A pot experiment was performed to investigate the effect of phytoremediation (CK, using tall fescue), fungi remediation (GV, using Glomus versiforme), bacterial remediation (PS, using Pseudomonas fluorescens Ps2-6), and microbial-phytoremediation (GVPS, using three species) on removing polycyclic aromatic hydrocarbons (PAHs) and the microbial diversity in soils. Inoculation with G. versiforme and P. fluorescens could increase the biomass of tall fescue and the accumulation of phenanthrene (PHE) and pyrene (PYR) in plants. Among them, the highest PHE and PYR removal efficiencies and highest biomass of tall fescue were observed in the GVPS treatment and the microbial diversity in contaminated soil was changed, the result revealed that Proteobacteria and Ascomycota were the dominant bacterial phylum and fungal phylum in all treatments, while more Proteobacteria were detected in GVPS treatment. At the genus level, the abundance of Sphingomonas (3.17%), Pseudomonas (2.05%), and Fusarium (8.65%) treated with GVPS increased compared with other treatments. These pieces of evidence contribute to a better understanding of the mechanisms involved in the combined microbial-phytoremediation strategies for PAHs-contaminated soils, especially the effects of microbial-phytoremediation on rhizosphere microbial diversity. Inoculation with G. versiforme and P. fluorescens could increase PHE and PYR removal efficiencies, the biomass of tall fescue, microbial diversity, and the abundance of Proteobacteria, Sphingomonas, Pseudomonas, and Fusarium in (PHE + PYR)-contaminated soils.

Introduction: Low temperature (LT) and weak light (WL) seriously affects the yield and quality of snapdragon in winter greenhouse. Arbuscular mycorrhizal fungi (AMF) exert positive role in regulating growth and enhancing abiotic stress tolerance in plants. Nevertheless, the molecular mechanisms by AMF improve the LT combined with WL (LTWL) tolerance in snapdragon remain mostly unknown.Methods: We compared the differences in root configuration, osmoregulatory substances, enzymatic and non-enzymatic antioxidant enzyme defense systems and transcriptome between AMF-inoculated and control groups under LT, WL, low light, and LTWL conditions.Results: Our analysis showed that inoculation with AMF effectively alleviated the inhibition caused by LTWL stress on snapdragon root development, and significantly enhanced the contents of soluble sugars, soluble proteins, proline, thereby maintaining the osmotic adjustment of snapdragon. In addition, AMF alleviated reactive oxygen species damage by elevating the contents of AsA, and GSH, and the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR), monodehydroascorbate reductase (MDHAR), and glutathione reductase (GR). RNA-seq analysis revealed that AMF regulated the expression of genes related to photosynthesis (photosystem I related proteins, photosystem II related proteins, chlorophyll a/b binding protein), active oxygen metabolism (POD, Fe-SOD, and iron/ascorbate family oxidoreductase), plant hormone synthesis (ARF5 and ARF16) and stress-related transcription factors gene (bHLH112, WRKY72, MYB86, WRKY53, WRKY6, and WRKY26) under LTWL stress.Discussion: We concluded that mycorrhizal snapdragon promotes root development and LTWL tolerance by accumulation of osmoregulatory substances, activation of enzymatic and non-enzymatic antioxidant defense systems, and induction expression of transcription factor genes and auxin synthesis related genes. This study provides a theoretical basis for AMF in promoting the production of greenhouse plants in winter.

Low-temperature and weak-light conditions have major effects on the growth and flower quality of horticultural plants. A greenhouse pot experiment was performed to investigate the effects of arbuscular mycorrhizal fungi (AMF) (Funneliformis mosseae and Glomus versiforme) on the growth, photosynthesis, and chlorophyll fluorescence parameters of snapdragon (Antirrhinum majus L.) under low-temperature and weak-light stress. The growth and biomass of snapdragon were higher following inoculation with F. mosseae and G. versiforme compared with control plants. The percentage of mycorrhizal colonization and root activity were high in A. majus plants with AMF. AMF inoculation enhanced the net photosynthetic rate, transpiration rate, stomatal conductance, and water use efficiency of plants under low-temperature and weak-light conditions. Furthermore, the chlorophyll content, potential activity of photosystem II (PSII), effective photochemistry quantum efficiency of PSII, actual photochemical quantum efficiency of PSII, and photochemical quenching coefficient were higher in AMF-inoculated plants than in uninoculated plants. The application of AMF reduced the intercellular CO2 concentration and non-photochemical quenching coefficient. Thus, snapdragon plants treated with F. mosseae and G. versiforme are more resistant to low-temperature and weak-light stress than untreated plants.

Plants in greenhouses are often exposed to low temperature and low light conditions in the winter, and this has a major effect on flower cultivation. Inoculation of plant growth-promoting rhizobacteria (PGPR) can improve the growth of plants under stress. Here, we examined the effects of Pseudomonas fluorescens on the growth, photosynthesis, chlorophyll fluorescence parameters, and antioxidant enzyme systems of violet plants (Matthiola incana) exposed to normal temperature and normal light intensity (18 °C/11 °C, 500 μmol·m^-2·s^-1, NN), low temperature and normal light intensity (4 °C/1 °C, 500 μmol·m^-2·s^-1, LN), normal temperature and low light intensity (18 °C/11°C, 100 μmol·m^-2·s^-1, NL), and low temperature and low light intensity (4 °C/1 °C, 100 μmol·m^-2·s^-1, LL). The results showed that the plant height, stem diameter, leaf area, shoot fresh/dry weight, and underground fresh/dry weight of violet inoculated with PGPR were 40%, 17%, 13%, 25%, 41%, 30%, and 38% higher than the control, respectively. In addition, the total root length, mean root diameter, number of root tips, number of bifurcated root tips, and root vigor were 24%, 23%, 14%, 30%, and 21% higher in the inoculated group than in the control group, respectively. PGPR promoted chlorophyll accumulation in plants, and the net photosynthetic rate of violets was 32% higher in plants inoculated with PGPR than in control plants. PGPR also significantly promoted the maximum photochemical conversion efficiency of photosystem II (PSII) and the potential activity of PSII under UV light. After inoculation with PGPR, the content of MDA decreased by 16.8%, and the activities of superoxide dismutase and peroxidase increased by 19.2% and 20.0%, respectively. Therefore, PGPR can promote the growth of violet plants by increasing the photosynthetic capacity, activating the antioxidant enzyme system, and reducing damage induced by exposure to low light intensity.

Perennial ryegrass is considered an excellent cold-season turfgrass, and salinity is an important environmental factor that affects its growth. Many studies have shown that arbuscular mycorrhizal (AM) fungi can alleviate stress responses in plants, but there have been few reports on the promotion of turfgrass growth in saline-alkali land by AM fungi. We designed an experiment to investigate the effects of different saline conditions (0%, 0.05%, 0.1% salt, w/w) on the growth and physiological metabolism of perennial ryegrass. The results showed that under 0.05% salt stress, AM fungi increased the plant height by 25.9%, the aboveground and underground dry weight by 37.1% and 55.6%, respectively; and the content of chlorophyll a in the plants by 31.0%. Inoculation with AM fungi increased the net photosynthetic rate (A), transpiration rate (E), intercellular CO2 concentration (Ci), and stomatal conductance (Gs) of perennial ryegrass, and the increase in their levels negatively correlated with increasing salt concentrations. Under 0.1% salt stress, the A, Ci, Gs, and E of perennial ryegrass inoculated with AM fungi increased by 24.6%, 23.2%, 139.1%, and 40.7%, respectively. However, inoculation with AM fungi reduced Fv/Fm and had no significant impacts on the SOD activity, MDA, proline (Pro) content, soluble sugar content, and soluble protein content of perennial ryegrass. In conclusion, AM fungi can promote the growth of perennial ryegrass under salt stress, enhance its photosynthetic capacity, and improve the ability of perennial ryegrass to resist salt stress.