Abstract
Metal nanoparticles (NPs) are finding ever-wider applications in plant production (agricultural and forestry-related) as fertilisers, pesticides and growth stimulators. This makes it essential to examine their impact on a variety of plants, including trees. In the study detailed here, we investigated the effects of nanoparticles of silver and copper (i.e., AgNPs and CuNPs) on growth, and chlorophyll fluorescence, in the seedlings of Scots pine and pedunculate oak. We also compared the ultrastructure of needles, leaves, shoots and roots of treated and untreated plants, under transmission electron microscopy. Seedlings were grown in containers in a peat substrate, prior to the foliar application of NPs four times in the course of the growing season, at the four concentrations of 0, 5, 25 and 50 ppm. We were able to detect species-specific activity of the two types of NP. Among seedling pines, the impact of both types of NP at the concentrations supplied limited growth slightly. In contrast, no such effect was observed for the oaks grown in the trial. Equally, it was not possible to find ultrastructural changes in stems and roots associated with the applications of NPs. Cell organelles apparently sensitive to the action of both NPs (albeit only at the highest applied concentration of 50 ppm) were chloroplasts. The CuNP-treated oaks contained large plastoglobules, whereas those dosed with AgNP contained large starch granules. The NP-treated pines likewise exhibited large numbers of plastoglobules, while the chloroplasts of NP-treated plants in general presented shapes that changed from lenticular to round. In addition, large osmophilic globules were present in the cytoplasm. Reference to maximum quantum yields from photosystem II (Fv/Fm)—on the basis of chlorophyll a fluorescence measurements—revealed a slight debilitation of oak seedlings following the application of both kinds of NP at higher concentrations. In contrast, in pines, this variable revealed no influence of AgNPs, as well as a favourable effect due to the CuNPs applied at a concentration of 5 ppm. Our research also showed that any toxic impact on pine or oak seedlings due to the NPs was limited and only present with higher concentrations.
Highlights
Nanoparticles (NPs) are defined as particles with at least one dimension of less than 100 nm.They have existed in the environment naturally since the beginning of Earth’s history, in ash from volcanoes and forest fires; as sea salt aerosols; and as oxides of iron or other metals in soils, rivers and oceans [1]
Pine seedlings exposed to the 50 ppm dosage of AgNPs had impaired growth in comparison with the control seedlings, in the sense that stems were shorter and the root dry mass was lower
The application of CuNPs had an apparent impact on growth in pines, with the comparisons with the control revealing a smaller root collar diameter, a shorter length of shoots, and a lower dry mass of roots
Summary
Nanoparticles (NPs) are defined as particles with at least one dimension of less than 100 nm. They have existed in the environment naturally since the beginning of Earth’s history, in ash from volcanoes and forest fires; as sea salt aerosols; and as oxides of iron or other metals in soils, rivers and oceans [1]. A second group of “incidental NPs” are produced unintentionally by human activity and are defined as waste or anthropogenic particles. They appear through desertification, biomass burning and coal combustion, as well as in engine exhaust fumes and thanks to mining and other similar activities [2]. More than 1000 products containing nanomaterials are available commercially [1]
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