Abstract: Heavy metal pollution caused by the unreasonable exploitation of mineral resources becomes serious in China. Phytoremediation is an effective way to dispose heavy metal pollution. This study aimed to screen a remediation plant that can suffer from heavy metal stress from tailings. Moringa oleifera is a widely introduced species in the dry-heat valley of Yunnan. We conducted a pot experiment with different levels of combined Cd-Pb-Zn-Cu stresses to explore the responses of leaf photosynthesis, growth characteristics, and biomass allocation and thus to reveal the adaptation mechanism and the enrichment characteristics of M. oleifera to combined heavy metal stresses. The results showed that combined heavy metal stresses significantly affected leaf blade photosynthetic capacity, plant growth, and biomass distribution of M. oleifera. Low heavy metal stress enhanced photosynthetic capacity, while high concentration inhibited it. The growth parameters such as plant height, ground diameter, root length, and root diameter of M. oleifera were all negatively affected, with such inhibitory effects being gradually strengthened with increasing stress. M. oleifera  allocated more biomass into belowground as the stress increased. During the remediation process, M. oleifera allocated more heavy metals to belowground biomass. In addition, among the four different heavy metals, M. oleifera showed better tolerance to Cu²⁺ and Zn²⁺, and had high enrichment in Cd²⁺ and Zn²⁺. In conclusion, M. oleifera has good tolerance to mild stress of heavy metals, and could be used as a remediation plant species in areas with mild pollution of combined heavy metals.

Key words: heavy metal, phytoremediation, dry-hot valley, biomass allocation, photosynthesis.