Background/Question/Methods Fine roots are key to the biogeochemical cycles of ecosystems, and root traits are critical to ecosystem processes. Despite the ongoing loss of plant diversity, how plant functional dissimilarity affects the plant mixture effects on fine-root biomass and traits remains uncertain. Here we conducted a meta-analysis using 652 paired observations to test the effects of heterogeneous shade and drought tolerance (ST and DT, respectively), heterogeneous plant growth rate (GR), leaf habit dissimilarity (LHD) on fine-root biomass, community-weighted mean rooting depth (WRD), root length density (RLD) and specific root length (SRL) in plant mixtures. Results/Conclusions We found on average (1) fine-root biomass was significantly lower in plant mixtures with contrasting ST than those mixtures without contrasting ST; (2) both the presence of contrasting DT and contrasting GR on fine-root biomass were significantly higher than those in mixtures without the corresponding plant functional dissimilarity, respectively; (3) fine-root biomass and SRL was significantly lower in mixed forests with high LHD than those with low and medium LHD; (4) the effect of plant mixtures on SRL was marginally higher in plant mixtures with contrasting DT than without contrasting DT. Furthermore, the effect of plant mixtures on fine-root biomass decreased over time when contrasting ST present but increased with soil depth when contrasting DT absent. For plant mixtures with contrasting DT, the effect of plant mixtures on RLD increased with soil depth but did not without contrasting DT. We also found the mixture effects on RLD increased with aridity index in plant mixtures with contrasting ST, but decreased without contrasting ST. The mixture effects on SRL decreased with aridity index with contrasting GR but did not without contrasting GR. The effects of plant mixture on WRD both increased with mean annual temperature and aridity index in mixed forests with high LHD but did not with low and medium LHD. Considering the essential role of fine roots on resource uptake, our results suggest the critical importance of plant functional dissimilarity on the decision making of forest management.
