Abstract
Abstract Agriculture is responsible for supplying food, feed, fibres, and an increasing fraction of fuel and raw chemicals for industry. Fulfilling such demands sustainably is one of the major challenges of our time. In this metadata analysis, we offer a quantitative overview of how scientists have been addressing the effects of nanomaterials on plants between 2009 and 2022. The analysis showed that cultivated crops (55%) and plant nutrients (52%) are mostly employed in the studies, pointing to the relevance of these aspects to agriculture. Nevertheless, it also revealed that the concentration of elements as nanomaterials is, generally, more than 2-fold higher than the elemental concentration applied as traditionally formulated fertilisers or those naturally found in soil. Furthermore, the median time span of most studies, i.e. , 49 days for plants cultivated in soil, is still quite short compared to annual crop life cycles (90-120 days), and little attention (19% of treatments) has been devoted to soil microorganisms. Also, only a small fraction of experiments (6%) has been carried out under field conditions. Therefore, the data did not allow establishing correlations between effects and experimental parameters, such as concentration range, soil pH, or time of exposure. These observations point to the intricate relationship between our ability to infer conclusions and the experimental design employed. Finally, this comprehensive and up-to-date overview of the effects of nanomaterials in plant systems raises the question of whether nanomaterials will lead to incremental yield gains by replacing current inputs with nanotechnology-based ones, such as the controlled release of fertilizers and pesticides, or it will disrupt agriculture by attacking problems so far not practically addressed, such as hacking plant stress and defence mechanisms or modulating metabolism and photosystems.
Highlights
How could nanotechnology contribute to the development of more sustainable and productive agriculture? In principle, many inherent properties of nanosized particles (NPs), e.g., larger contact surface, size and shape-dependent solubility, and surface charge flexibility[10,11] might play crucial roles in plant nutrition, disease management, and crop production driving better protection against biotic and abiotic stresses[12], enhancement of photosynthetic efficiency[13,14], control of fertilizer's release[15–17] and even enabling the synthesis of doped-nanodevices for 'smart'-delivery of bioactive compounds and minerals to target tissues[18,19]
This systematic metadata survey aimed at answering ten broad questions: 1) Which nanoparticles (NPs) have been tested?; 2) Which plant species have been exposed to NPs?; 3) What is the size range of NPs?; 4) Did the studies with plants employ any kind of positive control?; 5) Where have the experiments been carried out?; 6) Which plant parts or organs have been exposed to NPs; 7) How long plants have been exposed to NPs?; 8) Which was the concentration range of NPs?; 9) What was the effect of nanomaterials on soil microorganisms?
Coffee plants that received foliar sprays of ca. 68 nm ZnO NPs at 10 mg L1 and, after 40 days of treatment, presented 55% higher photosynthetic activity and 90% higher stomatal conductance compared to ZnSO4 and control treatments[66]
Summary
Manuscript search and selection The present study was carried out by consulting 996 Web of Science indexed research articles related to nanomaterials and plants published between January, 2009 and September, 2020. Bulk particles were considered positive controls when presenting the same composition as the NPs. On the other hand, the soluble control is stated as the effect of the elements ionic form studied on the plants. Experimental environment Four groups of the experimental environment were formed: i) greenhouse, which includes the experiments maintained inside a greenhouse; glasshouse, or screen house with some conditions controlled, such as temperature, photoperiod, watering, and humidity; ii) field, considering experiments that were maintained under field conditions with plants grown in soil without any control of temperature, photoperiod, and humidity; iii) growth chamber, which determines the experiments maintained in a growth chamber, germination chamber, laboratory, or in vitro conditions with some controlled parameters, such as temperature, photoperiod, watering, and humidity; iv) ambient conditions refers to all the experiments performed on environments that did not fit into the previous categories, such as experiments in a recipient (vase, tube, plastic bag) maintained under environmental conditions such as sunlight, weather or ambient atmosphere, indoor or outdoor with room temperature and natural conditions. 892 were employed to build Figure 3c and 99 did not inform, or it was not clear, the experimental environment in which the plants were subjected to the treatments
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