With the onset of the German occupation of Czechoslovakia, he was forced to return to the Protectorate of Bohemia and Moravia from where he first started as a teacher, in Hlinsko and later in Prague.
[2] Floristic investigations were undertaken in the Jizera Mountains, Belianske Tatras, and Vysoké Tatry, among other locations in the former Czechoslovakia.
[5][6][7] He collected an abundant number of specimens for his herbarium, which is now stored in the Slovak National Museum in Bratislava.
[3] He published 29 important works, the most famous of which is the 1956 collaboration of the author trio Černohorský, Nádvorník, and Servít titled Klíčk určování lišejníků ČSR (Key to identification of lichens of Czechoslovakia).
His name is honoured in several eponymous lichen species: Bryoria nadvornikiana (Gyeln.)