Abstract: Continuous plantation of Cunninghamia lanceolata in monoculture leads to the accumulation of allelochemicals in soils, which inhibits the growth of itself and associated tree species. Exploring the effects of biochar addition on the growth of C. lanceolata and Michelia macclurei seedlings in mixture and on soil physicochemical properties can provide a scientific basis for mitigating the allelopathic effect and for improving the management of mixed C. lanceolata plantations. In this study, a pot experiment was conducted with one-year-old C. lanceolata and M. macclurei seedlings in mixture, under four corn-straw-derived biochar application levels (0%, 2%, 4%, and 6% of dry soil mass). The effects of different biochar addition levels on organ biomass, non-structural carbohydrates (NSC), and soil physicochemical properties were evaluated. The results showed that: (1) Biochar application significantly increased soil pH,   available phosphorus, available potassium, soil water content and soil total porosity, while significantly decreased soil bulk density (P<0.05). (2) The total biomass of M. macclurei seedlings under biochar amendment treatments ranged from 13.4 to 19.8 g·plant^-1, which was significantly lower than that of the control (34.7 g·plant^-1). In contrast, the total biomass of C. lanceolata seedlings increased significantly by 26.2% under the 4% biochar treatment (P<0.05). (3) The soluble sugar (SS) and NSC contents were the highest in leaves, accounting for 48.4% and 45.6% of total NSC in C. lanceolata and M. macclurei seedlings respectively, significantly higher than that in other organs (P<0.05). The starch was mainly stored in roots, accounting for 51.2% and 56.4% of the total for C. lanceolata and M. macclurei, respectively. (4) Biochar application significantly reduced SS content in both species, as well as the SS and NSC contents in the stems of C. lanceolata and in the roots and stems of M. macclurei (P<0.05). In conclusion, 4% biochar treatment promoted the growth of C. lanceolata seedlings. C. lanceolata and M. macclurei seedlings adjusted their NSC allocation strategies in response to the variations of soil physicochemical properties and alleviated allelopathic stress. This study highlights the importance of biochar in improving soil environment and mitigating allelopathy, providing a scientific basis for the rational application of biochar in sustainable management of C. lanceolata mixed-species plantations.

Key words: biochar, biomass, soluble sugar, starch, planted forest