Changes in day (maximum temperature, TMAX ) and night temperature (minimum temperature, TMIN ) in the preseason (e.g., winter and spring) may have opposite effects on early phenophases (e.g., leafing and flowering) due to changing requirements of chilling accumulations (CAC) and heating accumulations (HAC), which could cause advance, delay or no change in early phenophases. However, their relative effects on phenology are largely unexplored, especially on the Tibetan Plateau. Here, observations were performed using a warming and cooling experiment in situ through reciprocal transplantation (2008-2010) on the Tibetan Plateau. We found that winter minimum temperature (TMIN ) warming significantly delayed mean early phenophases by 8.60 d/°C, but winter maximum temperature (TMAX ) warming advanced them by 12.06 d/°C across six common species. Thus, winter mean temperature warming resulted in a net advance of 3.46 d/°C in early phenophases. In contrast, winter TMIN cooling, on average, significantly advanced early phenophases by 5.12 d/°C, but winter TMAX cooling delayed them by 7.40 d/°C across six common species, resulting in a net delay of 2.28 d/°C for winter mean temperature cooling. The opposing effects of TMAX and TMIN warming on the early phenophases may be mainly caused by decreased CAC due to TMIN warming (5.29 times greater than TMAX ) and increased HAC due to TMAX warming (3.25 times greater than TMIN ), and similar processes apply to TMAX and TMIN cooling. Therefore, our study provides another insight into why some plant phenophases remain unchanged or delayed under climate change.
Keywords: Tibetan Plateau; asymmetrical temperature change at day and night; flowering functional groups; plant phenology; temperature sensitivity; warming and cooling.
© 2019 by the Ecological Society of America.