Objective This research investigates the responses of leaf functional traits in Cunninghamia lanceolata to different mixed planting patterns and the correlation between its growth and leaf functional traits. The study aims to elucidate the growth strategies of C. lanceolata in these mixed-species plantation systems and reveal how the mixing effect influences its growth through changes in leaf functional traits, thereby providing a theoretical basis for selecting broadleaved tree species in mixed plantations.

Method Using five fast-growing broad-leaved trees (Sassafras tzumu, Cinnamomum camphora, Liquidambar formosana, Michelia chapensis, and Michelia macclurei) as mixed species, five mixed patterns of Cunninghamia lanceolata × Sassafras tzumu, Cunninghamia lanceolata × Cinnamomum camphora, Cunninghamia lanceolata × Liquidambar formosana, Cunninghamia lanceolata × Michelia chapensis, and Cunninghamia lanceolata × Michelia macclurei were established, with a pure Cunninghamia lanceolata plantation as the control. The study aimed to analyze the differences in leaf morphological traits, chloroplast pigment content, leaf non-structural carbohydrate content, and leaf nutrient (carbon, nitrogen, phosphorus) contents of C. lanceolata under different mixed patterns, as well as the correlation between its growth traits and leaf functional traits.

Result (1) The leaf length, leaf width, leaf area, leaf thickness, and chloroplast pigment (including chlorophyll a, chlorophyll b, carotenoids, and total chlorophyll) contents of C. lanceolata in mixed forests were significantly higher (P < 0.05) than those in pure plantations, whereas the specific leaf area showed an opposite trend. Among the mixed patterns, the C. lanceolata - L. formosana pattern resulted in the highest values for leaf width, leaf thickness, leaf area, chlorophyll a, chlorophyll b, and total chlorophyll contents in C. lanceolata. (2) The non-structural carbohydrate (NSC) content of C. lanceolata showed highly significant differences across the mixed patterns; however, no discernible pattern was observed in its distribution among them. (3) The leaf nitrogen (N), phosphorus (P), and potassium (K) contents in mixed plantations were significantly higher (P < 0.05) than those in the pure plantation, indicating that mixed patterns can effectively enhance the accumulation of photosynthetic products and nutrient use efficiency in C. lanceolata. (4) During both the growth and non-growth periods, the growth traits of C. lanceolata were generally positively correlated with leaf morphological traits, chloroplast pigment contents, and nutrient contents, but negatively correlated with non-structural carbohydrate contents.

Conclusion The C. lanceolata -broadleaf mixed plantation pattern can significantly influence the leaf functional traits of C. lanceolata, thereby enhancing its growth rate. Among them, the Cunninghamia lanceolata × Liquidambar formosana, demonstrated significant advantages in leaf morphological development and photosynthetic efficiency improvement. The findings of this study provide important theoretical support and practical guidance for the sustainable management of C. lanceolata plantations.