Variations in the temperature sensitivity of spring leaf phenology from 1978 to 2014 in Mudanjiang, China

Continuous long-term temperature sensitivity (S_T) of leaf unfolding date (LUD) and main impacting factors in spring in the period 1978-2014 for 40 plant species in Mudanjiang, Heilongjiang Province, Northeast China, were analyzed by using observation data from the China Phenological Observation Network (CPON), together with the corresponding meteorological data from the China Meteorological Data Service Center. Temperature sensitivities, slopes of the regression between LUD and mean temperature during the optimum preseason (OP), were analyzed using 15-year moving window to determine their temporal trends. Major factors impacting S_T were then chosen and evaluated by applying a random sampling method. The results showed that LUD was sensitive to mean temperature in a defined period before phenophase onset for all plant species analyzed. Over the period 1978-2014, the mean S_T of LUD for all plant species was - 3.2 ± 0.49 days °C^-1. The moving window analysis revealed that 75% of species displayed increasing S_T of LUD, with 55% showing significant increases (P < 0.05). S_T for the other 25% exhibited a decreasing trend, with 17% showing significant decreases (P < 0.05). On average, S_T increased by 16%, from - 2.8 ± 0.83 days °C^-1 during 1980-1994 to - 3.30 ± 0.65 days °C^-1 during 2000-2014. For species with later LUD and longer OP, S_T tended to increase more, while species with earlier LUD and shorter OP tended to display a decreasing S_T. The standard deviation of preseason temperature impacted the temporal variation in S_T. Chilling conditions influenced S_T for some species, but photoperiod limitation did not have significant or coherent effects on changes in S_T.