Data from: Root phenology unresponsive to earlier snowmelt despite advanced aboveground phenology in two subarctic plant communities

Earlier snowmelt at high latitudes advances aboveground plant phenology, thereby affecting water, nutrient and carbon cycles. Despite the key role of fine roots in these ecosystem processes, phenological responses to earlier snowmelt have never been assessed belowground. We experimentally advanced snowmelt in two contrasting plant community types, heath and meadow, in northern Sweden and measured above- and belowground phenology: leaf-out, flowering and fine root growth. We expected earlier snowmelt to advance both above- and belowground phenology, and shrub-dominated heath to be more responsive than meadow. Snow melted on average nine days earlier in the manipulated plots than in controls, and soil temperatures were on average 0.9 C higher during the snowmelt period of three weeks. This resulted in small advances in aboveground phenology, but contrary to our expectations, root phenology was unresponsive with root growth generally starting before leaf-out. These responses to the snowmelt treatment were similar in both plant community types, despite strong differences in dominating plant functional types and root properties, such as root length and turnover. The lack of a response in root phenology, despite warmer soil temperatures and aboveground phenological advances, adds evidence that aboveground plant responses might not be directly translated to belowground plant responses, and that our understanding of factors driving belowground phenology is still limited, although of major importance for water, nutrient and carbon cycling.

高纬度地区的提前融雪会推进地上植物物候，进而影响水循环、养分循环与碳循环。尽管细根（fine roots）在这些生态系统过程中发挥关键作用，但此前从未有研究针对提前融雪对地下物候的影响展开评估。我们在瑞典北部的两种特征迥异的植物群落类型——石楠灌丛（heath）与草甸（meadow）中开展了提前融雪的野外控制实验，观测指标涵盖展叶、开花与细根生长。我们原本假设，提前融雪会同时推进地上与地下物候，且以灌木为主的石楠灌丛的响应程度会高于草甸。实验处理样地的融雪时间较对照组平均提前了9天，且在为期三周的融雪期内，土壤温度平均升高0.9℃。该处理仅带来了地上物候的小幅提前，但与我们的预期相悖的是，地下物候并未出现响应——细根生长通常早于展叶发生。尽管两种植物群落的优势植物功能型（plant functional types）以及根长、根周转率（root turnover）等根系属性存在显著差异，但二者对融雪处理的响应模式却较为相似。尽管土壤温度升高且地上物候出现提前，但地下物候并未产生响应，这进一步佐证了地上植物的响应或许无法直接外推至地下植物的响应；同时也表明，尽管我们对地下物候驱动因素的认知对水循环、养分循环与碳循环至关重要，但目前相关了解仍十分有限。