Profiles of antibiotic resistome with animal manure application in black soils of northeast China.

Black soils (Mollisols) are important soil resources for crop production and maintain food safety in China. For keeping soil fertility, the application of animal manure is commonly practiced in black soils. However, the impact of this application on abundance and diversity of antibiotic resistance genes (ARGs) in black soils of China remains unclear. Here, we surveyed the profiles of ARGs in 72 soil samples collected from four long-term experimental stations with different fertilization regimes and from open farmlands in two sites across northeast China using high-throughput quantitative PCR. Results showed that a total of 178 ARGs including mobile genetic elements (MGEs) were detected, and the diversity and abundance of ARGs were significantly increased with manure application. Additionally, the finding of a significant positive correlation between relative abundance of ARGs and MGEs (P < 0.0001), suggesting that horizontal gene transfer may potentially impact the transmission of ARGs. Furthermore, two genes aadA-1-01 and mexF, encoding resistance to aminoglycoside and multidrug, respectively, were recognized as indicators to estimate the abundance of other co-occurring ARGs. These findings provided insights into the soil resistome in black soils of northeast China and also highlighted the environmental risks caused by manure application should not be ignored.

[Comparison on fungal molecular ecological networks of agricultural soils with different latitudes in the black soil region of Northeast China]. / 东北黑土区不同纬度农田土壤真菌分子生态网络比较.

To investigate the differences of fungal network structures and interaction among fungal species of in black soil region of Northeast China, Illumina MiSeq sequencing was used to reveal the fungal communities in the three long-term fertilization experimental fields. Fungal molecular ecological networks were constructed based on random matrix theory (RMT). The results demonstrated that Ascomycota, Basidiomycota and Zygomycota were the dominant phyla and Hypocreales, Pleosporales and Sordariales were the dominant order, but the relative abundance of some dominant taxa significantly varied in different locations. Fungal molecular ecological network structures in three locations showed significant difference, with more complex fungal network being observed in north location with more competitive relations among species. The fungal network in south location was more easily disturbed by environmental perturbations with less stability. Only seven shared nodes were detected among three fungal molecular ecological networks. There were large differences in connectivity of shared nodes within individual fungal network. The subnetwork of Hypocreales was gradual complex from south to north location while subnetwork of Pleosporales presented reversed trend. The key species of south, middle and north locations were Chaetomiaceae, Pleosporales and Penicillium coralligerum, respectively. Soil pH and total N content were the main soil properties simultaneously influencing three fungal networks.

Impacts of organic and inorganic fertilizers on nitrification in a cold climate soil are linked to the bacterial ammonia oxidizer community.

The microbiology underpinning soil nitrogen cycling in northeast China remains poorly understood. These agricultural systems are typified by widely contrasting temperature, ranging from -40 to 38°C. In a long-term site in this region, the impacts of mineral and organic fertilizer amendments on potential nitrification rate (PNR) were determined. PNR was found to be suppressed by long-term mineral fertilizer treatment but enhanced by manure treatment. The abundance and structure of ammonia-oxidizing bacterial (AOB) and archaeal (AOA) communities were assessed using quantitative polymerase chain reaction and denaturing gradient gel electrophoresis techniques. The abundance of AOA was reduced by all fertilizer treatments, while the opposite response was measured for AOB, leading to a six- to 60-fold reduction in AOA/AOB ratio. The community structure of AOA exhibited little variation across fertilization treatments, whereas the structure of the AOB community was highly responsive. PNR was correlated with community structure of AOB rather than that of AOA. Variation in the community structure of AOB was linked to soil pH, total carbon, and nitrogen contents induced by different long-term fertilization regimes. The results suggest that manure amendment establishes conditions which select for an AOB community type which recovers mineral fertilizer-suppressed soil nitrification.

[Effects of different long-term fertilizations on community properties and functions of methanotrophs in dark brown soil].

The microbial mechanisms of how different long-term fertilizations change methane oxidation of Chinese upland arable soil is unclear so far. In the present study, we attempted to investigate the "soil properties-community properties of methanotrophs-methane oxidation" relation of dark brown soil in Northeastern China under different long-term fertilization regimes. Community structure and abundance were monitored with PCR-DGGE and real time PCR, respectively. Methane oxidizing rate and soil properties were measured as well. The results show that combined use of mineral fertilizer and compost (MNP) reduce soil methane oxidation by 61.2%, whereas either mineral fertilizer (NP) or compost (M) shows no effect. Comparing with no fertilizer (CK), M and MNP increase the Shannon index of methanotrophs by 91.9% and 102.5%, respectively, whereas NP has no effect. Similarly, M ( M or MNP) significantly increases pmoA gene abundance by up to 12.7 folds compared with no M addition (CK or NP). Methane oxidizing rates are significantly correlated with community structure and specific activity of methanotrophs, with correlation coefficients of 0.363 and 0.684, respectively. However, methane oxidizing rates do not correlate with abundance and diversity of methanotrophs. In addition, community structures and specific activity of methanotrophs are significantly correlated with soil pH and content of total nitrogen and organic matter. Our results suggest that long-term different fertilizations may change soil properties (such as pH and content of total nitrogen and organic matter) and thereafter the community structure and specific activity of soil methanotrophs, by which long-term different fertilizations influence soil methane oxidizing rate. The opposite change of methane oxidation to methanotrophs diversity and abundance in MNP suggests that only parts of the methanotrophs are active, which needs further research.