ABSTRACT Biochar soil amendments are attracting attention as one strategy to improve soil microbially ecological environment and regulate the soil nitrogen cycle. This study aimed to evaluate the effects of biochar application on agricultural soil improvement, nitrogen (N) mineralization and nitrification. The experiment was carried out on a typical farmland containing black soil and saline-alkaline soil in Northeast China. Four treatments were undertaken, including the control-treated black soil farmland (CS), the biochar-treated black soil farmland (BCS), the control-treated saline-alkali soil farmland (SAS), and the biochar-treated saline-alkaline soil farmland (BSAS). Basic physical and chemical properties, enzyme activity, and the contents of ammonium-nitrogen (NH4+-N) and nitrate-nitrogen (NO3--N) in the soil were subsequently determined. The co-occurrence networks of bacterial communities of the biochar and control treatment groups were constructed based on high-throughput sequencing data of the 16S rRNA genes. The results showed that the BCS and BSAS treatments significantly increased the contents of soil organic matter, total nitrogen, total phosphorus, and available phosphorus. The application of biochar significantly increased the NH4+-N contents in the black soil and saline-alkaline soil by 81.78 and 80.08 %, respectively, while significantly reducing the soil NH4+-N/NO3--N content, which promoted the transformation of NH4+-N into NO3--N. Subsequently, the released NH4+-N was transformed into NO3--N through nitrification. After the biochar application, the NO3--N contents in the black and saline-alkaline soils could be fixed. The biochar application significantly increased the abundance of gdh, AOA-amoA, AOB-amoA, nirK, nirS, nosZ, and nifH genes, with no significant difference in the abundance of napA genes being found among different treatments. Microbes playing a key role in the co-occurrence network were Proteobateria, Acidobacteria, Bacteroidetes, Actinobacteria, and Chloroflexi. As compared with the CS and SAS treatments, under the BCS+BSAS treatment, the connectors, module hubs, connectedness, and clustering coefficient showed larger parameters, and the networks were more complex. The application of biochar gradually increased the nodes, edges, and average degree of the bacterial co-occurrence network, thus indicating that the interaction between microbial groups in the black and saline-alkaline soils post biochar application may be important in the biogeochemical cycle process in farmland soil.

ABSTRACT Biolog Eco technology was used to investigate the effects of different chemical herbicide application methods, such as pre-emergence after sowing and post-emergence (stem and leaf spraying), on the characteristics of carbon source utilization by microbial communities in alfalfa rhizosphere soil. The averages of well color development (AWCD) and microbial metabolism diversity indices of post-emergence herbicide spraying on stems and leaves were significantly lower than those of pre-emergence herbicide and without herbicide treatments. Furthermore, pre-emergence after sowing herbicide treatment did not affect soil microorganisms. The principal component analysis (PCA) revealed that the microbial community diversities of the rhizosphere soils differed significantly between herbicide treatments. Carbohydrate was the carbon source type that was most sensitive to herbicide treatment changes, followed by amino acids and carboxylic acids. The herbicide application method significantly reduced the capacities of the microbial community to utilize the carbon sources, as mainly manifested in the ability to use polymers. As shown by a comprehensive analysis on the growth of alfalfa and the physiological and biochemical indices of its root system, the application of herbicide chlorimuron-ethyl reduced the alfalfa yield, and the two different application methods tested showed no significant difference. Herbicide application and different application methods showed significant impacts on alfalfa root activity and membrane permeability, suggesting that the application of herbicide damaged the membrane permeability and the activity of the alfalfa root system. Impacts of herbicide residues in the soil after stem and leaf post-emergence treatment on alfalfa growth and soil microorganisms should not be ignored.

ABSTRACT To reveal the differences between land-use patterns and the changes in soil properties, the changes in soil bacterial microbial communities and functions driven by land-use patterns were studied by 16SrRNA Gene Fragments and its high-throughput sequencing, relying on the wetland, farmland and forestland soils in the Hongxing National Nature Reserve of Heilongjiang Province. The study area was slightly acidic soil, and the water content, soil organic carbon content, total soil nitrogen and phosphorus contents of wetland soil were higher than farmland and forestland. The suitable C/N of wetland and farmland soil could promote the decomposition of organic matter by microorganisms. The OTUs sequence, Shannon diversity index, ACE index and Chao1 index were significantly higher in wetland than in farmland and forestland. Proteobacteria, Acidobacteria, Bacteroidetes and Actinobacteria were the dominant bacteria in the tested soil samples. The abundance of Proteobacteria in wetland soil samples was significantly higher than in farmland and forestland. The abundance of Acidobacteria in farmland soil samples was significantly higher than in wetland and forestland. According to FAPROTAX algorithm and BugBase phenotype analysis, land-uses can change the abundance of soil functional microorganisms. The dominant functional genes are mainly Chemoheterotrophy and Aerobic chemoheterotrophy bacteria. Nitrification and Aerobic ammonia oxidation bacteria involved in nitrogen cycle in farmland soil are significantly different from wetland and forestland. Land-use mode leads to significant differences between Mobile elements and Gram negative bacteria. It is mainly related to the changes in soil physical and chemical properties such as soil pH, bulk density, soil organic carbon and total nitrogen contents.