Effects of Allelochemicals, Soil Enzyme Activities, and Environmental Factors on Rhizosphere Soil Microbial Community of Stellera chamaejasme L. along a Growth-Coverage Gradient

Allelochemicals released from the root of Stellera chamaejasme L. into rhizosphere soil are an important factor for its invasion of natural grasslands. The aim of this study is to explore the interactions among allelochemicals, soil physicochemical properties, soil enzyme activities, and the rhizosphere soil microbial communities of S. chamaejasme along a growth-coverage gradient. High-throughput sequencing was used to determine the microbial composition of the rhizosphere soil sample, and high-performance liquid chromatography was used to detect allelopathic substances. The main fungal phyla in the rhizosphere soil with a growth coverage of 0% was Basidiomycetes, and the other sample plots were Ascomycetes. Proteobacteria and Acidobacteria were the dominant bacterial phyla in all sites. RDA analysis showed that neochamaejasmin B, chamaechromone, and dihydrodaphnetin B were positively correlated with Ascomycota and Glomeromycota and negatively correlated with Basidiomycota. Neochamaejasmin B and chamaechromone were positively correlated with Proteobacteria and Actinobacteria and negatively correlated with Acidobacteria and Planctomycetes. Allelochemicals, soil physicochemical properties, and enzyme activity affected the composition and diversity of the rhizosphere soil microbial community to some extent. When the growth coverage of S. chamaejasme reached the primary stage, it had the greatest impact on soil physicochemical properties and enzyme activities.

Effects of Salinity on the Biodegradation of Polycyclic Aromatic Hydrocarbons in Oilfield Soils Emphasizing Degradation Genes and Soil Enzymes

The biodegradation of organic pollutants is the main pathway for the natural dissipation and anthropogenic remediation of polycyclic aromatic hydrocarbons (PAHs) in the environment. However, in the saline soils, the PAH biodegradation could be influenced by soil salts through altering the structures of microbial communities and physiological metabolism of degradation bacteria. In the worldwide, soils from oilfields are commonly threated by both soil salinity and PAH contamination, while the influence mechanism of soil salinity on PAH biodegradation were still unclear, especially the shifts of degradation genes and soil enzyme activities. In order to explain the responses of soils and bacterial communities, analysis was conducted including soil properties, structures of bacterial community, PAH degradation genes and soil enzyme activities during a biodegradation process of PAHs in oilfield soils. The results showed that, though low soil salinity (1% NaCl, w/w) could slightly increase PAH degradation rate, the biodegradation in high salt condition (3% NaCl, w/w) were restrained significantly. The higher the soil salinity, the lower the bacterial community diversity, copy number of degradation gene and soil enzyme activity, which could be the reason for reductions of degradation rates in saline soils. Analysis of bacterial community structure showed that, the additions of NaCl increase the abundance of salt-tolerant and halophilic genera, especially in high salt treatments where the halophilic genera dominant, such as Acinetobacter and Halomonas. Picrust2 and redundancy analysis (RDA) both revealed suppression of PAH degradation genes by soil salts, which meant the decrease of degradation microbes and should be the primary cause of reduction of PAH removal. The soil enzyme activities could be indicators for microorganisms when they are facing adverse environmental conditions.

Reintroduction of Decomposed Straw To Maize Fields Resulted In Soil Microbial Community Change And Increased Corn Production

Purpose Returning decomposed straw to crop fields could address many agricultural shortcomings. In this study, the soil microbial community, soil nutrients, soil enzyme activities and maize yield were investigated after returning decomposed straw to the field. Methods To investigate the effects of returning decomposed straw to field on soil microorganisms and maize growth, field experiments were carried out to measure soil nutrient content, soil enzyme activity and maize yield, and the soil microbial community structure was measured by 16SRNA and ITS amplicon sequencing technology.Results The results showed that the contents of total nitrogen (TN), nitrate nitrogen (NN), total phosphorus (TP), available phosphorus (AP) and pH were significantly increased, and the contents of ammonium nitrogen (AN) and available kalium were decreased in both the rotary tillage (SR) and mulching (SM) treatments. The bacterial and fungal community structures in bulk and rhizosphere soils were clearly changed under SR and SM. The relative abundances of bacterial genera related to soil denitrification, such as Skermanella, Blastococcus, Geodermatophilus and Asanoa, were significantly increased. The relative abundances of Conexibacter, Streptomyces and Trichoderma, which bacteria that has shown to inhibit plant diseases, were increased. In addition, the relative abundances of growth-promoting bacteria, such as Arthrobacter and Mesorhizobium, were also significantly increased. Moreover, adding decomposed straw back to the field promoted the absorption of nutrients by maize, and resulted in higher yield of maize.Conclusions Our findings suggest positive responses of soil microbial community structure and maize growth to decomposition straw returning.

Enhancement of Interplanting of Ficus carica L. with Taxus cuspidata Sieb. et Zucc. on Growth of Two Plants

Medicinal-agroforestry systems are one of the multi-functional medicinal plant production systems, gaining attention as a sustainable alternative to traditional monoculture systems. In this study, three planting patterns were established which included: (1) monoculture F. carica (MF); (2) monoculture T. cuspidata (MT); and (3) interplanting F. carica with T. cuspidata (IFT). The differences of growth biomass, photosynthesis, soil nutrients, soil enzyme activities, soil microorganisms, and main secondary metabolites of F. carica and T. cuspidata under the above three models were investigated. Compared with the MF and MT patterns, IFT pattern for 5 months significantly increased the plant growth biomass, photosynthesis, soil organic carbon, total nitrogen, and secondary metabolites content. The activities of acid phosphatase, sucrase, protease, polyphenol oxidase, urease, dehydrogenase, and catalase in soil of IFT were significantly higher than MF and MT patterns. Results showed that IFT pattern is preferred compared to the MF and MT patterns. Our result will help to provide a feasible theoretical basis for the large-scale establishment of F. carica and T. cuspidata mixed forests and obtain high-quality medicine sources for extracting important active ingredients, psoralen and paclitaxel, which are crucial to the long-term sustainable development and production of medicinal plants.

Effect of Different Washing Solutions on Soil Enzyme Activity and Microbial Community in Agricultural Soil Severely Contaminated With Cadmium

Soil enzyme activities and microbial communities have a good response to the remediation effect of heavy metal-contaminated soils. To evaluate the effect of three commonly used washing agents, ferric chloride (FC), ethylenediamine-tetra- methylenephosphonic acid (EDTMP) and ethylenediamine tetraacetic acid (EDTA) on soil enzyme activities and microbial community in cadmium (Cd)- contaminated agricultural soil collected around the mining area. The soil enzyme activities, microbial community, chemical forms of Cd and some physicochemical properties of the soil washed with different washing solutions were determined after two months incubation. The results showed that the three washing solutions had moderate removal efficiencies (22.83%-37.56%) for Cd in the tested soil and the breakdown product of EDTMP has a certain stabilizing effect on Cd. The geometric mean and the integrated total enzyme activity index showed that soil washing with FC and EDTA were more beneficial to the restoration of biochemical functions than that with EDTMP. The relative abundance of Gemmatimonadetes in the soil washed with EDTA was significantly higher than that with FC and EDTMP. The relative abundance of Firmicutes in the soil washed with EDTMP was significantly increased, and the relative abundance of Bacteroidetes in the soil washed with FC was significantly decreased. Pearson correlation analysis and redundancy analysis (RDA) indicated that the three washing solutions affected soil enzyme activities and microbial community by altering soil nutrient, total Cd concentration and Cd fractions in soils.