Divergent responses of reproductive phenology to asymmetric warming: Evidence from a 10-year grassland experiment in the inner mongolian steppe

It is well documented that asymmetric daytime and nighttime warming have profound influences on plant growth and ecosystem carbon cycling of terrestrial ecosystems. However, the effects of long-term asymmetric warming on plant phenology and species-specific responses remain unclear. We conducted a ten-year field experiment with daytime and nighttime warming in a temperate steppe in northern China and examined how species-specific reproductive phenology (RP) of six coexisting herbaceous species responded to asymmetric warming during two time periods: early (2006-2009) and late (2013-2015). Overall, nighttime warming advanced the flowering and fruiting time of early-blooming species by 1.2 and 1.6 days, respectively. The responses of reproductive duration for early-blooming species to nighttime warming were species-specific (-3.6 days for Potentilla bifurca, +1.6 days for Allium bidentatum). Nighttime warming significantly shortened reproductive duration of P. bifurca and advanced the flowering and fruiting time of Heteropappus altaicus during the late period relative to the early period. Such species-specific responses of plant phenology and differences in response to short- vs long-term warming could be ascribed to water deficit and increasing coverage of species during the late period, respectively. The findings highlight the critical role of functional traits in mediating the response and adaptation of plant phenology in temperate grasslands under climate warming.