Table_3_Spatiotemporal Variation of Osmanthus fragrans Phenology in China in Response to Climate Change From 1973 to 1996.DOCX

Climate change greatly affects spring and autumn plant phenology around the world consequently, and significantly impacts ecosystem function and the social economy. However, autumn plant phenology, especially autumn flowering phenology, has not been studied so far. In this study, we examined the spatiotemporal pattern of Osmanthus fragrans phenology, including both leaf phenology (the date of bud-bust, BBD; first leaf unfolding, FLD; and 50% of leaf unfolding, 50 LD) and flowering phenology (the date of first flowering, FFD; peak of flowering, PFD; and end of flowering, EFD). Stepwise multiple linear regressions were employed to analyze the relationships between phenophases and climatic factors in the long term phenological data collected by the Chinese Phenological Observation Network from 1973 to 1996. The results showed that spring leaf phenophases and autumn flowering phenophases were strongly affected by latitude. BBD, FLD, and 50LD of O. fragrans were delayed by 3.98, 3.93, and 4.40 days as per degree of latitude increased, while FFD, PFD and EFD in O. fragrans advanced 3.11, 3.26, and 2.99 days, respectively. During the entire study period, BBD was significantly delayed across the region, whereas no significant trends were observed either in FLD or 50LD. Notably, all flowering phenophases of O. fragrans were delayed. Both leaf and flowering phenophases negatively correlated with growing degree-days (GDD) and cold degree-days (CDD), respectively. BBD and FLD were negatively correlated with total annual precipitation. In addition to the effects of climate on autumn flowering phenology, we found that earlier spring leaf phenophases led to delayed autumn flowering phenophases. Our results suggest that future climate change and global warming might delay the phenological sequence of O. fragrans. Our findings also advanced the flowering mechanism study of autumn flowering plants, and facilitated the accurate prediction of future phenology and climate change.

气候变化极大地影响全球范围内的春季与秋季植物物候，进而对生态系统功能与社会经济产生显著影响。然而，目前针对秋季植物物候，尤其是秋季开花物候的研究仍较为匮乏。本研究以桂花（Osmanthus fragrans）为研究对象，解析其物候的时空格局，涵盖叶物候与开花物候两类指标：叶物候包括芽萌动期（bud-bust, BBD）、首叶展叶期（first leaf unfolding, FLD）以及50%叶片展叶期（50 LD）；开花物候则包括始花期（first flowering, FFD）、盛花期（peak of flowering, PFD）以及终花期（end of flowering, EFD）。本研究利用中国物候观测网（Chinese Phenological Observation Network）1973年至1996年的长期物候观测数据，采用逐步多元线性回归方法分析物候期与气候因子之间的关联关系。研究结果表明，春季叶物候期与秋季开花物候期均受纬度的显著调控。随着纬度每升高1°，桂花的BBD、FLD与50LD分别延后3.98天、3.93天与4.40天；而其FFD、PFD与EFD则分别提前3.11天、3.26天与2.99天。在整个研究时段内，研究区域内桂花的BBD均呈显著延后趋势，而FLD与50LD则未出现显著变化趋势。值得注意的是，桂花的所有开花物候期均呈延后趋势。叶物候期与开花物候期分别与生长度日（growing degree-days, GDD）和寒冷度日（cold degree-days, CDD）呈显著负相关关系。BBD与FLD还与年总降水量呈显著负相关。除气候因子对秋季开花物候的影响外，本研究还发现，春季叶物候期提前会导致秋季开花物候期延后。本研究结果表明，未来气候变化与全球变暖可能会延缓桂花的物候进程。本研究结果不仅推进了秋季开花植物的开花机制研究，也为未来物候与气候变化的精准预测提供了理论支撑。