Mixing planting proportions in a plantation affects functional traits and biomass allocation of Cunninghamia lanceolata and Phoebe bournei seedlings

Functional traits of trees are significantly associated with their adaptation strategies and productivity. However, the effects of species composition and mixing proportion on the functional traits of trees grown in mixed plantations have not been studied extensively. In this study, planting experiments (duration about seven months) were used to study variations in functional traits and biomass allocation of Cunninghamia lanceolata (Lamb.) Hook and Phoebe bournei (Hemsley) Yang seedlings in five different mixes (0C:4P, 1C:3P, 1C:1P, 3C:1P, and 4C:0P). Total leaf area per seedling increased in each species as its respective proportion in the mixture decreased. However, the specific leaf area decreased for P. bournei under low percent composition, and the specific leaf area for C. lanceolata differed only marginally among the plantings. The net photosynthetic rates of the two species were higher in the mixed plantings than in their corresponding monocultures, whereas the transpiration rate, stomatal conductance, and instantaneous water use efficiency were not different among the plantings. The average root length and root surface area of C. lanceolata and P. bournei were higher in the mixed plantings than in their monocultures. Specifically, root surface area of C. lanceolate and both root length and surface area of P. bournei increased significantly in the 1C:3P and 2C:2P mixed plantings. Leaf, stem, root, and total dry mass per seedling for C. lanceolata decreased with its increasing percent composition in the mixed plantings, while these variables varied less for P. bournei. The plasticity of biomass allocation was relatively low for both species. Total biomass per planting was higher in the mixed plantings than in the monocultures. Our study indicates that species composition and mixing proportion can considerably affect the functional traits of C. lanceolata and P. bournei. The increase in productivity in the mixed plantings may be partially attributed to low rates of competition between the two species, and future studies should examine the different interspecies relationships. The results of this study can be used to improve plantation productivity and ultimately increase the sustainability of tree products and help to better understand the adaptation strategies of plant coexistence.

Automated summary

Functional traits and biomass allocation of Cunninghamia lanceolata and Phoebe bournei seedlings were studied under different mixing proportions. The study found that species composition and mixing proportion significantly affected the functional traits of the two species, and the increase in productivity in mixed plantations may be due to low rates of competition between the two species.