Hu Xiaoli, Zhou Wenlong, Sun Shucun
Department of Biology, School of Life Sciences, Nanjing University, Nanjing, China.
Front Plant Sci. 2020 Sep 4;11:534703. doi: 10.3389/fpls.2020.534703. eCollection 2020.
Climate warming is often seasonally asymmetric with a higher temperature increase toward winters than summers. However, the effect of winter-biased warming on plant reproductive phenology has been seldom investigated under natural field conditions. The goal of this study was to determine the effects of winter-biased warming on plant reproductive phenologies. In an alpine meadow of Tibetan Plateau, we deployed six large (15 m × 15 m × 2.5 m height) open top chambers (three warmed chambers and three non-warmed chambers) to achieve winter-biased warming (i.e., a small increase in annual mean temperature with a greater increase towards winter than summer). We investigated three phenophases (onset and offset times and duration) for both the flowering and fruiting phenologies of 11 common species in 2017 and 8 species in 2018. According to the vernalization theory, we hypothesized that mild winter-biased warming would delay flowering and fruiting phenologies. The data indicated that the phenological responses to warming were species-specific (including positive, neutral, and negative responses), and the number of plant species advancing flowering (by averagely 4.5 days) and fruiting onset times (by averagely 3.6 days) was higher than those delaying the times. These changes were inconsistent with the vernalization hypothesis (i.e. plants need to achieve a threshold of chilling before flowering) alone, but can be partly explained by the accumulated temperature hypothesis (i.e. plants need to achieve a threshold of accumulative temperature before flowering) and/or the overtopping hypothesis (i.e. plants need to reach community canopy layer before flowering). The interspecific difference in the response of reproductive phenology could be attributed to the variation in plant traits including plant height growth, the biomass ratio of root to shoot, and seed mass. These results indicate that a mild winter-biased warming may trigger significant change in plant reproductive phenology in an alpine meadow.
气候变暖通常在季节上是不对称的，冬季升温幅度高于夏季。然而，在自然田间条件下，偏向冬季的变暖对植物繁殖物候的影响鲜有研究。本研究的目的是确定偏向冬季的变暖对植物繁殖物候的影响。在青藏高原的一个高寒草甸中，我们设置了六个大型（15米×15米×2.5米高）开顶式气室（三个增温气室和三个未增温气室），以实现偏向冬季的变暖（即年平均温度略有升高，冬季升温幅度大于夏季）。我们在2017年调查了11种常见物种以及在2018年调查了8种常见物种的开花和结果物候的三个物候期（开始时间、结束时间和持续时间）。根据春化理论，我们假设轻度的偏向冬季的变暖会延迟开花和结果物候。数据表明，物候对变暖的响应具有物种特异性（包括正向、中性和负向响应），提前开花（平均提前4.5天）和结果开始时间（平均提前3.6天）的植物物种数量高于延迟这些时间的物种数量。这些变化仅靠春化假说（即植物在开花前需要达到一定的低温阈值）无法解释，但可以部分地由积温假说（即植物在开花前需要达到一定的积温阈值）和/或超越假说（即植物在开花前需要到达群落冠层）来解释。繁殖物候响应的种间差异可能归因于植物性状的变化，包括株高生长、根冠生物量比和种子质量。这些结果表明，轻度的偏向冬季的变暖可能会引发高寒草甸植物繁殖物候的显著变化。
