Mechanisms of Arbuscular Mycorrhizal Fungi Increasing Silicon Uptake by Rice.

Arbuscular mycorrhizal fungi (AMF) influence silicon (Si) uptake by plants, but the mechanisms remain unclear. This study investigated the mechanisms of AMF-mediated Si uptake by rice, a model Si-accumulating plant, and explored the tripartite interactions among AMF, Si, and phosphorus (P). AMF inoculation increased shoot Si content by 97% when supplied with silicic acid and by 29% with calcium silicate and upregulated expression of Si transporters Lsi1 and Lsi2 in roots. Supplying Si only to AMF hyphae increased the root Si content by 113%, indicating direct Si uptake by hyphae. Mechanisms of AMF-induced Si uptake were elucidated: 1) direct Si uptake by hyphae, 2) increased silicate dissolution, and 3) upregulation of Si transporters. Silicon application also increased AMF colonization by 28%, and the absence of interactions was observed on P uptake. Altogether, AMF support Si acquisition and Si fosters AMF colonization in rice, whereas the P uptake depends more on AMF than on Si.

The adsorption-diffusion model and biomimetic simulation reveal the switchable roles of silicon in regulating toxic metal uptake in rice roots.

Soil contamination by heavy metals has become a serious threat to global food security. The application of silicon (Si)-based materials is a simple and economical method for producing safe crops in contaminated soil. However, the impact of silicon on the heavy-metal concentration in plant roots, which are the first line in the chain of heavy-metal entering plants and causing stress and the main site of heavy-metal deposition in plants, remains puzzling. We proposed a process-based model (adsorption-diffusion model) to explain the results of a collection of 28 experiments on alleviating toxic metal stress in plants by Si. Then we evaluated the applicability of the model in Si-mitigated trivalent chromium (Cr[III]) stress in rice, taking into account variations in experimental conditions such as Cr(III) concentration, stress duration, and Si concentration. It was found that the adsorption-diffusion model fitted the experimental data well (R2 > 0.9). We also verified the binding interaction between Si and Cr in the cell wall using SEM-EDS and XPS. In addition, we designed a simplified biomimetic device that simulated the Si in cell wall to analyze the dual-action switch of Si from increasing Cr(III) adsorption to blocking Cr(III) diffusion. We found that the adsorption of Cr(III) by Si decreased from 58% to 7% as the total amount of Cr(III) increased, and finally the diffusion blocking effect of Si dominated. This study deepens our understanding of the role of Si in mitigating toxic metal stress in plants and is instructive for the research and use of Si-based materials to improve food security.

Soil Microbial Co-Occurrence Patterns under Controlled-Release Urea and Fulvic Acid Applications.

The increasing amount of agricultural applications of controlled-release urea (CRU) and fulvic acids (FA) demands a better understanding of FA's effects on microbially mediated nitrogen (N) nutrient cycling. Herein, a 0-60 day laboratory experiment and a consecutive pot experiment (2016-2018) were carried out to reveal the effects of using CRU on soil microbial N-cycling processes and soil fertility, with and without the application of FA. Compared to the CRU treatment, the CRU+FA treatment boosted wheat yield by 22.1%. To reveal the mechanism of CRU+FA affecting the soil fertility, soil nutrient supply and microbial community were assessed and contrasted in this research. From 0-60 days, compared with the CRU treatment, leaching NO3--N content of CRU+FA was dramatically decreased by 12.7-84.2% in the 20 cm depth of soil column. Different fertilizers and the day of fertilization both have an impact on the soil microbiota. The most dominant bacterial phyla Actinobacteria and Proteobacteria were increased with CRU+FA treatment during 0-60 days. Network analysis revealed that microbial co-occurrence grew more intensive during the CRU+FA treatment, and the environmental change enhanced the microbial community. The CRU+FA treatment, in particular, significantly decreased the relative abundance of Sphingomonas, Lysobacter and Nitrospira associated with nitrification reactions, Nocardioides and Gaiella related to denitrification reactions. Meanwhile, the CRU+FA treatment grew the relative abundance of Ensifer, Blastococcus, and Pseudolabrys that function in N fixation, and then could reduce NH4+-N and NO3--N leaching and improve the soil nutrient supply. In conclusion, the synergistic effects of slow nutrition release of CRU and growth promoting of FA could improve the soil microbial community of N cycle, reduce the loss of nutrients, and increase the wheat yield.

Common and distinct global functional connectivity density alterations in patients with bipolar disorder with and without auditory verbal hallucination during major depressive episodes.

Although an increasing number of studies has explored the neural mechanisms of auditory verbal hallucination (AVH) using many modalities, including neuroimaging, neurotransmitters, and electroencephalography, the etiology of AVH remains unclear. In this study, we investigated the neuroimaging characteristics of AVH in patients with bipolar disorder (BD) experiencing depressive episodes with and without AVH. For this study, we recruited 80 patients with BD and depressive status (40 with and 40 without AVH), and 40 healthy individuals. Their global functional connectivity density (gFCD) was screened by functional magnetic resonance imaging. Differences in gFCD among the three groups were tested using voxel-wise one-way analysis of covariance. Patients in both BD groups demonstrated increased gFCD in the central parietal lobe, insular lobe, and middle cingulate cortex, and decreased gFCD in the posterior parietal cortex, lateral prefrontal cortex, and occipital lobe (all bilateral). We defined these alterations as the common aberrant gFCD pattern for BD with and without AVH. Compared with the other two groups, patients in the BD with AVH group demonstrated increased gFCD in the Broca and Wernicke regions, and decreased gFCD in the hippocampus (all bilateral). We defined these alterations as the distinct aberrant gFCD pattern for BD with AVH. To our knowledge, this report is the first to date to describe gFCD alterations in patients with BD with and without AVH. Our findings suggest that disturbances in brain activity and information communication capacity in patients with BD and AVH are located mainly in the left frontoparietal network, control network, and memory circuit. However, these observations were made only in patients with BD during depressive episodes, and without consideration of many factors, such as the treatment mode, symptom relapse, and BD subtype. Hence, the conclusions of this study merely provide clues for further study, and do not fully represent brain alterations in patients with BD and AVH. Further large-sample cohort studies are needed to clarify and expand on these findings.