Nanotechnology in Plant Growth Promotion and Protection. Группа авторов

dry biomassIncrease in phosphorus contentChanges in soil organic matter Zahra et al. (2019) 30 Pisum sativum, Grown for 28 days in contaminated soil n.a. n.a. 80, 800 mg/kg Reduction in the availability of important soil mineral nutrients (Mn, Fe, P)Reduction in root lengthIncrease in shoot length Bellani et al. (2020)

      Application of TiO₂NPs on seeds may help with germination through better water uptake and oxygen absorption (Zheng et al. 2005; Feizi et al. 2013a,b) and plant protection due to antimicrobial and antifungal effects of TiO₂NPs (Navarro et al. 2008). This may be a good approach for plants having seed germination problems such as medical herbs (Feizi et al. 2013b).

      Throughout the various growth stages of plants, both foliar and soil applications of TiO₂NPs were shown to improve the plant growth, through improvements in root and shoot elongation, root and shoot biomass, increased number of root nodules, increased yield of seeds, fruits, or other plant parts involved in food production. Besides, other improvements in plant health, like an increase in chlorophyll production, production of soluble leaf protein, and several amino acids were also recorded. At right concentrations, an increase in essential macronutrients (N, P, K, Na, and Ca), and micronutrients (Fe, Mn, and Zn) was observed (Kužel et al. 2003; Yang et al. 2006; Raliya et al. 2015a,b; Tan et al. 2017). This may be beneficial for agriculture and the environment, since it decreases the requirement of fertilizers. Plants were also shown to have increased resistance to draught after the application of TiO₂NPs. A foliar spray may also help in the reduction in uptake of toxic elements such as Cd (Lian et al. 2020). Another avenue of TiO₂NPs application is its potential pesticidal properties. TiO₂NPs were used to protect plants against cotton leafworms (Shaker et al. 2017), Cercospora leaf spot, brown blotch, Curvularia leaf spot, and bacterial leaf blight (Owolade and Ogunleti 2008).

      Although TiO₂NPs can be used alone to inhibit crop pests, its composite formulae can be promisingly utilized to protect plants against various crop diseases. These nanopesticides utilize nanoparticles in several ways. The nanoparticles are used as carriers that help with distribution, dispersity, and wettability of plant surface and they increase pesticide's adhesion (Rajwade et al. 2020). The improved effect of pesticides by nanoformulations with TiO₂ is not the only benefit these composites provide. Degradability in the soil of these nano‐pesticides is also an important aspect and photocatalytic properties of TiO₂NPs were utilized to increase the decomposition of these pesticides in soil (Yan et al. 2005; Guan et al. 2010; Mohamed and Khairou 2011).

2.6 Conclusion and Future Perspective

The application of TiO₂NPs for crop enhancement is a relatively new phenomenon. The available reports clearly indicated that TiO₂NPs influence and enhance plant growth. Most of the studies were done on germination or influence on young plants. The longer duration experiments with plants are still uncommon and the shortage of life cycle studies and multi‐generation studies leaves many unanswered questions. Other avenue that needs more research is the influence of soil types on the interaction between TiO₂NPs and plants. Interaction between soils and nanoparticles is complex and can differ for particles of different sizes and coating. Measuring quantitative and qualitative uptake by plants can also provide more insight. Four areas of research need more focus in the following years.

      1 Long term exposures at low doses: Models of fluxes in environmental compartments predict concentrations of ≤0.001–1000 mg/kg for bio‐solids including soils, with lower concentrations being much more common. Most of the studies were short term, with high concentrations used. Thus, there is a lack of knowledge of the actual environmental conditions in which the nanoparticles influence plant growth.

      2 Nutritional quality and balance of essential elements in plants: TiO2NPs have been shown to affect the uptake of several essential elements including N, P, Ca, Na, Fe, Mn, and Zn. Therefore, it is important to study if nanoparticle use can cause imbalances in plant nutrition and to find what concentrations and which application times have the best effect on the promotion of uptake of the essential nutrient with the least negative effects on plants.

      3 Intergenerational studies and uptake to edible parts: The influence of TiO2NPs or nanoparticles in general is understudied and little is known about the effects across multiple generations. The impact on seed integrity and growth of succeeding generations has been largely uninvestigated. There is also little knowledge about the concentrations of TiO2NPs in edible parts of the plants that can potentially compromise food safety.

      4 Time and method of application: Although there is some evidence for differences between foliar and soil application, more research needs to be undertaken to increase the effect of the application of TiO2NPs on plants and decrease the contamination of soil by them. More comparative studies will provide greater insight and can limit the possible negative effects that the nanoparticles can have on the crops.

      The body of knowledge that covers nanoparticle influence on plants is in the early stages and is largely incomplete. Some of the studies are relatively contradictory, but most of the evidence points toward low toxicity of TiO₂NPs and great potential to enhance crop production at the right application time and concentration ranges. Great effort will be needed to complete the knowledge gaps and balance the potential between increased crop production and the safety of food and the environment.

Acknowledgement

      This work was financial supported by the Slovak Academy of Sciences via grants VEGA 1/0164/17, VEGA 1/0146/18, and KEGA 013SPU‐4/2019; by the Ministry of Education, Youth and Sports of the Czech Republic in the following projects: Project No. SP2019/75, SP2019/50, OP RDE grant number CZ.02.1.01/0.0/0.0/16_019/0000753 “Research center for low carbon energy technologies,” by Masaryk University: project MUNI/A/1294/2019, and by the Materials Research Centre at FCH BUT – Sustainability and Development, REG LO1211, with financial support from National Programme for Sustainability I (Ministry of Education, Youth and Sports of the Czech Republic).

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