Exploring the potential: Can arsenic (As) resistant silicate-solubilizing bacteria manage the dual effects of silicon on As accumulation in rice?

Rice (Oryza sativa L.) cultivation in regions marked by elevated arsenic (As) concentrations poses significant health concerns due to As uptake by the plant and its subsequent entry into the human food chain. With rice serving as a staple crop for a substantial share of the global population, addressing this issue is critical for food security. In flooded paddy soils, where As availability is pronounced, innovative strategies to reduce As uptake and enhance agricultural sustainability are mandatory. Silicon (Si) and Si nanoparticles have emerged as potential candidates to mitigate As accumulation in rice. However, their effects on As uptake exhibit complexity, influenced by initial Si levels in the soil and the amount of Si introduced through fertilization. While low Si additions may inadvertently increase As uptake, higher Si concentrations may alleviate As uptake and toxicity. The interplay among existing Si and As availability, Si supplementation, and soil biogeochemistry collectively shapes the outcome. Adding water-soluble Si fertilizers (e.g., Na2SiO3 and K2SiO3) has demonstrated efficacy in mitigating As toxicity stress in rice. Nonetheless, the expense associated with these fertilizers underscores the necessity for low cost innovative solutions. Silicate-solubilizing bacteria (SSB) resilient to As hold promise by enhancing Si availability by accelerating mineral dissolution within the rhizosphere, thereby regulating the Si biogeochemical cycle in paddy soils. Promoting SSB could make cost-effective Si sources more soluble and, consequently, managing the intricate interplay of Si's dual effects on As accumulation in rice. This review paper offers a comprehensive exploration of Si's nuanced role in modulating As uptake by rice, emphasizing the potential synergy between As-resistant SSB and Si availability enhancement. By shedding light on this interplay, we aspire to shed light on an innovative attempt for reducing As accumulation in rice while advancing agricultural sustainability.

Diazinon degradation by bacterial endophytes in rice plant (Oryzia sativa L.): A possible reason for reducing the efficiency of diazinon in the control of the rice stem-borer.

It is well known that microorganisms can reduce the effectiveness of organophosphate pesticides after their application. But, little information is available concerning the effect of rice endophytic bacteria on the degradation of diazinon, an organophosphate pesticide used in control of the rice stem-borer, absorbed by the rice plant. Thus, aim of this study was to characterize the endophytic bacterial isolates, isolated from diazinon-treated and non-treated rice plants in paddy fields, in terms of diazinon degradation and to investigate whether potent isolates that degrade diazinon in vitro might have the same effect in the rice plant. The results showed that all endophytic isolates, isolated from both groups of rice plants (diazinon-treated and non-treated rice plants), could grow in mineral salt medium (MSM) supplemented with diazinon (20 mg L-1) as a sole carbon source, and 3.79-58.52% of the initial dose of the insecticide was degraded by the isolates within 14 d of incubation. Phylogenetic analysis based on 16 S rRNA sequencing indicated that the potent isolates (DB26-R and B6-L) clearly belonged to the Bacillus genus. The diazinon concentrations in rice plants co-inoculated with B. altitudinis DB26-R and B. subtilis subsp. Inaquosorum B6-L and single-inoculated with these strains were reduced significantly compared with endophyte-free rice plants. These results provide unequivocal evidence that the rice endophytic bacteria, in addition to in vitro degradation of diazinon, are also involved in the rapid inactivation of diazinon in rice plants treated with diazinon (in vivo degradation of diazinon).

Phosphate-solubilizing bacteria and silicon synergistically augment phosphorus (P) uptake by wheat (Triticum aestivum L.) plant fertilized with soluble or insoluble P source.

Phosphorus (P) deficiency is one of the major problems in agricultural soils for crop production around the world. Use of silicon (Si) and phosphate-solubilizing bacteria (PSB) is known as one of the most effective and economical ways for increasing P availability and improving P use efficiency under low P conditions. However, little is known about the alleviative role of Si and PSB together in mitigating P-deficiency stress and in improving P use efficiency in Triticum aestivum L. (wheat), as one of the most important crop plants worldwide. Consequently, aim of the research was to study the combined and single effects of Si (0, 150, 300, and 600 mg kg-1 added as silicic acid) and PSB (B0, Bacillus simplex UT1, and Pseudomonas sp. FA1) on P uptake by wheat plant fertilized with soluble or insoluble P (Esfordi rock phosphate, RP) in a completely randomized design with factorial arrangement through a perlite potted experiment. In addition, the effects of various treatments on wheat shoot and root dry weight, activity of catalase, superoxide dismutase, and peroxidase enzymes, and the uptake of Si and potassium (K) by this plant were also investigated. Both shoot and root biomass of wheat plants were markedly reduced when grown in RP-fertilized medium compared with those grown in soluble P-fertilized medium. The PSB strains and Si levels independently improved all the aforementioned parameters. Application of Si to wheat plants grown in soluble P or insoluble P medium markedly enhanced P use efficiency. According to the results of this study, Si not only increased the uptake of P from sparingly soluble-P source (RP), but also enhanced uptake of P from water-soluble P source. Both Pseudomonas sp. FA1 and B. simplex UT1 showed a considerable role in improvement of root and shoot biomass and uptake of P (and K and Si) under both soluble and insoluble P fertilization conditions with Pseudomonas sp. FA1 being more effective than B. simplex UT1. However, the combined application of the PSB with Si resulted in the greatest enhancement in wheat plant P uptake and other measured parameters. Addition of 600 mg Si kg-1 and Pseudomonas sp. FA1 significantly increased the P shoot concentration of wheat plant fertilized with RP to an adequate level (>0.3%) in the range of P-fertilized plants. Therefore, in addition to PSB application, Si should be considered as soil amendment in agricultural soils deficient in plant available Si as a means of sustainable agriculture with respect to possible savings of scarce P resources (P-fertilizers). The information on the availability of P following PSB and Si addition to plant growth medium may help in better management of P fertilization.