Effects of N fertilizer reduction combined with straw biochar application on the yield, Si, and N nutrition of double-cropping rice.

Nitrogen (N) and silicon (Si) are important nutritional elements for rice. However, excessive N fertili-zer application and the ignorance of Si fertilizer are common in practice. Straw biochar is rich in Si, which can be used as a potential Si fertilizer. In this study, we conducted a consecutive 3-year field experiment to explore the effects of N fertilizer reduction combined with straw biochar application on rice yield, Si and N nutrition. There were five treatments: conventional N application (180 kg·hm-2, N100), 20% N reduction (N80), 20% N reduction with 15 t·hm-2 biochar (N80+BC), 40% N reduction (N60), and 40% N reduction with 15 t·hm-2 biochar (N60+BC). The results showed that compared with N100, 20% N reduction did not affect the accumulation of Si and N in rice; 40% N reduction reduced foliar N absorption, but significantly increased foliar Si concentration by 14.0%-18.8%; while combined application of biochar significantly increased foliar Si accumulation, with an increase of Si concentration by 38.0%-63.3% and Si absorption by 32.3%-49.9%, but further reduced foliar N concentration. There was a significant negative correlation between Si and N concentration in mature rice leaves, but no correlation between Si and N absorption. Compared with N100, N reduction or combined application of biochar did not affect soil ammonium N and nitrate N, but increased soil pH. Nitrogen reduction combined application of biochar significantly increased soil organic matter by 28.8%-41.9% and available Si content by 21.1%-26.9%, with a significant positive correlation between them. Compared with N100, 40% N reduction reduced rice yield and grain setting rate, while 20% N reduction and combined application of biochar did not influence rice yield and yield components. In summary, appropriate N reduction and combined with straw biochar can not only reduce N fertilizer input, but also improve soil fertility and Si supply, which is a promising fertilization method in double-cropping rice fields.

Silica nanoparticles activate defense responses by reducing reactive oxygen species under Ralstonia solanacearum infection in tomato plants.

Silica nanoparticles (SNPs) play an important positive role in enhancing stress resistance of plants. However, their absorption and the mechanisms of resistance in plants are not yet fully understood. In this study, we investigated the uptake of SNPs in tomato plants and explored the physiological and molecular mechanisms of SNPs-mediated bacterial wilt resistance. Folia application of SNPs significantly increased silicon content in tomato leaves and roots by 5.4-fold and 1.8-fold compared with healthy control, respectively. Moreover, foliar-applied SNPs mainly accumulated in the shoots of plants. Interestingly, we found that SNPs significantly reduced wilt severity by 20.71%-87.97%. Under pathogen infection conditions, the Hydrogen peroxide (H2O2) levels and Malondialdehyde (MDA) content in SNPs treated leaves significantly decreased by 16.33%-24.84% and 22.15%-38.54%, respectively, compared to non-treated SNPs leaves. The application of SNPs remarkably increased peroxidase (78.56-157.47%), superoxide dismutase (46.02-51.68%), and catalase (1.59-1.64 fold) enzyme activities, as well as upregulated the expression of salicylic acid-related genes (PR-1, PR-5, and PAL) in tomato leaves. Taken together, our findings demonstrate that SNPs function as important nanoparticles to maintain ROS homeostasis in plants by increasing antioxidant enzyme activity in tomato plants and enhancing plant tolerance to bacterial wilt disease by regulating the expression of salicylic acid-related genes. This study expands our understanding of how plants utilize these nanoparticles to deal with pathogen infection.

Role of Silica Nanoparticles in Abiotic and Biotic Stress Tolerance in Plants: A Review.

The demand for agricultural crops continues to escalate with the rapid growth of the population. However, extreme climates, pests and diseases, and environmental pollution pose a huge threat to agricultural food production. Silica nanoparticles (SNPs) are beneficial for plant growth and production and can be used as nanopesticides, nanoherbicides, and nanofertilizers in agriculture. This article provides a review of the absorption and transportation of SNPs in plants, as well as their role and mechanisms in promoting plant growth and enhancing plant resistance against biotic and abiotic stresses. In general, SNPs induce plant resistance against stress factors by strengthening the physical barrier, improving plant photosynthesis, activating defensive enzyme activity, increasing anti-stress compounds, and activating the expression of defense-related genes. The effect of SNPs on plants stress is related to the physical and chemical properties (e.g., particle size and surface charge) of SNPs, soil, and stress type. Future research needs to focus on the "SNPs-plant-soil-microorganism" system by using omics and the in-depth study of the molecular mechanisms of SNPs-mediated plant resistance.

Silicon Enhances Plant Resistance of Rice against Submergence Stress.

Flooding is an important natural disaster limiting rice production. Silicon (Si) has been shown to have an important role in alleviating varied environmental stress. However, very few studies have investigated the effects and mechanisms of Si in alleviating flood stress in rice. In the present study, wild type rice (cv. Oochikara, WT) and Si-defective mutant (lsi1) were chosen to examine the impacts of Si application on plant growth, photosynthesis, cell structure, and antioxidant enzyme activity of rice exposed to submergence stress at tillering stage. Our results showed that Si application improved root morphological traits, and increased Si uptake and plant biomass of WT under submergence stress, but non-significantly influenced lsi1 mutant. Under submergence stress, leaf photosynthesis of WT was significantly inhibited, and Si application had no significant effects on photosynthetic rate, transpiration rate, stomatal conductance, and intercellular carbon dioxide concentration for both of WT and lsi1 mutant, but the photochemical quenching of WT was increased and the integrity of cell structure was improved. In addition, Si application significantly reduced malondialdehyde concentration and increased the activity of peroxidase and catalase in WT leaves under submergence stress. These results suggested that Si could increase rice plant resistance against submergence stress by improving root morphological traits and chloroplast ultrastructure and enhancing antioxidant defense.

Evaluation of Different Types and Amounts of Amendments on Soil Cd Immobilization and its Uptake to Wheat.

Using amendments is a cost-effective method to soil cadmium (Cd) remediation, whereas knowledge about how different amendments and rates affect remediation efficiency remains limited. This study aimed to evaluate the impacts of different types and amounts of amendments on soil Cd immobilization and its uptake by plants. Biochar (BC), zeolite (ZE), humic acid (HA), superphosphate (SP), lime (L), and sodium sulfide (SS) were applied at three rates (low, medium, and high) ranging from 0.5 to 5%. The concentration of CaCl2-extractable Cd was considerably affected by the amendments, except HA, and the high doses achieved better immobilization effects than the low doses did. The addition of amendments decreased weak acid soluble Cd by 4.1-44.0% but slightly increased the fractions of oxidizable and residual Cd. These amendments (except BC and HA dose of 1%) decreased Cd accumulation in grains by 1.3-68.8% and (except SP) in roots by 16.3-65.5% compared with the control. The SP efficiently immobilized Cd but posed a potential soil acidification risk. Moreover, SS treatment increased the soil electrical conductivity (EC) value and restricted the growth of wheat, possibly due to high-salt stress. BC, ZE, and L exerted significant effects on the reduction in available Cd as the application rate increased. These amendments enhanced Cd immobilization mainly by changing Cd availability in soil and influencing its redistribution in different fractions in soil and root uptake by plants. This study concluded that BC-5%, ZE-1%, and L-0.5% can be used for Cd immobilization in acidic or neutral soils.