Warming due to climate change is generally expected to lengthen the growing season in areas of seasonal climate and to advance plant phenology, particularly the onset of leafing and flowering. However, a reduction in aboveground biomass production and reproductive output may occur when warming is accompanied by drought that crosses critical water deficit thresholds. Tracking warmer temperatures has been shown to be species-specific with unknown impacts on community composition and productivity. The variability in species’ ability to leverage earlier leaf unfolding and flowering into increased aboveground net primary production (ANPP) or increased investments into reproductive organs has heretofore been poorly explored. We tested whether phenological sensitivity to temperature, as a result of experimental warming, directly translated into increased plant performance, as measured by ANPP and flower abundance. In order to experimentally simulate climate warming, we translocated a total of 45 intact soil–plant communities downslope along an elevational gradient of 900 m within the European Alps from 1260 to 350 m asl and weekly recorded flower abundance and total green cover as well as cumulative biomass production at peak growing season. We found that advanced phenology at lower elevations was related to increased reproductive performance and conditional on whether they experienced drought stress. While a temperature increase of +1K had positive effects on the amount of reproductive organs for species with accelerated phenology, temperature increase going along with drier conditions resulted in plants being unable to sustain early investment in reproduction as measured by flower abundance. This finding highlights that the interaction of two climate change drivers, warming and drought, can push communities’ past resistance thresholds. Moreover, we detected biotic competition mechanisms and shifts toward forb-depressed states with graminoids best taking advantage of experimentally altered increased temperature and reduced precipitation. Our results suggest that while species may track warmer future climates, concurrent drought events post a high risk for failure of temperature-driven improvement of reproductive performance and biomass production in the European Alps.

中文翻译：

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由于气候变暖，干旱对山地草原的影响抵消了提前开花物候的好处

气候变化引起的变暖通常预计会延长季节性气候地区的生长季节并促进植物物候，特别是叶和开花的开始。然而，当变暖伴随着干旱超过临界缺水阈值时，地上生物量生产和生殖产出可能会减少。已证明追踪更暖的温度是物种特异性的，对群落组成和生产力的影响未知。物种利用较早的叶子展开和开花增加地上净初级生产 (ANPP) 或增加对生殖器官的投资的能力的可变性迄今尚未得到很好的探索。我们测试了作为实验变暖的结果对温度的物候敏感性是否，直接转化为植物性能的提高，如通过 ANPP 和花丰度测量的。为了通过实验模拟气候变暖，我们在欧洲阿尔卑斯山内沿 900 m 海拔梯度从 1260 到 350 m asl 将总共 45 个完整的土壤 - 植物群落转移到下坡，每周记录的花卉丰度和总绿化覆盖以及累积生长旺季的生物质产量。我们发现低海拔的先进物候与繁殖性能的提高有关，并取决于它们是否经历干旱胁迫。虽然温度升高 +1K 对物候加速的物种的生殖器官数量有积极影响，温度升高以及干燥条件导致植物无法维持以花丰度衡量的早期繁殖投资。这一发现突出表明，变暖和干旱这两个气候变化驱动因素的相互作用可以推动社区过去的抵抗阈值。此外，我们检测到生物竞争机制并转变为禾本科植物最好利用实验改变的温度升高和降水减少的抑制状态。我们的研究结果表明，虽然物种可能会追踪未来变暖的气候，但同时发生的干旱事件导致欧洲阿尔卑斯山的温度驱动的繁殖性能和生物量生产失败的风险很高。变暖和干旱可以推动社区过去的抵抗阈值。此外，我们检测到生物竞争机制并转变为禾本科植物最好利用实验改变的温度升高和降水减少的抑制状态。我们的研究结果表明，虽然物种可能会追踪未来变暖的气候，但同时发生的干旱事件导致欧洲阿尔卑斯山的温度驱动的繁殖性能和生物量生产失败的风险很高。变暖和干旱可以推动社区过去的抵抗阈值。此外，我们检测到生物竞争机制并转变为禾本科植物最好利用实验改变的温度升高和降水减少的抑制状态。我们的研究结果表明，虽然物种可能会追踪未来变暖的气候，但同时发生的干旱事件导致欧洲阿尔卑斯山的温度驱动的繁殖性能和生物量生产失败的风险很高。