Data from: Experimental icing affects growth, mortality, and flowering in a high Arctic dwarf shrub

Effects of climate change are predicted to be greatest at high latitudes, with more pronounced warming in winter than summer. Extreme mid-winter warm spells and heavy rain-on-snow events are already increasing in frequency in the Arctic, with implications for snow-pack and ground-ice formation. These may in turn affect key components of Arctic ecosystems. However, the fitness consequences of extreme winter weather events for tundra plants are not well understood, especially in the high Arctic. We simulated an extreme mid-winter rain-on-snow event at a field site in high Arctic Svalbard (78°N) by experimentally encasing tundra vegetation in ice. After the subsequent growing season, we measured the effects of icing on growth and fitness indices in the common tundra plant, Arctic bell-heather (Cassiope tetragona). The suitability of this species for retrospective growth analysis enabled us to compare shoot growth in pre and postmanipulation years in icing treatment and control plants, as well as shoot survival and flowering. Plants from icing treatment plots had higher shoot mortality and lower flowering success than controls. At the individual sample level, heavily flowering plants invested less in shoot growth than nonflowering plants, while shoot growth was positively related to the degree of shoot mortality. Therefore, contrary to expectation, undamaged shoots showed enhanced growth in ice treatment plants. This suggests that following damage, aboveground resources were allocated to the few remaining undamaged meristems. The enhanced shoot growth measured in our icing treatment plants has implications for climate studies based on retrospective analyses of Cassiope. As shoot growth in this species responds positively to summer warming, it also highlights a potentially complex interaction between summer and winter conditions. By documenting strong effects of icing on growth and reproduction of a widespread tundra plant, our study contributes to an understanding of Arctic plant responses to projected changes in winter climatic conditions.气候变化的影响预计在高纬度地区（high latitudes）最为显著，冬季增温幅度较夏季更为突出。当前北极地区的隆冬暖期（mid-winter warm spells）与雪上强降雨事件（heavy rain-on-snow events）的发生频率正逐步升高，这类事件会对积雪（snow-pack）与地面冰的形成产生干扰，进而影响北极生态系统的关键组成部分。不过，极端冬季天气事件对苔原植物（tundra plants）适合度的影响机制尚未得到充分阐明，在高北极（high Arctic）区域这一问题尤为突出。我们在位于高北极地区的斯瓦尔巴群岛（Svalbard，78°N）的野外样地中，模拟了一次极端隆冬雪上强降雨事件，通过实验手段将苔原植被冰封包裹于冰层之中。在后续生长季结束后，我们测定了冰层胁迫对常见苔原植物北极岩须（Arctic bell-heather, Cassiope tetragona）生长与适合度指标的影响。该物种适用于回顾性生长分析（retrospective growth analysis），这使得我们可以对比冰层处理组与对照组植株在实验处理前后的枝条生长情况，同时还能统计枝条存活率与开花表现。相较于对照组，冰层处理样地内的植株枝条死亡率更高，开花成功率更低。在个体样本层面，开花旺盛的植株在枝条生长上的资源投入低于不开花植株，而枝条生长与枝条死亡率呈正相关关系。与预期相悖的是，冰层处理植株中未受损伤的枝条展现出更强的生长能力。这说明在植株遭受损伤后，地上部分的资源会被重新分配至剩余为数不多的未受损分生组织（meristems）中。我们在冰层处理植株中观测到的枝条生长增强现象，对基于北极岩须（Cassiope tetragona）回顾性分析的气候研究具有参考价值。由于该物种的枝条生长对夏季增温（summer warming）呈正向响应，这也凸显了夏季与冬季气候条件之间可能存在的复杂交互作用。本研究通过记录冰层胁迫对一种广泛分布的苔原植物生长与繁殖的显著影响，为理解北极植物对未来冬季气候条件变化的响应提供了重要的实证依据。