EFFECTS OF SOIL ACIDITY AND ACCOMPANYING ION STRESSES ON STRUCTURE OFNODAL ROOTS OF THE TOLERANT SPECIES NARDUS-STRICTA L AND DESCHAMPSIA-FLEXUOSA L

As a result of exploitation of quartizite stone, specific stress condi tions have developed in a locality in Central Slovakia, with a gradien t of soil pH between 2.7 and 5.2. Adult plants of tolerant Nardus stri cta L. and even more tolerant Deschampsia flexuosa L. from this locali ty, growing in the acid soil with pH 3.4 (stressed plants) and unpollu ted soil with pH 5.2 (control plants) were used for the study of quant itative anatomy of their nodal roots. Elemental composition of the soi ls taken from the rhizosphere of the investigated plants was analysed. Cross section area of the whole root, stele, and xylen elements were investigated and evaluated quantitatively, in hand sections taken from the basal parts of the nodal roots. Concentrations of heavy metals Fe , Cu, Zn, Pb, and Ni, did not reach toxic levels in the extremely acid soil. The complex stress conditions of the soil were due to low pH, h igh concentrations of Al3+ and SO4(2-), deficiency in Ca and Mg, and a decrease in Ca:Mg ratio. The stress conditions induced a significant decrease in cross section area of the investigated anatomical traits i n both species, except of the cortical tissue of Deschampsia flexuosa. The reduction of root tissue in this species was also lower in compar ison with the roots of Nardus. The lowered proportion of water-conduct ing tissues within the nodal roots could negatively affect root hydrau lic conductivity and cause water deficiency as additional stress in bo th plant species. Both preservation of cortical tissue and higher prop ortion of water-conducting tissues within the nodal roots of Deschamps ia flexuosa might represent better structural adaptation of this speci es to the complex stress conditions.