RESUMEN

We conducted a 4-year temperature manipulation experiment in a Mongolian grassland to examine the effect of daytime and nighttime warming on grassland recovery after grazing exclusion. After constructing a livestock exclusion fence in the grassland, we established daytime and daytime-and-nighttime warming treatments within the fenced area by a combination of open-top chambers (OTC) and electric heaters. We measured the numbers of plants and aboveground biomass by species after recording percentage vegetation cover every summer for three warming treatments inside the fence-non-warming, daytime warming, and daytime-and-nighttime warming-and for the grassland outside of the fence. OTCs increased daytime temperature by about 2.0 °C, and heaters increased nighttime temperature by 0.9 °C during the growing period. Grazing exclusion had little effect on grassland biomass but reduced the abundance of poorly palatable species and modified plant community composition. Daytime warming decreased soil moisture and lowered aboveground biomass within the fenced grassland but had little effect on plant community composition. Nighttime warming lowered soil moisture further but its effects on grassland biomass and community composition were undetectable. We concluded that recovery of plant biomass in grasslands degraded by grazing would be lowered by future climate warming through soil drying. Because warming had little effect on the recovery of community composition, adverse effects of warming on grassland recovery might be offset by improving plant productivity through mitigation of soil drying by watering. Soil drying due to nighttime warming might have detectable effects on vegetation when warming persists for a long time.