Wenjun Xie

Using Semivariogram and Moran's I Techniques to Evaluate Spatial Distribution of Soil Micronutrients

Spatial distributions of micronutrients in soils of Shouguang were evaluated using semivariogram and Morans index (Moran‘s I) techniques to compare difference and veracity of these two spatial analysis methods. A total of 601 topsoil (0–20 cm) and 155 deep subsoil (150–200 cm) samples were collected on a symmetrical grid in the regional geochemical survey of soils in Shandong Province, and copper (Cu), iron (Fe), manganese (Mn), and zinc (Zn) concentrations were analyzed and compared. The results showed significant spatial correlations of micronutrients in Shouguang soils, and the spatial correlation degree was greater in topsoil than in deep subsoil. In topsoil and deep subsoil, the spatial correlation distance for each element obtained using the semivariogram technique was 20–60 km, whereas with Morans I technique, the positive autocorrelation distance was 20–25 km and the negative autocorrelation distance was 25–55 km. The spatial autocorrelation degree was significant (P ≤ 0.05) for every micronutrient except deep subsoil Zn. Morans I technique was able to distinguish between positive and negative autocorrelations and the results of semivariogram analysis gave the sum of the positive and negative autocorrelations. This study shows that Morans I is more accurate and meaningful than semivariogram analysis for spatial autocorrelation of some soil attributes. These results provide the theoretical foundation for the application of spatial analysis methods, and Morans I in particular, in environmental research.

Pseudomonas aeruginosa L10: A Hydrocarbon-Degrading, Biosurfactant-Producing, and Plant-Growth-Promoting Endophytic Bacterium Isolated From a Reed (Phragmites australis)

Bacterial endophytes with the capacity to degrade petroleum hydrocarbons and promote plant growth may facilitate phytoremediation for the removal of petroleum hydrocarbons from contaminated soils. A hydrocarbon-degrading, biosurfactant-producing, and plant-growth-promoting endophytic bacterium, Pseudomonas aeruginosa L10, was isolated from the roots of a reed, Phragmites australis, in the Yellow River Delta, Shandong, China. P. aeruginosa L10 efficiently degraded C10–C26 n-alkanes from diesel oil, as well as common polycyclic aromatic hydrocarbons (PAHs) such as naphthalene, phenanthrene, and pyrene. In addition, P. aeruginosa L10 could produce biosurfactant, which was confirmed by the oil spreading method, and surface tension determination of inocula. Moreover, P. aeruginosa L10 had plant growth-stimulating attributes, including siderophore and indole-3-acetic acid (IAA) release, along with 1-aminocyclopropane-1-carboxylic (ACC) deaminase activity. To explore the mechanisms underlying the phenotypic traits of endophytic P. aeruginosa L10, we sequenced its complete genome. From the genome, we identified genes related to petroleum hydrocarbon degradation, such as putative genes encoding monooxygenase, dioxygenase, alcohol dehydrogenase, and aldehyde dehydrogenase. Genome annotation revealed that P. aeruginosa L10 contained a gene cluster involved in the biosynthesis of rhamnolipids, rhlABRI, which should be responsible for the observed biosurfactant activity. We also identified two clusters of genes involved in the biosynthesis of siderophore (pvcABCD and pchABCDREFG). The genome also harbored tryptophan biosynthetic genes (trpAB, trpDC, trpE, trpF, and trpG) that are responsible for IAA synthesis. Moreover, the genome contained the ACC deaminase gene essential for ACC deaminase activity. This study will facilitate applications of endophytic P. aeruginosa L10 to phytoremediation by advancing the understanding of hydrocarbon degradation, biosurfactant synthesis, and mutualistic interactions between endophytes and host plants.

Different responses to soil petroleum contamination in monocultured and mixed plant systems

The role of plant composition should be considered during ecological risk assessment of soil petroleum contamination. To evaluate the influences of plant composition on phytotoxicity, petroleum degraders, and petroleum degradation, four treatments were arranged in the present study: unplanted, bristle grass only, alfalfa only, and bristle grass and alfalfa mixed planted in uncontaminated soil or petroleum contaminated soil (w/w, 1.0%). Petroleum contamination inhibited the growth of bristle grass and alfalfa significantly, and alfalfa growth inhibition was significantly alleviated when mixed planted with bristle grass (p < 0.05). MPN analysis indicated that the mixed plant treatment can gather the benefits of two species, and facilitate the development of alkane, total hydrocarbon and PAH degraders in contaminated soil, but not occur in uncontaminated soil. Compared with alfalfa only treatment, the degradation rates for total petroleum hydrocarbons (TPH) and aliphatic fraction were significantly increased in the mixed plant treatment (p < 0.05). However, the degradation of aromatic petroleum fraction was not received substantial improvement in the mixed plant treatment, despite containing an abundant PAH degraders. Overall, mixed plant cultivation had the significant influences on plant growth, microbial community and petroleum degradation in contaminated soils. The study provides valuable insights for vegetation restoration and remediation systems in petroleum contaminated sites of study area.

Effect of Salinity on the Transformation of Wheat Straw and Microbial Communities in a Saline Soil

ABSTRACT Currently, straw transformation in saline soil is largely unknown. The effect of soil salinity on wheat straw transformation and the roles of nitrogen (N) and phosphorus (P) were evaluated in a greenhouse experiment. By sodium chloride (NaCl) addition, straw was applied at the rate of 30 g kg−1 in various saline soils (2.0–4.0 g kg−1). N or combined N and P added in straw amended saline soil (3.0 g kg−1). Three replications of each treatment were sampled to determine straw residues at 30, 60, and 90 d. Results showed straw application significantly increased microbial biomass, especially fungal biomass. Soil salinity increased by 1.0 g kg−1, which decreased straw decomposed rate by 6.3 ~ 11.1%. N application significantly increased straw decomposed rate (p < 0.05), and high salinity obviously inhibited the humidification process of straw. We suggested that straw carbon transformation regulation and little straw residue accumulation in saline soil should arouse more attentions in future studies.