Large-scale warming will alter multiple local climate factors in alpine tundra, yet very few experimental studies examine the combined yet distinct influences of earlier snowmelt, higher temperatures and altered soil moisture on alpine ecosystems. This limits our ability to predict responses to climate change by plant species and communities. To address this gap, we used infrared heaters and manual watering in a fully factorial experiment to determine the relative importance of these climate factors on plant flowering phenology, and response differences among plant functional groups. Heating advanced snowmelt and flower initiation, but exposed plants to colder early-spring conditions in the period prior to first flower, indicating that snowmelt timing, not temperature, advances flowering initiation in the alpine community. Flowering duration was largely conserved; heating did not extend average species flowering into the latter part of the growing season but instead flowering was completed earlier in heated plots. Although passive warming experiments have resulted in warming-induced soil drying suggested to advance flower senescence, supplemental water did not counteract the average species advance in flowering senescence caused by heating or extend flowering in unheated plots, and variation in soil moisture had inconsistent effects on flowering periods. Functional groups differed in sensitivity to earlier snowmelt, with flower initiation most advanced for early-season species and flowering duration lengthened only for graminoids and forbs. We conclude that earlier snowmelt, driven by increased radiative heating, is the most important factor altering alpine flowering phenology. Studies that only manipulate summer temperature will err in estimating the sensitivity of alpine flowering phenology to large-scale warming. The wholesale advance in flowering phenology with earlier snowmelt suggests that alpine communities will track warming, but only alpine forbs and graminoids appear able to take advantage of an extended snow-free season.

中文翻译：

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变暖通过较早的融雪作用促进但不会延长高山社区开花

大规模变暖将改变高山苔原的多个局地气候因素，但很少有实验研究检查早期融雪、更高的温度和改变的土壤湿度对高山生态系统的综合而独特的影响。这限制了我们预测植物物种和群落对气候变化的反应的能力。为了解决这一差距，我们在全因子实验中使用红外加热器和手动浇水来确定这些气候因素对植物开花物候的相对重要性，以及植物功能组之间的响应差异。加热促进融雪和开花开始，但在第一朵花前的时期将植物暴露在较冷的早春条件下，表明融雪时间，而不是温度，促进了高山群落的开花开始。花期基本保持不变；加热并没有将平均物种的开花延长到生长季节的后期，而是在加热的地块中开花更早完成。虽然被动加温实验已导致变暖引起的土壤干燥，表明会促进花卉衰老，但补充水并不能抵消加热或延长未加热地块开花引起的平均物种开花衰老的提前，土壤水分的变化对开花的影响不一致期间。功能组对早期融雪的敏感性不同，早季物种的花开始最晚，开花持续时间仅在禾本科和杂草中延长。我们得出的结论是，在辐射加热增加的推动下，较早的融雪，是改变高山开花物候的最重要因素。仅操纵夏季温度的研究将错误地估计高山开花物候对大规模变暖的敏感性。早期融雪在开花物候方面的全面进展表明，高山群落将追踪变暖，但只有高山杂草和禾本科植物似乎能够利用延长的无雪季节。