45 days. These two kinds of composts both went through four phases: rapid temperature increase, sustained high temperature, gradual cooling and maturity.Maximum temperature of inoculants compost was 66℃, higher than 59℃ that is the highest natural temperature. Their high temperature stage sustained 13 days and 9 days respectively. It indicated that inoculants increased the compost temperature and extended high temperature phase.In addition, the changes of pH, C/N, seed germination NH4+-N and NO3ˉ-N value suggested that inoculating microbial agents into compost benefited microorganisms’ growth and promoted compost maturity to reach harmless standard.(2) The quantification of nitrifying bacteria in microbial inoculants compost was more than that in natural compost. However, the quantification of denitrifying bacteria was less in microbial inoculants compost. They both had a negative correlation with NH4+-N and significant positive correlation with NO3ˉ-N content(P<0.05). The correlation coefficient of inoculants compost was bigger than that of natural compost.(3) Microbial inoculants had impacts on the diversity and community structure of ammonia oxidizing bacteria with amo A gene targeted. Compared with natural compost, ammonia oxidizing bacteria species were more abundant in inoculants compost. Nitrosospira sp. was the dominant species, while the inoculants compost had some new taxas, including Nitrosovibrio sp. and Nitrosomonas sp.(4) Microbial inoculants had no significant effects on nir S type denitrifying bacteria community diversity. However, the diversities of nar G, nap A, nis K, and nos Z type were changed.Compared with natural compost, nar G gene diversity index was lower during temperature increasing stage but higher during cooling stage; Nap A and nos Z type denitrifying bacteria speciesin inoculants compost were abundant and their diversity indexs were greater than those in natural compost; Diversity of Nir K type denitrifying bacteria community decreased in inoculants compost.(5) Microbial inoculants had no influence on nir S type denitrifying population but it had great influence on nar G, nap A, nir K, and nos Z type. The dominant group of nar G type was Thiothrix sp.However, inoculants compost produced some new uncultured bacteria species, leading the quantification and proportion of bacteria classified as Thiothrix sp. reduced. Pseudomonas sp. and some uncultured bacteria were predominant genus of nap A type denitrifying bacteria in natural compost. Besides there species, microbial inoculants compost produced some new denitrifying taxas, belonged to Rhodobacter sp. and Hyphomicrobium sp. Some nir K type denitrifying bacteria detected during compost later period had high homology with group belonged to Rhodopseudomonas sp. Yet Achromobacter sp. and uncultured bacteria were not detected during natural compost cooling stage. In addition, microbial inoculants made Bradyrhizobium, Rhizobium,Bradyrhizobium, Mesorhizobium, Paracoccus, and Pseudomonas sp. disappeared but then appeared again; Nos Z type denitrifying bacteria included Achromobacter, Alcaligenes, and Pseudomonas sp. wherein Pseudomonas sp. was dominant species. In microbial inoculants compost, Halomonas, Azospirillum, Paracoccus, Herbaspirillum and Alcaligenes sp. existed but not in natural compost.