Effects of Protaetia brevitarsis frass on rhizosphere properties and chromium-arsenic accumulation in Scutellaria baicalensis grown in contaminated soil.

Dose-Dependent Growth Promotion and Rhizosphere Microbial Community Responses of Silage Maize to Bacillus amyloliquefaciens Biofertilizer

To verify the growth-promoting effects of Bacillus amyloliquefaciens on silage maize (Zea mays L.), optimize its application dosage, and elucidate rhizosphere microecological responses, this study executed field experiments in both conventional and saline-alkali soils. We comprehensively assessed how varying biofertilizer dosages (0, 300, and 600 kg ha−1) influenced crop phenotypes, soil physical and chemical attributes, and rhizosphere microbial communities. Results demonstrated that applying B. amyloliquefaciens substantially enhanced biomass and crude protein accumulation in silage maize, without compromising its ideal carbohydrate profile and fermentation characteristics. The observed growth stimulation was likely linked to efficient mobilization of native soil nutrients. Following biofertilizer application, significant surges in available potassium, available phosphorus, and inorganic nitrogen were recorded at both locations, coupled with successful pH buffering in the saline-alkali plots. Microbial analysis indicated a notable expansion of the copiotrophic Proteobacteria phylum, with the bio-inoculant displaying dose-dependent shifts. Specifically, Xanthobacteraceae was heavily recruited in standard agricultural soils to hasten nutrient mineralization, while stress-tolerant bacterial groups like Nitrosomonadaceae were stimulated under saline-alkali conditions. Furthermore, comprehensive phenotypic and nutritional evaluations demonstrated that, among the tested doses, an application rate of 300 kg ha−1 effectively optimizes crop performance. Higher doses do not yield proportional biological benefits, likely due to the carrying capacity limits of the rhizosphere microecology. In summary, B. amyloliquefaciens can support high-yield and high-quality silage maize production by activating soil nutrients and remodeling the core rhizosphere microbiome in a habitat-specific manner. Among the tested doses, 300 kg ha−1 showed the best performance, but further studies with lower doses and longer durations are needed to determine the true optimal application rate and to assess its economic and environmental sustainability.

Sewage sludge composted and bio-promoters enhance soil nutrient availability and initial development of Astronium fraxinifolium Schott

This study evaluated the effects of sewage sludge composted (SSC, mixed with sugarcane bagasse at 1:1 ratio) and microbial biopromoters on soil fertility and early growth of Astronium fraxinifolium, a native tree with high recovery potential in the Brazilian Cerrado. In a randomized block design (2 × 4 factorial), treatments consisted of two SSC levels (with and without 23 g pot⁻¹ of chemically characterized, environmentally safe compost) and four inoculation treatments (control; Bacillus subtilis - BS; Rhizophagus clarus - RhC; and BS + RhC) with five replicates in 6-L pots. After 150 days, growth, root morphology, gas exchange, and soil properties were evaluated. SSC improved soil fertility (reduced aluminum, increased P, sum of bases, base saturation, and essential micronutrients Fe, Mn, Zn) without inducing heavy metal toxicity, increasing plant height. The SSC + RhC interaction significantly promoted shoot and root biomass, stem diameter, and root surface area/volume. Seedling Quality Index (SQI) was highest under SSC + RhC and SSC + BS. Furthermore, SSC and inoculants significantly enhanced gas exchange parameters, translating into substantially higher photosynthetic performance. Overall, combining this specific SSC rate with biopromoters, particularly Rh. clarus, effectively improved soil chemical properties and seedling vigor. While limited to nursery conditions, these findings demonstrate that this approach successfully promotes high-quality seedlings, establishing a promising baseline for future long-term field validation and dose-response trials in degraded lands.

Enhancing copper and arsenic phytoextraction from calcareous soil through the synergistic interaction of ethylenediaminetetraacetic acid application timing and metal-resistant plant growth-promoting rhizobacteria inoculation.

Remediating calcareous soils co-contaminated with copper and arsenic remains a major challenge due to low metal bioavailability and the risk of chelator-induced phytotoxicity, which can severely limit phytoremediation success. This study investigated a synergistic strategy combining heavy metal-resistant plant growth-promoting rhizobacteria (PGPR) with precisely timed ethylenediaminetetraacetic acid (EDTA) application to improve phytoextraction efficiency in corn (Zea mays). Eight PGPR isolates were obtained from contaminated soil, and three strains (Stenotrophomonas sp. A22, Pseudomonas sp. A2 and A5) were selected based on their high resistance to Cu (up to 400 mg L-1) and As (up to 250 mg L-1), as well as multiple plant growth-promoting traits. In a controlled pot experiment, we evaluated bacterial inoculation and EDTA application at 20, 35, or 45 days after planting on plant growth, physiological performance, and metal uptake. Early EDTA addition (day 20) caused severe phytotoxicity, markedly reducing root and shoot biomass and depressing photosynthetic efficiency (Fv/Fm). In contrast, delaying EDTA application to days 35 or 45 substantially alleviated these adverse effects. PGPR inoculation, particularly with strain A5, further mitigated EDTA-induced stress and improved biomass production and physiological status. The combined PGPR-EDTA treatments significantly increased soil metal bioavailability and enhanced plant uptake, with maximum shoot Cu (214 mg kg-1) and As (99 mg kg-1) concentrations observed with strains A5 or A2 and EDTA application at day 20. Sequential extraction confirmed that these PGPR-EDTA treatments shifted metals from residual and oxide-bound pools into more soluble and exchangeable/carbonate-bound fractions. The findings support a mechanistically informed, optimized phytoremediation strategy for calcareous soils, based on the optimal timing of EDTA application and inoculation with metal-resistant PGPR.

Rhizosphere and growth responses of Eleocharis mutata in soils affected by fresh and weathered crude oil contamination: hormesis effects, rhizobacterial stimulation and phytoremediation potential

Synergistic Effects of Organo-Mineral Fertilization and Phosphorus-Solubilizing Bacteria on Soil Biological Activity and Eggplant Growth in Calcareous Soil

This study was conducted to investigate the effects of a commercial microbial fertilizer containing Bacillus megaterium, Pantoea agglomerans and Pseudomonas fluorescens on soil biological properties and plant growth during eggplant (Solanum melongena L.) cultivation under greenhouse conditions in calcareous soils. While 70% of the phosphorus (P) requirement was supplied via fertigation, the remaining 30% was provided through organo-mineral basal fertilization at four reduction levels (0%, 25%, 50%, 100%) combined with microbial inoculation. Soil samples collected prior to the experiment and at 4 different growth stages were analyzed for physical, chemical, and biological properties, while plant samples collected at the end of the harvest were evaluated for pomological and physiological traits. The results indicated that microbial treatments substantially enhanced soil biological activity. Specifically, the full-dose P + microbial treatment (100+) produced the highest urease, alkaline phosphatase, β-glucosidase activities, and total bacterial count. The 100+ treatment also yielded the most pronounced improvements in soil EC, organic matter, total nitrogen, and available P. Plant parameters, including fruit length, peduncle length, dry biomass, soluble solids content, and chlorophyll concentrations, responded positively to P–microbial combinations. The highest leaf phosphorus concentration was obtained from the 100+ treatment, while the maximum total yield was achieved in both the 100 and 100+ treatments. These findings demonstrate that microbial inoculants create a strong synergy with mineral fertilization by enhancing P bioavailability and nutrient use efficiency. Consequently, it was determined that an integrated microbial-chemical fertilization strategy is an effective method for sustainable eggplant production in calcareous soils.

Effects of different crop intercropping on quality and rhizosphere soil microbial community of Erigeron breviscapus

Obstacles for continuous cropping severely restrict the sustainable production of Erigeron breviscapus. To screen suitable intercropping crops and clarify their dual effects on plant growth, medicinal quality, rhizosphere nutrients, soil enzyme activity, and microbial communities, a pot experiment was conducted using 3-year continuously cropped soil, with monoculture as the control (CK) and four intercropping treatments: (A) Brassica juncea L., (B) corn, (C) purple garlic, and (D) broad bean. The results showed distinct crop-specific positive and negative effects of intercropping. On the positive side, intercropping with corn and broad bean significantly increased the total flavonoid content; corn and purple garlic intercropping elevated soil catalase and phosphatase activities, while all four intercropping modes improved soil pH, organic matter, and available nutrients and significantly enriched the richness and diversity of rhizosphere bacterial communities, except in the purple garlic treatment. A correlation analysis indicated that the beneficial phylum Actinobacteriota was positively correlated with soil pH and hydrolase activities, and intercropping effectively reduced the relative abundance of pathogenic Fusarium. However, substantial negative drawbacks were observed across all intercropping systems. All intercropping treatments suppressed aboveground leaf development and root morphological indicators of E. breviscapus, and the scutellarin content was significantly lower than CK at all sampling stages. Intercropping with purple garlic drastically reduced fungal community richness and the number of unique fungal operational taxonomic units, which may weaken soil disease-suppressive capacity. Although corn and broad bean partially alleviated rhizosphere microecological degradation caused by continuous cropping, they simultaneously induced irreversible declines in vegetative growth and key medicinal component accumulation. In conclusion, no fully balanced optimal intercropping combination was identified in this pot experiment; corn and broad bean showed partial potential for soil restoration under controlled pot culture conditions; however, their adverse impacts on medicinal quality and plant growth cannot be ignored. Large-scale field positioning trials are urgently required to verify these pot-derived findings and optimize intercropping configuration, planting density, and cultivation regulation before the coordinated intercropping scheme can be applied to field E. breviscapus production to balance soil health, crop growth, and medicinal efficacy.