Effects of three graphene-based materials on the growth and photosynthesis of Brassica napus L.

The environmental safety and threats of graphene-based materials (GBMs) to the agroecosystem have attracted increasing attention in recent years. However, the mechanisms underlying the effects of GBMs on plants remain unclear. Here, we investigated the phytotoxicity of reduced graphene oxide (RGO), graphene oxide (GO) and amine-functionalized graphene (G-NH2) on Brassica napus L. The results revealed that RGO impaired photosynthesis mainly by decreasing the chlorophyll content and Rubisco activity. A further gene-level analysis suggested that this effect of RGO might be due to its toxicity on sulfate transmembrane transporter and nitrogen metabolism, which ultimately led to nutrient imbalance. However, GO directly damaged the photosystem by disrupting the chloroplast structure, and a decrease in Rubisco activity indicated that GO also inhibits carbon fixation. Further gene-level analysis demonstrated that GO has toxicity on the chloroplast membrane, photosystem, photosynthethic electron transport and F-type ATPase. In addition, G-NH2 at 10-1000 mg L-1 showed no significant toxicity. These findings shed light on the potential mechanism for the toxicity of GBMs on plants for risk assessment.

Potassium humate supplementation improves photosynthesis and agronomic and yield traits of foxtail millet.

Foxtail millet is a highly nutritious crop, which is widely cultivated in arid and semi-arid areas worldwide. Humic acid (HA), as a common plant growth regulator, is used as an organic fertilizer and feed additive in agricultural production. However, the impact of potassium humate KH on the photosynthetic rate and yield of foxtail millet has not yet been studied. We explored the effects of KH application on the morphology, photosynthetic ability, carbon and nitrogen metabolism, and yield of foxtail millet. A field experiment was performed using six concentrations of KH (0, 20, 40, 80, 160, and 320 kg ha-1) supplied foliarly at the booting stage in Zhangza 10 cultivar (a widely grown high-yield variety). The results showed that KH treatment increased growth, chlorophyll content (SPAD), photosynthetic rate (Pn), transpiration rate (Tr), and stomatal conductance (Gs). In addition, soluble protein content, sugar content, and nitrate reductase activity increased in KH-treated plants. With increased KH concentration, the effects became more evident and the peak values of each factor were achieved at 80 kg ha-1. Photosynthetic rate showed significant correlation with SPAD, Tr, Gs, and soluble protein content, but was negatively correlated with intercellular CO2 concentration. Compared to that of the control, the yield of foxtail millet under the T2, T3, T4, and T5 (40, 80, 160, and 320 kg ha-1 of KH) treatments significantly increased by 6.0%, 12.7%, 10.5%, and 8.6%, respectively. Yield exhibited a significant positive correlation with Tr, Pn, and Gs. Overall, KH enhances photosynthetic rate and yield of foxtail millet, therefore it may be conducive to stable millet production. These findings may provide a theoretical basis for the green and efficient production of millet fields.

Nanopesticide Formulation from Pyraclostrobin and Graphene Oxide as a Nanocarrier and Application in Controlling Plant Fungal Pathogens.

Efficient and environment-friendly nanopesticide delivery systems are critical for the sustainable development of agriculture. In this study, a graphene oxide nanocomposite was developed for pesticide delivery and plant protection with pyraclostrobin as the model pesticide. First, graphene oxide-pyraclostrobin nanocomposite was prepared through fast adsorption of pyraclostrobin onto graphene oxide with a maximum loading of 87.04%. The as-prepared graphene oxide-pyraclostrobin nanocomposite exhibited high stability during two years of storage, suggesting its high potential in practical application. The graphene oxide-pyraclostrobin nanocomposite could achieve temperature (25 °C, 30 °C and 35 °C) and pH (5, 7 and 9) slow-release behavior, which overcomes the burst release of conventional pyraclostrobin formulation. Furthermore, graphene oxide-pyraclostrobin nanocomposite exhibited considerable antifungal activities against Fusarium graminearum and Sclerotinia sclerotiorum both in vitro and in vivo. The cotoxicity factor assay revealed that there was a synergistic interaction when graphene oxide and pyraclostrobin were combined at the ratio of 1:1 against the mycelial growth of Fusarium graminearum and Sclerotinia sclerotiorum with co-toxicity coefficient values exceeding 100 in vitro. The control efficacy of graphene oxide-pyraclostrobin nanocomposite was 71.35% and 62.32% against Fusarium graminearum and Sclerotinia sclerotiorum in greenhouse, respectively, which was higher than that of single graphene oxide and pyraclostrobin. In general, the present study provides a candidate nanoformulation for pathogenic fungal control in plants, and may also expand the application of graphene oxide materials in controlling plant fungal pathogens and sustainable agriculture.