Abstract Temperature and precipitation are primary regulators of plant phenology. However, our knowledge of how these factors might interact to affect plant phenology is incomplete. The Qinghai-Tibetan Plateau, a cold and high region, has experienced no consistent changes in spring phenology, despite a significant warming trend. We conducted a manipulative experiment of warming and precipitation addition in an alpine meadow on the Qinghai-Tibetan Plateau in 2015 (cold and wet), 2016 (warm and dry) and 2017 (mild and very wet). We found that warming increased annual variability of plant spring phenology. Warming delayed green up of all monitored species in 2016, advanced green up of early flowering species in 2015, and did not alter green up in 2017. For example, green up of the shallow rooted Kobresia pygmaea advanced 8 (± 2) days in 2015 and was delayed by 23 (± 3) days in a dry year (2016) under warming compared with control. Early spring precipitation addition can offset the delaying effects of warming in a dry year on the Qinghai-Tibetan Plateau. Under warming plus precipitation addition, community average green up advanced compared to control plots in 2015 and 2016, and community average flowering advanced for all three years. In 2016, flowering of K. pygmaea (an early flowering species) advanced under warming plus precipitation addition compared to control while flowering of other species did not change. Our results highlight that annual variation of soil moisture condition plays a critical role in determining the magnitude and direction of spring phenology response to warming. We provide insights in how plant spring phenology might change in a warmer future in the presence or absence of precipitation increase.

中文翻译：

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青藏高原中部高寒草甸气候变暖和降水增加相互作用影响植物春季物候

摘要 温度和降水是植物物候的主要调节因子。然而，我们对这些因素如何相互作用以影响植物物候的了解是不完整的。青藏高原为寒高区，春季物候变化不明显，但有明显的增温趋势。我们于2015年（寒冷潮湿）、2016年（温暖干燥）和2017年（温和潮湿）在青藏高原的高寒草甸进行了增温和降水增加的操纵试验。我们发现变暖增加了植物春季物候的年度变异性。2016 年变暖延迟了所有监测物种的绿化，2015 年提前了早花物种的绿化，2017 年没有改变绿化。例如，与对照相比，在变暖的干旱年份（2016 年）中，浅根型 Kobresia pygmaea 的绿化在 2015 年提前了 8（±2）天，并延迟了 23（±3）天。早春降水的增加可以抵消青藏高原干旱年份变暖的延迟效应。在增温加降水条件下，2015 年和 2016 年群落平均绿化较对照地块提前，三年内群落平均开花提前。2016 年，与对照相比，K. pygmaea（一种早花物种）在变暖和降水增加的条件下开花提前，而其他物种的开花没有变化。我们的研究结果强调，土壤水分条件的年度变化在确定春季物候响应对变暖的幅度和方向方面起着关键作用。