Abstract: Aims Root is the key organ for plants to absorb nutrients and water. Investigating the root interactions of mixed-species trees is of great significance to reveal the mechanism driving productivity enhancement in mixed-species stands. Methods A pot experiment was set up by co-planting Cunninghamia lanceolata and Michelia macclurei seedlings. We established three co-planting modes: No separation (NB), 30 μm nylon film separation (MB) and plastic membrane separation (PB), and two controls: C. lanceolata monoculture(MC) and M. macclurei monoculture(MM). The photosynthetic parameters, root morphology and physiological characteristics of seedlings were determined. Important findings The results showed that: 1) the co-planting significantly increased stomatal conductance, transpiration rate and intercellular CO2 concentration (P < 0.05), but did not change the net photosynthetic rate (Pn) of M. macclurei ; 2) Compared with monoculture treatment, mixed planting significantly increased root length, dry mass, surface area, root average diameter, volume, tissue density and root tip number of C. lanceolata (P < 0.05); 3) The root length, root dry weight, specific root length, specific root surface area, root volume and average root diameter of M. macclurei were significantly higher under PB than other treatments (P < 0.05); 4) The mixed treatment significantly reduced the length, surface area and volume of small fine roots (0.0 < D ≤ 0.5mm) of M. macclurei; 5) Under mixed planting treatment, the soluble protein content, malondialdehyde content and antioxidant enzyme activity of C. lanceolata increased significantly. The soluble protein content and malondialdehyde of M. macclurei decreased significantly, but the activity of antioxidant enzymes increased significantly. The findings clarified the effects of interspecific root interactions between C. lanceolata and M. macclurei on the seedling root growth, further revealed mechanisms driving productivity enhancement in mixed-species plantation. This provides empirical evidence for precision silviculture in subtropical mixed plantations.

Key words: mixed forest, root separation, root morphology, root activity, antioxidant enzyme activity