Physiological responses of seashore paspalum and centipedegrass to soil lead contamination stresses

The physiological responses to soil lead contamination stresses at 3 000 mg/kg and 6 000 mg/kg were studied in a pot experiment for two turfgrasses species centipedegrass (Eremochloa ophiuroides) and seashore paspalum (Paspalum vaginatum). The results showed that there were significant differences between two turfgrass species under the two lead stress regimes. Under 3 000 mg/kg Pb2+ stress, the leaf chlorophyll content, Fv/Fm and osmotic potential in centipedegrass did not changed significantly, while the electrolyte leakage (EL) increase significantly at 12 d, and the leaf relative water content (RWC) decrease significantly at 24 d. The visual turf quality maintained above the acceptable level (6.0) throughout the experiment period though a significant decline occurred after 4 d. Under 6 000 mg/kg Pb2+ stress, all physiological indexes in centipedegrass changed significantly at 4 d, and plants died at 12 d. In contrast, under 3 000 mg/kg Pb2+ stress, seashore paspalum did not decreased in leaf Fv/Fm, osmotic potential and chlorophyll content, which were significant higher than the control at 12 d, 16 d, 24 d. There were no significant differences in EL and visual turf quality between 3 000 mg/kg Pb2+ treatment and the control. Although a significant decrease occurred in leaf RWC at 12 d, it recovered at 24 d. Under 6 000 mg/kg Pb2+ stress, chlorophyll content of seashore paspalum still maintained the control level. The EL increased significantly after 4 d, and the osmotic potential, RWC and Fv/Fm decreased significantly after 4 d, but they recovered to the control level at 12 d, 16 d, 20 d, and 20 d, respectively. Although visual turf quality was lower than the control, it still maintained above the acceptable level throughout the experiment period. These results indicated that seashore paspalum had the capacity to repair the Pb2+ injures under the 6 000 mg/kg concentration and lead tolerance was higher than centipedegrass.