**Acknowledgements**

We thank prof. J. D. Brooker for critical reading and language corrections of the manuscript. We are grateful to Dr. Jens Hartmann, Donau University, Krems, Austria, for the electron-microscopy photograph.

This work was supported by the National Program of Sustainability I, ID: LO1416 and by the Program Interreg V-A Austria-Czech Republic, project ATCZ172 REEgain.
