Results

There was a positive relationship between the species richness in mixtures and plant functional dispersion, with the majority of the FDis variations being within two-, three-, and four-species mixtures (P = 0.049; Fig. 3a, Table S3). Although the effects of the tree mixtures on productivity (lnRR) significantly increased with the species richness in mixtures (P < 0.001; Fig. 3b), there were still large variations within two-, three-, and four-species mixtures.
There were significant positive effects of multidimensional FDis on lnRR both across the species richness levels (P < 0.001; Fig. 4a), and within two- and four-species mixtures (P = 0.02,P = 0.004, respectively; Fig. 4a, Table S4). Further, the lnRR increased with the FDis of LNC across species richness levels (P= 0.02; Fig. 4b), as well as within four-species mixtures (P = 0.01, respectively; Fig. 4b). The effects of tree mixtures on productivity also increased with the FDis of SLA (P = 0.01; Fig. 4c) and WD (P = 0.003; Fig. 4d) across the species richness levels; however, they exhibited a significant effect of FDis of WD within only four-species mixtures (P = 0.02; Fig. 4d).
The lnRR also increased with the CWM of the LNC both across the species richness levels (P = 0.04; Fig. 5a) and within two- and four-species mixtures (P = 0.02, P = 0.03, respectively; Fig. 5a, Table S5). The lnRR also increased with the CWM of SLA across the species richness levels (P = 0.11; Fig. 5b) and within four-species richness mixtures (P = 0.04; Fig. 5b). Among the correlated CWM of the WD, LNC, and SLA (Table S6), the CWMs of SLA and WD had weaker impacts on the tree mixture effects on productivity than that of the LNC (Fig. 5c).