1980-2018年中国东部主要木本植物展叶始期的温度相关时段变化

木本植物春季展叶始期的年际变化通常受其发生前一段时间的气温影响，这个时段被称作温度相关时段（temperature-relevant period，TRP）。TRP开始时间和长度的变化反映了气候增暖对植物发育过程的影响。利用中国物候网观测数据，分析了1980-2018年中国东部8个代表性站点162种木本植物展叶始期的TRP开始时间、结束时间和长度变化。结果显示：（1）亚热带站点比温带站点木本植物的平均TRP开始时间早约43 d，长度长约13 d。（2）TRP开始时间在温带地区北部（哈尔滨和牡丹江）变化不显著，在南部（北京、西安和民勤）以0.41-0.53 d/a的速度显著提前。在亚热带，除桂林外，其他站点展叶始期TRP长度延长和缩短的物种比例相近。这表明气候增暖对不同站点植物TRP的影响不仅取决于增暖的幅度，还和站点的背景气候条件相关。（3）乔木TRP平均开始时间和结束时间分别比灌木晚6.49 d和3.92 d，TRP长度略短于灌木。这与灌木采取机会主义的生存策略有关，而乔木在春季的展叶期较为保守以降低霜冻风险。（4）无论在亚热带还是温带地区，展叶越早的物种，TRP开始时间越早，长度越短，展叶始期与季前温度的相关性越强。研究结果可为研究气候变化对植物物候的影响及物候模型的发展提供科学参考。

Changes in temperature-relevant period for the leaf unfolding date of main woody plants in eastern China during 1980-2018

The variation in spring leaf unfolding date of woody plants is commonly influenced by air temperature in a prior period, which is called the temperature-relevant period (TRP). The shifts in start and length of TRP reflect how climate warming influence plants development. Using the phenological data from China Phenological Observation Network, our study analyzes the changes in start, end, length, and temperature-phenophase relationship (R_TRP) of TRP for 162 woody plants in 8 representative sites of eastern China during 1980-2018. The following results are drawn. (1) Compared with temperate sites, the mean start and length of TRP in subtropical sites are 43 days earlier and 13 days longer, respectively, which is related to the higher forcing requirement and relative slower temperature accumulation rate during TRP of plants in subtropics. (2) The starts of TRP have changed slightly in the northern part of temperate zone (Harbin and Mudanjiang), but have significantly advanced in the southern part (Beijing, Xi''an and Minqin) at 0.41-0.53 d/a. In subtropical sites, except for Guilin, the proportion of plants showing an extended TRP and a shortened TRP is similar in the other sites. It suggests that the effect of climate warming on the chilling process in different sites not only depends on the magnitude of warming, but also is closely related to the background climatic conditions of the sites. (3) The start and end of TRP for tree species is 6.49 days and 3.92 days later than that of shrubs on average, respectively. The length of TRP for trees is a little shorter than that of shrubs. This is related to the opportunistic survival strategies adopted by shrubs, while trees are more conservative in spring to reduce frost risk. (4) In general, the species with an early leaf unfolding date exhibit an early start and a longer length of TRP, as well as a stronger R_TRP in both temperate and subtropical sites. The results can provide scientific reference for studies about the influence of climate change on plant phenology and the development of phenological models.