Multiple global changes drive grassland productivity and stability: A meta-analysis

Temporal stability of primary productivity is the key to stable
provisioning of ecosystem services to human beings. Yet, the effects of
various global changes on grassland stability remain ambiguous. Here, we
conducted a comprehensive meta-analysis based on 1,070 multi-year paired
observations from 173 studies, to examine the impacts of various global
changes on productivity, community stability and plant diversity of
grasslands on a global scale. The global change drivers include nitrogen
(N) addition, phosphorus (P) addition, N & P addition,
precipitation increase, precipitation decrease, elevated CO2, and warming.
Global change drivers generally had stronger impacts on grassland
productivity than on temporal stability, except for precipitation changes.
Community temporal stability was reduced by N addition, N & P
addition, and precipitation decrease, but was increased by precipitation
increase and remained unchanged under P addition, elevated CO2, and
warming. In addition, species richness decreased under N addition, N
& P addition, and precipitation decrease. At the plant functional
group level, N & P addition reduced grasses’ stability and
precipitation increase enhanced forbs’ stability. Nutrient additions
decreased community stability via increasing the inter-annual variation
more than the mean of primary productivity, while precipitation changes
mainly affected community temporal stability via changing mean
productivity. The negative impacts of global change drivers (i.e. N
& P addition, warming) on community temporal stability increased
with the degree of species loss, but decreased with increasing stability
of grasses. Moreover, the negative impacts of nutrient addition and
precipitation decrease on community stability was lessened while the
positive effect of precipitation increase on community stability was
enhanced in grasslands with higher historical precipitation variability,
greater soil fertility, and longer experimental duration. Synthesis. Our
findings demonstrate that N-based nutrient additions and drought
destabilise grassland productivity, while precipitation increase enhances
community stability. Impacts of global changes on community productivity
and stability are mediated by species richness, plant functional group,
site-specific environmental conditions (i.e. climate, soil), and
experimental duration, which deserve more attention in grassland
management practices under future global change scenarios.