Grazing and global change factors differentially affect biodiversity-ecosystem functioning relationships in grassland ecosystems

Grazing and global change (e.g., warming, nitrogen deposition and altered
precipitation) both contribute to biodiversity loss and alter ecosystem
structure and functioning. However, how grazing and global change
interactively influence plant diversity, ecosystem productivity, and their
relationship remains unclear at the global scale. Here, we synthesized 73
field studies to quantify the individual and/or interactive effects of
grazing and global change factors on biodiversity-productivity
relationship in grasslands. Our results showed that grazing significantly
reduced plant richness by 3.7% and aboveground net primary productivity
(ANPP) by 29.1%, but increased belowground net primary productivity (BNPP)
by 9.3%. Global change factors, however, decreased richness by 8.0% but
increased ANPP and BNPP by 13.4% and 14.9%, respectively. Interestingly,
the strength of the change in biodiversity in response to grazing was
positively correlated with the strength of the change in BNPP. Yet, global
change flipped these relationships from positive to negative even when
combined with grazing. These results indicate that the impacts of global
change factors are more dominant than grazing on the belowground
biodiversity-productivity relationship, which is contrary to the pattern
of aboveground one. Therefore, incorporating global change factors with
herbivore grazing into Earth system models is necessary to accurately
predict climate-grassland carbon cycle feedbacks in the Anthropocene.