关键词: 恒定增温和逐步增温, 增水, 群落花期物候, 初花期和末花期, 开花功能群, 高寒草原, 青藏高原

Abstract: There is a debate about unmatched results between manipulative warming using constant warming rates every year (CW) and long-term observations warming affect temperature sensitivity of flowering phenology. This may be because long-term observations represent the actual yearly increase in temperature (i.e. a yearly stepwise warming rate per year, SW) which would differ from CW and their effects would be regulated by precipitation alteration. We conducted a warming experiment with CW (temperature increase by +1 °C and sustained this elevated temperature for the duration of the study) and SW (temperature increase by + 0.25 °C progressively each year) with precipitation addition in an alpine grassland for four years. Our results showed that neither warming rate affected community flowering phenology. However, precipitation addition advanced onsets of flowering for early-spring flowering (ESF) and midsummer flowering (MSF) groups, and advanced the end date of flowering for ESF but delayed it for the MSF group. Therefore, flowering duration remained stable for the ESF group and prolonged for the MSF group, and further prolonging the flowering duration of the community. There were no interactions between warming rates and precipitation addition on the community’s flowering phenology. A severe drought in a year significantly decreased the maximal number of community flowers in the following year. Therefore, a change in precipitation has a greater effect than warming on the community flowering phenology in the semi-arid alpine grassland.

Key words: constant and stepwise warming, precipitation addition, flowering phenology of Kobresia pygmaea community, onset and end date of flowering, flowering functional groups, alpine grasslands, Tibetan Plateau