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 +/- 0.49days degrees 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 +/- 0.83days degrees C-1 during 1980-1994 to -3.30 +/- 0.65days degrees 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.