Zinc and Cadmium Tolerance in Different Ecotypes of Elymus Nutans from Alpine Grassland of Qinghai-Tibet Plateau

Abstract

ABSTRACT Qinghai-Tibet Plateau was a clean environment in the past. Zinc (Zn) and cadmium (Cd) present in soils now. We postulated that the dominant native grass Elymus nutans is tolerant to Zn and Cd. We investigated the effects of Cd-Zn interactions on seed germination, seedling growth, physiological stress, and their uptake in plants of E. nutans. Two ecotypes, Population1 (POP1, altitude 2450 m) and Population2 (POP2, 3300 m), were selected from alpine grassland of Qinghai-Tibet Plateau. Germination and growth parameters were measured after Cd as CdSO4 · 8H2O (15–100 mg l−1) and Zn as ZnSO4 · 7H2O (40–300 mg l−1) were applied. Zn and Cd affected the germination and early seedling growth of both ecotypes. Below 50 mg l−1, Zn promoted seed germination and plant growth, while 300 mg l−1 Zn significantly inhibited it. All levels of Cd had an inhibitory effect. Zn and Cd affected the POP2 above-ground dry weight more than POP1 and reduced root growth more than shoot growth. The measurement of metal accumulation showed that Zn application suppressed Cd accumulation in plants under the lower Cd (< 20 mg l−1) treatments, while above 20 mg l−1, Cd had an antagonistic effect on Zn uptake. Cadmium and Zn alone or in combination induced oxidative stress. The results suggest that responses to Cd and Zn and their interactions vary with concentration: moderate levels of heavy metals activated the species’ protective system, but higher concentrations destroyed it. We concluded that this species has differing abilities to tolerate Zn and Cd related to their original habitats.