Figure Legends

Figure 1 Global distribution of grassland study sites used in the meta-analysis. Red circles and blue triangles indicate study sites in the field and greenhouse experiments. Source data are provided as a Source Data file.
Figure 2 Comparison of carbon and nitrogen attributes between plant mixtures and monocultures in grasslands. The effects represent the increase or decrease (%) of a given attribute compared to the corresponding mean of monocultures at the mean plant diversity in mixtures (see Methods). Values are mean ± 95% confidence intervals of the percentage effects between the plant mixtures and monocultures. The number of observations for each attribute is displayed in parentheses. Abbreviations: AGB, aboveground biomass; BGB, belowground biomass; TB, total biomass; SCP, soil carbon pool; Rs, soil respiration; Rh, heterotrophic respiration; MB, microbial biomass; FB, fungal biomass; BB, bacterial biomass; ANP, aboveground nitrogen pool; SNP, soil nitrogen pool; SAN, soil ammonium nitrogen; SNN, soil nitrate nitrogen; SNM, soil nitrogen mineralization; SNL, soil nitrogen leaching. Different colors represent different experimental types.
Figure 3 Relationships between experimental age and the response ratios (RR) for carbon and nitrogen attributes in the field experiments. Plots show aboveground biomass (a), belowground biomass (b), total biomass (c), soil carbon pool (d), soil respiration (e), heterotrophic respiration (f), microbial biomass (g), fungal biomass (h), bacterial biomass (i), aboveground nitrogen pool (j), soil nitrogen pool (k), soil ammonium nitrogen (l), soil nitrate nitrogen (m), and soil nitrogen mineralization (n). The size of the bubble is the relative weight of the response ratio (lnRR ) in the random-effects meta-regression. Larger bubbles indicate study outcomes that contributed a greater overall weight in random-effects meta-regression. Solid lines represent significant relationships. Shaded areas show 95% confidence intervals.
Figure 4 Interactions between species richness in plant mixtures and experimental duration in field experiments. Plots show aboveground biomass (a), belowground biomass (b), total biomass (c), soil carbon pool (d), soil respiration (e), heterotrophic respiration (f), microbial biomass (g), fungal biomass (h), bacterial biomass (i), aboveground nitrogen pool (j), soil nitrogen pool (k), soil ammonium nitrogen (l), soil nitrate nitrogen (m), and soil nitrogen mineralization (n). Blue, green, and red lines indicate experimental durations of 1 year, 4 years, and mean experimental duration across all observations; points with different shapes indicate experimental durations. The size of the bubble is the relative weight of the response ratio (lnRR ) in the random-effects meta-regression. Larger bubbles indicate study outcomes that contributed a greater overall weight in the random-effects meta-regression. Shaded areas show 95% confidence interval of the fit.
Figure 5 Relationships between species richness and the response ratios (RR) in the greenhouse experiments. Plots show the aboveground biomass (a), belowground biomass (b), total biomass (c), soil carbon pool (d), soil respiration (e), heterotrophic respiration (f), microbial biomass (g), fungal biomass (h), bacterial biomass (i), aboveground nitrogen pool (j), soil nitrogen pool (k), soil ammonium nitrogen (l), soil nitrate nitrogen (m), and soil nitrogen mineralization (n). The size of the bubble is the relative weight of the response ratio (lnRR ) in the random-effects meta-regression. Larger bubbles indicate study outcomes that contributed a greater overall weight in random-effects meta-regression. Solid lines represent significant relationships. Shaded areas show 95% confidence interval of the fit.
Figure 6 Interactions between species richness in plant mixtures and climate in the field experiments (β5 ). Values are mean ± 95% confidence intervals. Plots show mean annual temperature (a) and precipitation (b). Abbreviations: AGB, aboveground biomass; BGB, belowground biomass; TB, total biomass; SCP, soil carbon pool; Rs, soil respiration; Rh, heterotrophic respiration; MB, microbial biomass; FB, fungal biomass; BB, bacterial biomass; ANP, aboveground nitrogen pool; SNP, soil nitrogen pool; SAN, soil ammonium nitrogen; SNN, soil nitrate nitrogen; SNM, soil nitrogen mineralization. Data for TB comes from only one study site thus the interactive effects of species richness and climate cannot be tested.
Figure 7 Predicted responses of soil carbon (a) and nitrogen (b) pools to a range of plant species richness reduction in grasslands through field experiments. Plots show the plant species richness reduction at 10%, 20%, 40%, and 80%. Lines with different colors represent different species richness levels.