Abstract
Metal nanoparticles are gaining ever-wider application in agriculture and forestry, as alternatives to chemical agents used as fertilisers, growth stimulators and pesticides, establishing a need for eco-toxicological risk assessment of these agents. We tested the effects of foliar-applied silver nanoparticles (AgNPs) on chlorophyll a fluorescence and on abundance and species composition of ectomycorrhizal (ECM) colonisation. The application of AgNPs at concentrations of 5, 25 and 50 ppm was found to stimulate the formation of mycorrhizae in seedlings of pedunculate oak, with the highest effect at intermediate concentrations (25 ppm). There were non-linear effects on the relative abundance of ECM fungal species. The proportion of dominant T. terrestris was highest in the control group, whereas the shares of ECM formed by the two other species, S. brunnea and P. involutus, were higher in the treatments with intermediate and maximal concentrations of AgNPs, respectively. Maximum quantum yield of photosystem II (Fv/fm) assessed by chlorophyll a fluorescence measurements revealed slight debilitation of oak seedlings irrespective of the application of AgNPs and their concentrations. This result offered an indirect indication that photosynthesis capacity had no influence on the level of mycorrhization. We hypothesise that foliar AgNPs treatments at concentrations below thresholds of acute toxicity and in the absence of significant effects on chlorophyll a fluorescence may still exert significant influence on biotic interactions including mycorrhizal symbioses by impacting plant hormonal balance, particularly ethylene, and regulatory pathways involved in host control of ECM colonisation.
Highlights
Nanoparticles (NPs) are atomic or molecular aggregates with two dimensions between 1 and 100 nm (Klaine et al 2008)
The proportion of P. involutus ECM was highest in the treatment with the highest dose – 50 ppm of AgNPs (6.6%), and lowest in the control treatment (3.1%). 5.3% were recorded in the 5 ppm treatment, 3.4% in the 25% treatment (Fig. 2)
While chlorophyll a fluorescence is not strictly proportional to the intensity of photosynthesis it seems unlikely that increased levels of mycorrhizal colonisation linked to AgNPs treatments were due to increased photosynthesis, which might have increased the amount of sugar reaching the roots and ECM fungi (Högberg et al 2008)
Summary
Nanoparticles (NPs) are atomic or molecular aggregates with two dimensions between 1 and 100 nm (Klaine et al 2008). It. Research to date points to a differentiated influence of nanoparticles on higher plants, in that both positive and negative effects have been noted (Rizwan et al 2017). Research to date points to a differentiated influence of nanoparticles on higher plants, in that both positive and negative effects have been noted (Rizwan et al 2017) Such differences relate i.a. to species of plant, growth conditions (e.g. in soil or different nutrient media), type and concentration of nanoparticles, means of application (foliar or soil) and dose applied (Ruffini Castiglione and Cremoni 2009; Ma et al 2010; Arruda et al 2015; Rizwan et al 2017), This all ensures. The deployment of nanoparticles (as growth stimulators or plant protection agents) in the nursery production of seedling trees for forestry is linked with certain dangers that influences on both host plant and mycorrhizal partner will prove unfavourable
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