Plastic contamination of ecosystems has increased dramatically over the last decades, raising concerns about the negative impacts of plastic particles on aquatic and terrestrial systems. In recent years, the focus of most research has shifted from large fragments (macroplastic) to micro- (<5 mm) and more recently to nano-plastic (<1000 nm) particles as more evidence has come to light about their ubiquity in water, soils, and living systems, and their effects on ecosystem and human health. In this study, we investigate nanoplastic uptake in the roots of seedlings (1-2 years old) of three different tree species and assess their transport to different tissues. Parts of the main roots of silver birch (Betula pendula Roth), sessile oak (Quercus petraea Matt. [Liebl.]), and Norway spruce (Picea abies [L.] Karst.) were immersed for one or four days in a suspension containing ¹³C-labelled nano-sized polystyrene particles (¹³C-nPS; 99% ¹³C, d = 28 ± 8 (1 σ) nm). Carbon stable isotope analysis showed significant ¹³C enrichment (P < 0.05) in the immersed part of the root after one day of treatment in all three species, and after four days in Q. petraea alone. Signals of significant ¹³C enrichment were also found in the aboveground tissues of the trees. The stem of B. pendula in particular showed a significant ¹³C enrichment after one day of treatment (P < 0.01). This indicates that nanoplastic particles can be taken up through tree roots into the tree’s central cylinder, where they are subsequently conveyed through the tree by acropetal transport via the xylem.