Search

This study aimed to evaluate the suppressive potential of different soils on soybean cyst nematodes (SCN) and to estimate the suppressive mechanism. Fifteen soils (designated as soil A to O) from different agricultural fields with varying organic inputs were added with SCN-infested soil and grown with a green soybean variety. The SCN density in the soil at 6 weeks of soybean growth was markedly different depending on the soils used, indicating a different level of disease suppressiveness. No significant correlation was observed between the SCN density and any of the soil physicochemical and biological characteristics tested. Then, to estimate a suppression mechanism, F-soil that showed the lowest density of SCN was added to the SCN-infested soil with or without streptomycin to kill bacteria and grown with soybean. SCN density was not increased by the addition of streptomycin, indicating that soil bacteria may not be involved in the suppressiveness of F-soil. In total, 128 fungal strains were isolated from the rhizosphere of F-soil and inoculated in a combination or singly in the SCN-infested soil. After repeated screenings, five strains were selected since the SCN density was consistently decreased by them. Sequence analysis showed that they were closest to Clonostachys rosea, Aspergillus niger, Aspergillus fumigatus, Fusarium oxysporum, and Cylindrodendrum alicantinum. All five strains significantly reduced the mobility of second-stage juveniles (J2). Further, C. rosea a2, A. niger a8, and F. oxysporum a25 significantly decreased hatching. Overall, the present study demonstrated that soil fungi played an important role in SCN suppression in F-soil.

Long-term fertilization can result in changes in the nitrogen (N) cycle in maize rhizosphere soil. However, there have been few reports on the impacts of plant–soil–microbe regulatory mechanisms on the N cycle in soil. In this study, soil samples were collected from a long-term experimental site located at Jilin Agricultural University, Changchun City, Jilin Province, Northeast China. We then analyzed the changes in the functional genes related to the N cycle, soil enzyme activity, and maize root exudates under long-term fertilizer application using metagenomics and liquid chromatography analysis. We aimed to investigate the response of the N cycle to long-term fertilizers, the interaction among plant, soil, and microbes, and the effect of the plant–soil–microbe system on the N cycle. Long-term fertilization had a significant effect on soil N contents, N2O emissions, and enzyme activity related to the N cycle in maize rhizosphere soil. The functional genes of the N cycle were mainly enriched in the N degradation pathway in maize rhizosphere soil. N fertilizer application decreased the abundance of functional genes related to N fixation and degradation, denitrification, and assimilatory nitrate reduction (ANRA) and increased the abundance of functional genes participating in dissimilatory nitrate reduction (DNRA) and anaerobic ammonia oxidation/hydroxylamine oxidation. The soil environment was positively related to soil enzyme activity and negatively related to the microbial community composition and amino acids in root exudates. The contribution rate of microorganisms to the N cycle was the highest (r2 = 0.900), followed by amino acids (r2 = 0.836) and the soil environment (r2 = 0.832). Therefore, we concluded that N fertilizer is the main factor limiting the soil N cycle and that microorganisms are the main factor regulating the N cycle in the plant–soil–microorganism system.

Changbai Mountain is an important part of the development and opening pilot area of Changjitu. It is the birthplace of Songhua River, Yalu River, and Tumen River, and is known as the source of the three rivers. Millions of people live in the basin. A volcanic eruption accompanied by earthquakes would lead to a large number of landslides, debris flows, and show a chain effect, the formation of a secondary geological disaster chain, which is a serious threat to people’s lives and property safety. This paper selected indexes from three aspects: the hazard of earthquake-induced geological disaster chain, the exposure and vulnerability of disaster-bearing bodies, and the risk assessment of earthquake-induced geological disaster chain. The sensitivity values of each influence factor were calculated by the certainty factor (CF) using the support vector machine, and then, the susceptibility assessment was obtained. The cumulative displacement calculated by the Newmark model represented the potential risk intensity. We considered the Changbai Mountain volcanic earthquake–landslide disaster chain as an example. The results of risk assessment showed that the extremely high and high risk areas were mainly located within the 12 km radius of Tianchi Lake, and the other areas in the study area were mainly associated with very low to low risk values. The verification results showed that the receiver operating characteristic (ROC) curve area was 0.8373, indicating that the method was very effective in the identification and assessment of seismic hazard chain risk. In these high-risk areas, relevant countermeasures should be formulated to prevent the risk of geological disasters, strengthen the implementation of regional disaster prevention and reduction work, and ensure the safety of residents’ lives and property.