Abstract: Phragmites australis (common reed), with extensive distribution and high tolerance to stress, is widely used in pollution remediation. Vegetative propagation is the main way of population maintenance for common reed. It is unclear how Pb pollution would affect clonal growth of reeds under elevated CO₂. To explore responses of clonal reproduction to Pb pollution under elevatedCO₂, we imitated the ambient CO₂ and elevated CO₂ concentrations (380±20 and 760±20 μmol·mol^-1), and Pb pollution (0, 300, 500, 1500, 3000 mg·kg^-1) in phytotron. The number of axillary shoot buds first increased and then decreased with increasing soil Pb concentrations. The number and length of rhizomes, the number of rhizome and apical rhizome buds and total number of buds decreased with increasing soil Pb concentrations. Soil Pb concentrations had no effect on the number of axillary daughter shoots and total number of daughter shoots, but significantly increased the number of apical rhizome daughter shoots and Pb concentrations in organs. Elevated CO₂ increased rhizome growth, the number of each type of buds and daughter shoots, and plant absorption and accumulation of Pb. The concentration of Pb in roots was significantly increased, while the Pb accumulations in rhizomes, steams, and leaves were decreased by elevated CO₂. These results indicated that elevated CO₂ alleviated the negative effects of Pb pollution on clonal growth of common reed, increased clonal propagation and population stabilization through increasing phalanx growth with low cost, guerilla growth by spreading rhizomes, and the effective Pb allocation strategy.

Key words: isotope effect, water vapor trajectory, stable isotope, precipitation, Shaanxi-Gansu-Ningxia region.