The highest percentages of living roots in total underground biomass (63.7-68.7%) were recorded in all natural stands and in unfertilized recultivated stands, while in fertilized recultivated stands the share of living root biomass was mostly c50%. In natural grasslands, cutting and the first fertilization resulted in an increase of living root biomass from 1.8 kg.m-2 (in the untreated stand) to 2.11 kg. m-2 (in a stand with application of 100 kg.ha-1 of N), while in the recultivated stands this level of fertilization reduced the dry mass of living roots to 1.18 kg .m-2 in comparison with the unfertilized recultivated stand (1.66 kg.m-2). -Authors