Abstract: A sand culture experiment was conducted to study the effects of dissolved organic matter (DOM) with different molecular weights and concentrations on the growth and Cu absorption of Chinese cabbage. The DOM extracted from pig manure was fractionated into three molecular weight components as F₁(<1 kDa), F₂(1-14 kDa) and F₃(>14 kDa) by means of equilibrium dialysis. Results suggest that, compared to the control (ultra-pure water), DOM application treatments increased the total root length and the number of root tips of Chinese cabbage by 19%-40% and 45%-91%, respectively, but no significant change was observed for the yield. Furthermore, DOM enhanced the absorption of Cu by Chinese cabbage roots, and Cu concentrations in roots increased with the application amount of DOM in the same molecular weight component. Compared to the control, treatment with 20 mg·L^-1 of F₁, F₂ and F₃ mixed with 2.5 mg·L^-1 of CuSO₄(F₁₃, F₂₃ and F₃₃) increased Cu concentrations in roots by 41%, 37% and 53% (P<0.05), respectively. Moreover, the treatment of F₁₃, F₂₃ and F₂₂(10 mg·L^-1 of F₂ mixed with 2.5 mg·L^-1 of CuSO₄) significantly promoted Cu upward translocation from roots, with the increments in translocation factors of 36%, 48% and 46%, respectively, compared with the control. However, F₃₃ decreased that translocation factor by 26%. Therefore, the molecular weight and addition amount of DOM can both impact Cu uptake and translocation of Cu in Chinese cabbages, low molecular weight of DOM with high concentration will enhance the accumulation and translocation of Cu.

Key words: pig manure, soluble organic component, copper, dialysis, Chinese cabbage