Piriformospora indica colonization enhances remediation of cadmium and chromium co-contaminated soils by king grass through plant growth promotion and rhizosphere microecological regulation

Nitrogen removal performance and mechanism in constructed wetlands under saline conditions: Role of Canna indica inoculated with Piriformospora indica

The phytopromotional root endophytic fungus Piriformospora indica was introduced into the wetland plant Canna indica L. to explore its impact on nitrogen (N) removal in constructed wetlands (CWs) to treat normal and saline (0.9 % NaCl) wastewater. P. indica colonization increased total nitrogen, NH4+-N, and NO3--N removal efficiencies under normal and saline conditions, with NO3--N removal rates significantly increasing by 17.5 % under saline conditions (P<0.05). N removal by plant uptake improved by 26.1 % and 27.7 % under normal and saline conditions due to P. indica-mediated growth-promoting effects. Salt-tolerant denitrifiers and nitrifiers guaranteed the dominant role of microbial degradation in N removal under saline conditions. P. indica inoculation considerably improved the contribution of Nocardioides and Nitrosomnas to dissimilatory/assimilatory nitrate reduction and nitrification genes, respectively. These findings elucidate the mechanisms and potential applications of P. indica-mediated phytoremediation in practical wastewater treatment under varying salty conditions.

Serendipita indica Drives Sulfur-Related Microbiota in Enhancing Growth of Hyperaccumulator Sedum alfredii and Facilitating Soil Cadmium Remediation

Endophytic fungus Serendipita indica can bolster plant growth and confer protection against various biotic and abiotic stresses. However, S. indica-reshaped rhizosphere microecology interactions and root-soil interface processes in situ at the submicrometer scale remain poorly understood. We combined amplicon sequencing and high-resolution nano X-ray fluorescence (nano-XRF) imaging of the root-soil interface to reveal cadmium (Cd) rhizosphere processes. S. indica can successfully colonize the roots of Sedum alfredii Hance, which induces a remarkable increase in shoot biomass by 211.32% and Cd accumulation by 235.72%. Nano-XRF images showed that S. indica colonization altered the Cd distribution in the rhizosphere and facilitated the proximity of more Cd and sulfur (S) to enter the roots and transport to the shoot. Furthermore, the rhizosphere-enriched microbiota demonstrated a more stable network structure after the S. indica inoculation. Keystone species were strongly associated with growth promotion and Cd absorption. For example, Comamonadaceae are closely related to the organic acid cycle and S bioavailability, which could facilitate Cd and S accumulation in plants. Meanwhile, Sphingomonadaceae could release auxin and boost plant biomass. In summary, we construct a mutualism system for beneficial fungi and hyperaccumulation plants, which facilitates high-efficient remediation of Cd-contaminated soils by restructuring the rhizosphere microbiota.

Mitigating sediment cadmium contamination through combining PGPR Enterobacter ludwigii with the submerged macrophyte Vallisneria natans

Sediment cadmium contamination poses risks to aquatic ecosystems. Phytoremediation is an environmentally sustainable method to mitigate cadmium contamination. Submerged macrophytes are affected by cadmium stress, but plant growth-promoting rhizobacteria (PGPR) can restore the health status of submerged macrophytes. Herein, we aimed to reduce sediment cadmium concentration and reveal the mechanism by which the combined application of the PGPR Enterobacter ludwigii and the submerged macrophyte Vallisneria natans mitigates cadmium contamination. Sediment cadmium concentration decreased by 21.59% after submerged macrophytes were planted with PGPR, probably because the PGPR colonized the rhizosphere and roots of the macrophytes. The PGPR induced a 5.09-fold increase in submerged macrophyte biomass and enhanced plant antioxidant response to cadmium stress, as demonstrated by decreases in oxidative product levels (reactive oxygen species and malondialdehyde), which corresponded to shift in rhizosphere metabolism, notably in antioxidant defence systems (i.e., the peroxidation of linoleic acid into 9-hydroperoxy-10E,12Z-octadecadienoic acid) and in some amino acid metabolism pathways (i.e., arginine and proline). Additionally, PGPR mineralized carbon in the sediment to promote submerged macrophyte growth. Overall, PGPR mitigated sediment cadmium accumulation via a synergistic plantmicrobe mechanism. This work revealed the mechanism by which PGPR and submerged macrophytes control cadmium concentration in contaminated sediment.

The Influence of Piriformospora indica Colonization on the Root Development and Growth of Cerasus humilis Cuttings

Numerous studies have shown that the endophytic fungus Piriformospora indica has a broad range of promoting effects on root development and plant growth in host plants. However, there are currently no reports on the application of this fungus on Cerasus humilis. This study first compared the colonization ability of P. indica on 11 C. humilis varieties and found that the colonization rate of this fungus on these varieties ranged from 90% to 100%, with the colonization rate of the varieties '09-01' and 'Nongda 7' being as high as 100%. Subsequently, the effect of P. indica on root development and plant growth of C. humilis was investigated using cuttings of '09-01' and 'Nongda 7' as materials. P. indica colonization was found to increase the biomass of '09-01' and 'Nongda 7' plants; root activity, POD enzymes, and chlorophyll content were also significantly increased. In addition, indole-3-acetic acid (IAA) content in the roots of C. humilis plants increased after colonization, while jasmonic acid (JA) and 1-aminocyclopropane-1-car- boxylic acid (ACC) content decreased. In conclusion, it has been demonstrated that P. indica can promote the growth of C. humilis plants by accelerating biomass accumulation, promoting rooting, and enhancing the production of photosynthetic pigments, as well as regulating hormone synthesis.

Effects of three plant growth-promoting bacterial symbiosis with ryegrass for remediation of Cd, Pb, and Zn soil in a mining area

The quality of soil containing heavy metals (HMs) around nonferrous metal mining areas is often not favorable for plant growth. Three types of plant growth promoting rhizobacteria (PGPR)-assisted ryegrass were examined here to treat Cd, Pb, and Zn contaminated soil collected from a nonferrous metal smelting facility. The effects of PGPR-assisted plants on soil quality, plant growth, and the migration and transformation of HMs were evaluated. Results showed that inter-root inoculation of PGPR to ryegrass increased soil redox potential, urease, sucrase and acid phosphatase activities, microbial calorimetry, and bioavailable P, Si, and K content. Inoculation with PGPR also increased aboveground parts and root length, P, Si, and K contents, and antioxidant enzyme activities. The most significant effect was that the simultaneous inoculation of all three PGPRs increased the ryegrass extraction (%) of Cd (59.04-79.02), Pb (105.56-157.13), and Zn (27.71-40.79), compared to CK control (without fungi). Correspondingly, the inter-root soil contents (%) of total Cd (39.94-57.52), Pb (37.59-42.17), and Zn (34.05-37.28) were decreased compared to the CK1 control (without fungi and plants), whereas their bioavailability was increased. Results suggest that PGPR can improve soil quality in mining areas, promote plant growth, transform the fraction of HMs in soil, and increase the extraction of Cd, Pb, and Zn by ryegrass. PGPR is a promising microbe-assisted phytoremediation strategy that can promote the re-greening of vegetation in the mining area while remediating HMs pollution.