Introduction: Microbes play key roles in maintaining soil ecological functions. Petroleum hydrocarbon contamination is expected to affect microbial ecological characteristics and the ecological services they provide. In this study, the multifunctionalities of contaminated and uncontaminated soils in an aged petroleum hydrocarbon-contaminated field and their correlation with soil microbial characteristics were analyzed to explore the effect of petroleum hydrocarbons on soil microbes.Methods: Soil physicochemical parameters were determined to calculate soil multifunctionalities. In addition, 16S high-throughput sequencing technology and bioinformation analysis were used to explore microbial characteristics.Results: The results indicated that high concentrations of petroleum hydrocarbons (565–3,613 mg•kg⁻¹, high contamination) reduced soil multifunctionality, while low concentrations of petroleum hydrocarbons (13–408 mg•kg⁻¹, light contamination) might increase soil multifunctionality. In addition, light petroleum hydrocarbon contamination increased the richness and evenness of microbial community (p < 0.01), enhanced the microbial interactions and widened the niche breadth of keystone genus, while high petroleum hydrocarbon contamination reduced the richness of the microbial community (p < 0.05), simplified the microbial co-occurrence network, and increased the niche overlap of keystone genus.Conclusion: Our study demonstrates that light petroleum hydrocarbon contamination has a certain improvement effect on soil multifunctionalities and microbial characteristics. While high contamination shows an inhibitory effect on soil multifunctionalities and microbial characteristics, which has significance for the protection and management of petroleum hydrocarbon-contaminated soil.

In this study, the short-term effects of NaCl stress on the free amino acid content and composition of root exudates of Phragmites australis were evaluated. Nineteen amino acid types were detected in all samples. The results indicated that NaCl significantly influenced the total amino acid (TotAA) content. The TotAA content at 6‰ salinity (1098.79 μM g⁻¹ DW) was up to 24 times higher than that in the control group (45.97 μM g⁻¹ DW) but decreased to 106.32 μM g⁻¹ DW at 6‰ salinity in the first hour. The stress period also significantly affected the TotAA content. After 4 h of stress, the TotAA content of the control and 1‰ salinity groups increased by approximately 30- and 14-fold, and those of the 3‰ and 6‰ groups decreased to 60% and 37%, respectively. The increase in TotAA content was primarily caused by the increase in proline content; the proportion of proline accounted for 58.05% of the TotAA content at 3‰ salinity level in 2 h. Most amino acids showed a significant positive correlation with each other, but proline and methionine showed a different trend. Therefore, the proline level is a useful indicator of salt stress in Phragmites australis, especially in saltwater wetlands.

Using molecular biology methods (qualitative and quantitative PCR ), we determined the occurrence and abundance of ammonia‐oxidizing archaea ( AOA ) and ammonia‐oxidizing bacteria ( AOB ) from a dry inland soil in Basel, Switzerland, and from the riparian zone of Baiyangdian Lake, China. We also determined the contributions of these microorganisms to ammonia oxidization at different depths based on the nitrification rate. The number of archaeal amo A genes (the key functional gene in AOA ) was larger than the number of bacterial amo A genes in each sample, suggesting a dominant role for the AOA amo A gene in environments with a low ammonium concentration. In Baiyangdian Lake, the number of archaeal amo A genes was highest at 6 m and lowest at 12 m from the land–water interface in the soil (at depths from 40 to 60 cm), close to the groundwater, which suggests that AOA become more competitive in environments with a low dissolved oxygen content and are promoted by low pH . The nitrification rate was significantly negatively correlated with depth in the Baiyangdian Lake soil and significantly positively correlated with the number of AOB amo A genes at this site, 6 m from the water.