Low molecular weight organic acids in root exudates and cadmium accumulation in cadmium hyperaccumulator Solanum nigrum L. and non-hyperaccumulator Solanum lycopersicum L.

Changes in the roots exudation of low molecular weight organic acids (LMWOA), cadmium (Cd) accumulation and translocation and soil solution pH in Solanum nigrum L., the Cd-hyperaccumulator were examined and compared with a non-hyperaccumulator Solanum lycopersicum L. The differences were significant (P < 0.05 or < 0.01) between S. nigrum and S. lycopersicum for all the five LMWOA at all soil levels. The total amount of LMWOA exuded by S. nigrum was significantly higher than that of S. lycopersicum (P < 0.05 or < 0.01). The S. nigrum accumulated and translocated more Cd than S. lycopersicum. The soil solution pH of S. nigrum was significantly lower than S. lycopersicum. The S. nigrum with higher concentrations of LMWOA in roots exudation accumulated more Cd in the plants. The results indicated tha LMWOA secretion by S. nigrum root, especially in Cd-contaminated soils, was likely to be an important role in Cd hyperaccumulation.