Allelopathic behaviour of Chinese fir from plantations of different ages

Allelopathy of Chinese fir [Cunninghamia lanceolata (Lamb.) Hook.] has been considered an important cause of productivity decline in successive rotations in Chinese fir plantations. Growth of Chinese fir germinants was measured to understand the allelopathic potential of its leaves and roots, as well as its rhizosphere soil, from different plantation ages. Results show that aqueous extracts from Chinese fir leaves and roots and rhizosphere soil significantly inhibited the growth of germinants. Leaf aqueous extracts showed the strongest inhibitory effects indicating that allelochemicals were produced by the leaf and released into the soil through the roots. Leaf and the root aqueous extracts, as well as the rhizosphere soil, from older Chinese fir plantations exhibited stronger allelopathic potential. Tissue aqueous extract from a 27-year-old Chinese fir showed stronger inhibitory effects on the growth of germinants compared with that from a 3-year-old one. More cyclic dipeptides were found in the leaf aqueous extract; and even more were found in the tissue aqueous extract and in the rhizosphere soil from older plantations. This suggests that more cyclic dipeptides are produced by leaves and released into the soil through the root exudation as Chinese fir plantations increase in age.