Effects of a warming gradient on reproductive phenology of Stipa breviflora in a desert steppe

The sensitivity of plant phenology to climate change can be used as the basis for predicting change in plant species' growth and development period as they adapt to gradual increase in atmospheric temperature. However, it is not clear how the reproductive phenology of plants will respond to a continuous increase in temperature gradient, especially when the time series has break points due to interannual change. In this experiment, the flowering phenology of Stipa breviflora, an established species in the desert steppe of Siziwang Banner in northern China, was observed from 2009 to 2019. A no warming treatment and warming treatment (1.3 °C higher than no warming) were applied. Three temperature gradients were defined: the annual average temperature of the 0–10 cm soil layer in the no warming treatment plot from 2009 to 2019 was taken as the average temperature gradient (C2, 5.63 °C ± 1.09); a higher-than-average temperature gradient (C3, 6.93 °C ± 1.34), and a lower than the average temperature gradient (C1, 4.33 °C ± 1.87). The results showed that increasing temperature was an important driving factor that advanced the flowering phenology of S. breviflora. When high temperatures exceed plants’ physiological thresholds (5.63 °C ± 1.09), plants exhibit a temporary delay. Based on a Mann-Kendall test, we found that reproductive phenology was advanced from 2009 to 2015, and delayed by a time break point from 2015 to 2018. After 2018, reproductive phenology continued to be advanced, which once again verified that reproductive phenology would not continue to be advanced in the process of climate warming, but would be temporarily delayed. Therefore, our study reveals the response strategy of S. breviflora to a continuous increase in global atmospheric temperature, and provides a theoretical basis for studying the response mechanism of the desert steppe ecosystem to climate warming. © 2022 The Authors