ObjectiveWe tested the effects of litter extracts from Castanopsis kawakamii natural forest on seed germination and radicle growth of coexistence species Chinese fir (Cunninghamia lanceolate), thus to explore the mechanism for the natural regeneration barrier of C. kawakamii species.

MethodThe litter extracts of C. kawakamii natural forest were used as the source of allelochemicals, and the seeds of coexistence species C. lanceolate were used as the tested seeds. We analyzed the influence of litter extracts of undecomposed (branches, leaves, bark, and nutshells), semi-decomposed and fully decomposed layer with different concentrations on the germination rate, germination potential, germination index and radicle growth of C. lanceolate seeds.

ResultThe undecomposed layer litter extract promoted the germination rate of C. lanceolate at the low concentration, and promoted or weakly inhibited the germination rate at high concentration. The germination potential and germination index were inhibited under each concentration. The litter extracts from semi-decomposed and the fully decomposed layer inhibited the germination index of C. lanceolate seeds, and the inhibition was stronger at the low concentrations (1∶50, 1∶100). The effects of undecomposed litter extracts on the radicle growth of C. lanceolate showed a double concentration effect of “low promotion and high inhibition”, and significant inhibition at high concentration (P < 0.05). At the 18th day under the leaf extract concentration of 1∶100, the radicle length increased by 14.3% compared with control, which significantly promoted the growth of C. lanceolate’s radicle length (P < 0.05). The litter extracts from the semi-decomposed layer promoted the radicle growth of C. lanceolate, but it was not significant. The litter extracts of the fully decomposed layer promoted the growth of C. lanceolate’s radicle length under the concentrations of 1∶5, 1∶10 and 1∶50, and the concentration of 1∶30 showed a significant inhibition (P < 0.05).

ConclusionThe low concentration litter extracts of the C. kawakamii natural forest can generally promote or slightly inhibit the germination of C. lanceolate seed and promote its radicle growth, which promoted the regeneration of C. lanceolate and enhanced the competition between species in the forest, and thus indirectly lead to the suppression of natural regeneration of C. kawakamii.