Sub‐arctic mosses and lichens show idiosyncratic responses to combinations of winter heatwaves, freezing and nitrogen deposition

Abstract

Arctic ecosystems are increasingly exposed to extreme climatic events throughout the year, which can affect species performance. Cryptogams (bryophytes and lichens) provide important ecosystem services in polar ecosystems but may be physiologically affected or killed by extreme events. Through field and laboratory manipulations, we compared physiological responses of seven dominant sub-Arctic cryptogams (three bryophytes, four lichens) to single events and factorial combinations of mid-winter heatwave (6 C for 7 days), re-freezing, snow removal and summer nitrogen addition.We aimed to identify which mosses and lichens are vulnerable to these abiotic extremes and if combinations would exacerbate physiological responses. Combinations of extremes resulted in stronger species responses but included idiosyncratic species-specific responses. Species that remained dormant during winter (March), irrespective of extremes, showed little physiological response during summer (August). However, winter physiological activity, and response to winter extremes, was not consistently associated with summer physiological impacts. Winter extremes affect cryptogam physiology, but summer responses appear mild, and lichens affect the photobiont more than the mycobiont. Accounting for Arctic cryptogam response to multiple climatic extremes in ecosystem functioning and modelling will require a better understanding of their winter eco-physiology and repair capabilities. | INTRODUCTIONThe Arctic is experiencing more extreme weather events due to climate change, causing high mortality rates among species when events surpass survival thresholds (Walsh et al., 2020). Winter, in particular, is expected to experience more extreme events such as rain on snow, heatwaves (extreme winter warming [WW]), ground ice formation and loss of snow cover (Liston & Hiemstra, 2011;Vikhamar-Schuler et al., 2016). Abrupt changes in winter snow cover and depth following winter thaw events (e.g., from À20 C to +5 C in 24 h) affect species survival as snow insulates against temperature extremes (Bokhorst, Pedersen, et al., 2016). In addition, loss of snow cover during a midwinter heatwave can induce physiological activity, while organisms are generally dormant, representing a deacclamation of winter hardiness (Bokhorst et al., 2010;

Macrolichen Communities Depend on Phorophyte in Conguillío National Park, Chile

“…On the other hand, the N exposure of A. araucana showed more fruticose lichens, a result which is in accordance with Woda et al [54], who found abundant fruticose lichens in young Fitzroyetum forests in the temperate rainforests of southern Chile's coastal range Cordillera Pelada, suggesting that fruticose lichens may prefer microhabitats with greater exposure to light, and also showing a higher abundance in stands with higher luminosity. Other abiotic conditions are important to lichens in cold and mountainous habitats, such as hoarfrost and snow, which can negatively affect lichens [55] more in the south than in the north, which receives more sunlight and reaches higher temperatures (Figure 2). These factors affect fruiting lichens more; because of their shape, they accumulate more frost and snow and can become detached or break.…”

Detection of Winter Heat Wave Impact on Surface Runoff in a Periglacial Environment (Ny-Ålesund, Svalbard)

“…Several studies have documented the negative effects of HWs associated with rainfall on small and large herbivores, soil invertebrates, vegetation growth, and reproduction [11,12]. The snow cover loss during a midwinter heat wave can, in fact, trigger physiological activity in organisms that should be generally dormant; this is the case of lichens, generally considered highly resistant to frost and drought, which are physiologically activated, even during the dark polar winters [13], in the case of increased heat and water transfer to the snow-ground interface. In contrast, some other ecological components like mosses, typically growing in habitats with deep snow cover, are more exposed to cold spells when a thinner and less insulating snowpack occurs [11].…”