Abstract Plant phenological shifts on the Qinghai–Tibetan Plateau (QTP) have been a hot research topic during the recent decade. Most previous studies based on remote sensing data suggest that earlier spring green-up is the main contributor to the prolonged vegetation growing season on the QTP. Given the large uncertainties of satellite-derived phenology, this study collected a large number (1455+ records) of long-term and continuous ground phenological observation data across the QTP. Based on these data, we conducted comprehensive analyses of temporal changes in spring green-up date (GUD), autumn leaf senescence date (LSD), and growing season length (GSL) of herbaceous plants from 1981 to 2017 through ordinary least squares regression and meta-analysis, and evaluated the relative contribution of shifts in GUD and LSD to change in GSL using the C-index. Results showed that the overall trends of GUD, LSD, and GSL insignificantly advanced at a rate of –0.17 days/decade, significantly delayed at a rate of 5.29 days/decade, and significantly lengthened at a rate of 5.46 days/decade, respectively. On average, the relative contribution of LSD shift to GSL change was 69.3% which was more than twice that of GUD shift (30.7%). Therefore, it was mainly the delayed LSD, rather than an advanced GUD, that prolonged GSL of QTP herbaceous plants, which was contrary to the prevailing conclusion reported by studies based on remote sensing data. Besides, among three functional groups of herbaceous plants, we found that change trends and patterns of the growing seasons seemed to be more favorable to the growth of forbs, which might shift community structure and further influence ecosystem function. Our study suggests that the importance of autumn phenology has been underestimated on the QTP, and more attention should be paid to the shift in autumn phenology and its influences on ecosystem structure and function under global warming.

中文翻译：

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延迟秋叶衰老日期延长青藏高原草本植物生长季长度

摘要 青藏高原（QTP）植物物候变化是近十年来的研究热点。以往大多数基于遥感数据的研究表明，早春绿化是青藏高原植被生长季节延长的主要原因。鉴于卫星衍生物候的巨大不确定性，本研究收集了大量（1455+ 条记录）整个青藏高原地区的长期和连续地面物候观测数据。基于这些数据，我们通过普通最小二乘回归对1981-2017年草本植物春季绿化日期（GUD）、秋季叶片衰老日期（LSD）和生长季长度（GSL）的时间变化进行了综合分析，荟萃分析，并使用 C 指数评估 GUD 和 LSD 变化对 GSL 变化的相对贡献。结果显示，GUD、LSD和GSL的总体趋势分别以–0.17天/十年的速度不显着地提前，以5.29天/十年的速度显着延迟，以5.46天/十年的速度显着延长。平均而言，LSD 转变对 GSL 变化的相对贡献为 69.3%，是 GUD 转变（30.7%）的两倍多。因此，主要是延迟的 LSD，而不是提前的 GUD，延长了 QTP 草本植物的 GSL，这与基于遥感数据的研究报告的普遍结论相反。此外，在草本植物的三个功能组中，我们发现生长季节的变化趋势和模式似乎更有利于杂草的生长，这可能会改变群落结构并进一步影响生态系统功能。我们的研究表明，秋季物候对青藏高原的重要性被低估，应更加关注秋季物候变化及其对全球变暖下生态系统结构和功能的影响。