With global warming, drought has become one of the major environmental pressures that threaten the development of global agricultural and forestry production. Cenococcum geophilum (C. geophilum) is one of the most common ectomycorrhizal fungi in nature, which can form mycorrhiza with a large variety of host trees of more than 200 tree species from 40 genera of both angiosperms and gymnosperms. In this study, six C. geophilum strains with different drought tolerance were selected to analyze their molecular responses to drought stress with treatment of 10% polyethylene glycol. Our results showed that drought-sensitive strains absorbed Na and K ions to regulate osmotic pressure and up-regulated peroxisome pathway genes to promote the activity of antioxidant enzymes to alleviate drought stress. However, drought-tolerant strains responded to drought stress by up-regulating the functional genes involved in the ubiquinone and other terpenoid-quinone biosynthesis and sphingolipid metabolism pathways. The results provided a foundation for studying the mechanism of C. geophilum response to drought stress.

Cadmium (Cd) displays strong toxicity, high mobility, and cannot be degraded, which poses a serious threat to the environment. Cenococcum geophilum (C. geophilum) is one of the most common ectomycorrhizal fungi (ECMF) in the natural environment. In this study, three Cd sensitive and three Cd tolerant strains of C. geophilum were used to analyze the physiological and molecular responses to Cd exposure. The results showed that Cd inhibited the growth of all strains of C. geophilum but had a less toxic effect on the tolerant strains, which may be correlated to a lower content of Cd and higher activity of antioxidant enzymes in the mycelia of tolerant strains. Comparative transcriptomic analysis was used to identify differentially expressed genes (DEGs) of four selected C. geophilum strains after 2 mg/L Cd treatment. The results showed that the defense response of C. geophilum strain to Cd may be closely related to the differential expression of functional genes involved in cell membrane ion transport, macromolecular compound metabolism, and redox pathways. The results were further confirmed by RT-qPCR analysis. Collectively, this study provides useful information for elucidation of the Cd tolerance mechanism of ECMF.

MYB transcription factors have a wide range of functions in plant growth, hormone signaling, salt, and drought tolerances. In this study, two homologous transcription factors, PtrMYB55 and PtrMYB121, were isolated and their functions were elucidated. Tissue expression analysis revealed that PtrMYB55 and PtrMYB121 had a similar expression pattern, which had the highest expression in stems. Their expression continuously increased with the growth of poplar, and the expression of PtrMYB121 was significantly upregulated in the process. The full length of PtrMYB121 was 1395 bp, and encoded protein contained 464 amino acids including conserved R2 and R3 MYB domains. We overexpressed PtrMYB121 in Arabidopsis thaliana, and the transgenic lines had the wider xylem as compared with wild-type Arabidopsis. The contents of cellulose and lignin were obviously higher than those in wild-type materials, but there was no significant change in hemicellulose. Quantitative real-time PCR demonstrated that the key enzyme genes regulating the synthesis of lignin and cellulose were significantly upregulated in the transgenic lines. Furthermore, the effector-reporter experiment confirmed that PtrMYB121 bound directly to the promoters of genes relating to the synthesis of lignin and cellulose. These results suggest that PtrMYB121 may positively regulate the formation of secondary cell wall by promoting the synthesis of lignin and cellulose.

Nowadays, biochar is increasingly used widely as an important soil amendment to enhance soil nutrients availability. Therefore, we investigated the effect of C.oleifera shell biochar (CSB) on C.oleifera plantation soils to provide evidence that C. oleifera shell as a raw material in biochar has great potential to be a soil amendment. For this, a short-term incubation experiment was conducted in controlled conditions to evaluate the effects of CSB application on two soil chemical properties, microbial biomass, and enzymatic activity. We compared two acidic soils, mixed with CSB of three pyrolysis temperatures (300, 500, and 700 °C), and two application rates (3% and 5% (w/w)), incubated for 180 days. The results showed that the soil pH, total P (TP), and available P (AP) significantly increased under 5CSB700 in two soils, and indicated CSB application rate and pyrolysis temperature had a significant impact on soil pH, TP, and AP (p < 0.05). CSB application also significantly increased the total inorganic P in two soils and presented a significantly positive correlation with soil pH, TP, and AP under redundancy analysis. The results suggested that CSB application has a variable effect on soil enzymatic activity, microbial biomass C (MBC), and microbial biomass P (MBP) on average, while it increased the soil microbial biomass N (MBN) in both soils. We concluded that CSB could be a soil amendment to increase soil nutrients of C.oleifera plantation soils. Before the application of biochar to C.oleifera plantation forest soils, long-term studies are required to assess the effects of biochar under field conditions and its promoting effect on the growth of C. oleifera.

Escherichia coli O157:H7 is a well-recognized cause of human illness. Survival of Escherichia coli O157:H7 in five purple soils from Sichuan Province was investigated. The dynamics of E. coli O157:H7 survival in purple soils were described by the Weibull model. Results showed that this model is suitable to fit survival curves of E. coli O157:H7 in purple soils, with the calculated t_d value (survival time needed to reach the detection limit of 100 CFU·g⁻¹) ranging from 2.99 days to 26.36 days. The longest survival time of E. coli O157:H7 was observed in neutral purple soils (24.49 days), followed by alkalescent purple soil (18.62 days) and acid purple soil (3.48 days). The redundancy analysis (RDA) revealed that t_d values were significantly enhanced by soil nutrition (total organic carbon (OC), total nitrogen (TN), available potassium (AK) and the ratio of humic acid to fulvic acid (Ha/Fa)), but were significantly suppressed by iron and aluminum oxide.

Silicon dioxide nanoparticles (SiO₂ NPs) have been shown to alleviate cadmium (Cd) toxicity in plants, but the mechanisms regarding SiO₂ NPs-mediated Cd uptake and detoxification on hyperaccumulators are unknown. In this study, physiological and transcriptomic analyses were performed to investigate the impact of SiO₂ NPs on the growth and Cd accumulation of the Cd-hyperaccumulator Sedum alfredii. The results showed that SiO₂ NPs significantly increased root fresh weight (32.71% to 121.50%) and shoot fresh weight (22.72% to 86.36%). Simultaneously, SiO₂ NPs enhanced the Cd uptake and accumulation by S. alfredii (with maximum increases of 232.14%). In the leaves, the Cd content in the phloem of the Si treatment group increased by 1.24 to 1.79-fold, indicating that SiO₂ NPs enhanced the transport of Cd to the shoots. Furthermore, SiO₂ NPs improved the photosynthetic parameters, with the net photosynthetic rate, transpiration rate and stomatal conductance increasing by 2.86-fold, 1.14-fold, and 1.84-fold of the control, respectively. Furthermore, SiO₂ NPs significantly strengthened the antioxidative enzymes activities (SOD, CAT, POD). Transcriptomic analysis revealed that SiO₂ NPs enhanced the Cd tolerance and accumulation capacity of S. alfredii by upregulating the expression of genes encoding photosynthesis-related functions (PSI, PSII), antioxidant enzymes, cell wall synthesis functions, heavy metal-responsive transcription factors (WRKY, NAC, bZIP, MYB), and Cd chelation and transport protein functions. Combining physiological and transcriptomic analyses, our findings provide the mechanisms of SiO₂ NPs in promoting Cd accumulation and enhancing Cd tolerance in S. alfredii, highlighted the potential of SiO₂ NPs to enhance phytoremediation efficiency.