The Rhizosphere Regulation Of Engineered Nanomaterials To Promote Crop Production

The rapid growth of the global population has resulted in enormous challenges to food production.Nano agricultural technology stands as a highly promising technology for the 21st century,with the potential substantially enhance crop production and promote environmentally sustainable agriculture.Nano fertilizers and nano pesticides exhibit a 20-30%higher efficacy in comparison to conventional agricultural products,thus presenting broad prospects for the agriculture sector.The rhizosphere,a narrow area where plant roots,soil,and soil microorganisms interact,serves as a crucial gateway for the transfer of nutrients from the soil to plants.The rhizosphere processes can significantly influence the bioavailability of nutrients and nanomaterials（NMs）before they uptake by plants.However,there is a lack of research regarding the regulation of the geochemical behavior and bioavailability of NMs by rhizosphere processes,limiting our ability to optimize crop production.Herein,this study investigated the physiological response mechanisms of rice and soybean plants to silicon dioxide（Si O₂）and iron based NMs,respectively,aiming at NMs-induced rhizosphere processes,as well as the geochemical behavior and bioavailability of NMs driven by these processes.The concrete results of the study are outlined below:（1）An in situ rhizobox system was established and used to explore the effects of 50 mg L^-1 Si O₂ NMs on rice plants.Compared with the control and Na₂Si O₃ treatments,Si O₂ NMs increased the biosynthesis and transportation of oxalic acid in rice,which was subsequently secreted to the rhizosphere.Besides,Si O₂ NMs significantly increased the content of Si（OH）₄in the rhizosphere.Oxalic acid provided carbon sources and energy for soil microorganisms,optimizing rhizospheric microbial communities,and enhancing nitrogen fixation,resulting in an increase in the total nitrogen content in rice.In addition,the content of plant hormones（IAA,CTK,and GA）and the relative expression of key genes（Os MOC,Os FON,and Os TB）related to rice tillering were regulated by Si O₂ NMs.As a result,rice yield was promoted by 36.0%.（2）The effects of foliar spraying of 10 mg L^-1 iron-based NMs on soybean plants were examined.It was showed that NMs increased the expression of key genes（Gm PAL,Gm C4H,Gm4CL,and Gm CHS）and the activity of key enzymes（PAL）involved in flavonoids biosynthesis.As a result,the content of flavonoids in soybean shoots was improved.These flavonoids were transported to the root,and secreted into the rhizosphere,resulting in a significant increase in flavonoid content in the rhizosphere.Upon entering the rhizosphere,flavonoids acted as signal molecules to recruit rhizobia for colonization,stimulating the development of root nodules and increasing the leghemoglobin content of nodules.This,in turn,strengthened the nitrogen fixation and ultimately increased the nitrogen content by 8.2-46.5%in soybeans,the yield（pod number and grain biomass）and quality（flavonoids,soluble protein,and elemental nutrients）of soybeans were improved at least by 14.0%.Moreover,compared with the conventional iron fertilizer（EDTA-Fe）,the effect of iron-based NMs is remarkable.（3）The effect of 50 mg L^-1 Si O₂ NMs on the resistance of rice plants was studied.It was showed that Si O₂ NMs significantly increased the content of physical barriers such as trichomes,siliceous cells,and lignin in rice leaves,and increased the level of chemical barriers such as total phenols and proline.It was not found in the Na₂Si O₃ treatment.Furthermore,fluorescence labeling experiments revealed that Si O₂ NMs were directly deposited on rice silica cells and trichomes,strengthening the hardness of tissues.Multiple omics techniques were used to show that the increased resistance of rice by Si O₂ NMs was due to the increased synthesis of jasmonic acid and salicylic acid,and the activation of their signal transduction pathways.Biological experiments confirmed that Si O₂ NMs enhanced the resistance of rice to insects（brown planthopper and armyworm）and rice blast.Si O₂ NMs also increased the hundred-grain weight（18.2-35.2%）and gluten content（10.6-78.4%）of rice,indicating an overall improvement in the yield and quality of rice.In summary,the present study offers insights into the regulatory mechanisms of NMs in the rhizosphere and suggests the potential for enhancing crop production and ensuring global food security through maximizing the role of rhizosphere in promoting the application of NMs in agriculture.