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最为显著，冬季增温幅度较夏季更为突出。北极地区的隆冬暖期与强雪面降雨事件的发生频率已逐年上升，这类事件会对积雪层与地面冰的形成产生干扰，进而可能影响北极生态系统的关键组成组分。然而，目前学界对于极端冬季天气事件给苔原植物带来的适合度后果尚缺乏充分认知，在高北极区域这一问题尤为突出。我们在高北极斯瓦尔巴群岛（78°N）的一处野外样地中，通过实验将苔原植被包裹于冰层之中，模拟了一次极端隆冬雪面降雨事件。在后续生长季结束后，我们测定了结冰处理对常见苔原植物北极铃石楠（Cassiope tetragona）的生长与适合度指标的影响。该物种适用于回溯性生长分析，这使得我们能够对比结冰处理组与对照组植株在处理前后的枝条生长情况，同时还可统计枝条存活率与开花表现。结冰处理样地内的植株枝条死亡率更高，开花成功率则低于对照组。在个体样本层面，开花旺盛的植株相较于不开花植株，在枝条生长上的资源投入更少；而枝条生长与枝条死亡率呈正相关关系。由此可见，与预期相悖的是，结冰处理植株中未受损伤的枝条展现出了更强的生长能力。这表明在遭受损伤后，地上部分的资源会被分配至仅剩的少量未受损分生组织。我们在结冰处理植株中观测到的枝条生长增强现象，对基于北极铃石楠回溯性生长分析的气候研究具有参考意义。由于该物种的枝条生长对夏季增温呈正向响应，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。本研究通过记录结冰事件对一种广泛分布的苔原植物的生长与繁殖的显著影响，有助于加深我们对北极植物响应冬季气候预测变化的理解。