Abstract: Effects of climate warming on plant phenology have garnered significant attention in recent decades. However, the distinct and interactive effects of warming during growing and non-growing seasons on plant phenology remain unclear. Here, we aimed to study how seasonal climate warming influences plant phenology in a temperate steppe. Seasonal warming experiment was conducted in Inner Mongolian steppe using open top chambers. Flowering and fruiting times of six dominant species were observed from 2019 to 2020. Interactive effects between growing-season and non-growing-season warming on plant phenology were analyzed using linear mixed-effects models. Growing-season warming advanced the flowering and fruiting onset time, thereby extending the duration of both reproductive phases across the six monitored species. In contrast, non-growing-season warming delayed fruiting onset time by 1.83 days, but did not affect flowering time. Growing-season and non-growing-season warming interactively affected the onset time and duration of fruiting. Specifically, growing-season warming advanced the fruiting onset time by 3.89 days and extended the fruiting duration by 5.76 days in the absence of non-growing-season warming. However, growing-season warming only advanced fruiting onset time by 1.40 days and extended fruiting duration by 1.63 days under non-growing-season warming conditions. These phenological shifts were primarily driven by changes in air temperature and plant height. Our experiment provides clear evidence for the distinct and interactive effects of growing-season and non-growing-season warming on plant phenology, offering valuable insights for predicting future changes in terrestrial ecosystem processes under future global warming scenarios.

Key words: climate warming, flowering time, fruiting time, interactive effects, typical grassland