A global meta-analysis of the effects of plant diversity on biomass partitioning in grasslands

The partitioning
of below- to aboveground biomass is commonly described as the root-to-shoot
ratio (R/S). Although a number of studies have shown that biodiversity can influence
above- and belowground biomass in grasslands at the local and global scale, the
global-scale patterns reflecting how plant diversity affects R/S and the factors
controlling such effects remain unclear. In this study, we explored the global
patterns and associated drivers of biomass partitioning responding to plant
diversity by conducting a meta-analysis of 333 observations from 30 studies in
grasslands worldwide. Overall, plant diversity significantly increased aboveground
biomass (AGB), belowground biomass (BGB), and total biomass (TB), whereas significantly
decreased R/S. The effects of plant diversity on biomass partitioning varied
with experimental types. The effect size for AGB and BGB in the field was
larger than in greenhouse experiments, but the effect size for R/S did not significantly
differ between field and greenhouse experiments. Moreover, there was no
significant relationship between R/S and species richness and experimental
duration in greenhouse experiments. However, the effect size for AGB, BGB, and R/S
increased logarithmically with species richness and experimental duration in
the field experiments. Specifically, the effect size for R/S in the field
experiments switched from negative to neutral as the species richness and
experimental duration increased. Furthermore, the effect size for R/S was positively
correlated with complementary effects of BGB, and it increased logarithmically with
mean annual temperature and precipitation. Structural equation models showed that species
richness, experimental duration, and mean annual temperature impact R/S
indirectly by changing the BGB. Overall, our findings suggest that plant
mixtures invest less in belowground biomass than monocultures, and highlight that
low investment in belowground biomass will disappear gradually over time as
species richness increases.