Abstract: Masson pine seedlings were used as subject in a sand culture experiment to study effect of aluminum (Al)stress on rhizosphere pH, organic acid exudation and Al accumulation of masson pine seedlings. Results show that during the growth ofmasson pine seedlings, rhizosphere pH increased simultaneously with Al concentration rising from 0 to 300μmol·L -1 , but leveled off when Al concentration exceeded 300μmol·L -1. Among the five organic acids ( citric, oxalic, succinic, malic and acetic acids) examined in this experiment, only oxalic and malic acids demonstrated a similar trend, and a positive correlation to rhizosphere pH. The exudation of oxalic andmalic acids plays an important role in variation of rhizosphere pH. Besides, once enteringmasson pine seedlings through their root system, active Al ions accumulated unevenly in the p lant as a result of nutrition and transport mechanism and were significantly higher in roots than in stems and leaves. Al accumulation within the seedlingswas positively correlated with rhizosphere pH, root exudation of oxalic and malic acids when Al concentration in the soilwas under 300μmol·L-1.

Key words: aluminum stress, masson pine ( Pinus massoniana) seedling, root exudation, organic acid, rhizosphere pH