Ice encapsulation protects rather than disturbs the freezing lichen

Abstract

Arctic and alpine terricolous lichens are adapted to harsh environments and are tolerant to extremely low temperatures when metabolically inactive. However, there are reports indicating that freezing can be lethal to metabolically active lichens. With a projected warmer and more unstable climate, winter precipitation at high latitudes will fall more frequently as rain, causing snowmelt and encapsulating terricolous lichens in ice or exposing them to large temperature fluctuations. Lichens are a major winter food source for reindeer in most parts of the circumpolar region. A laboratory experiment tested how three hydrated reindeer forage lichen species covered by snow, encapsulated in ice, or uncovered responded to storage at freezing temperatures and subsequent warming. Photosynthetic performance (maximal fluorescence of dark-adapted samples and net photosynthetic rates) was significantly lower in lichens not insulated by snow or ice, whereas there were few differences between the snow and ice treatments. It is suggested that snow and ice provide sufficiently moist environments to improve extracellular and reduce intracellular ice nucleation activity. Ice encapsulation, which is often lethal to vascular plants, did not have any negative effects on the studied lichens. The results indicate that complete snow and ice melt followed by refreezing can be detrimental to terricolous lichen ecosystems. Reduced lichen biomass will have a negative effect both on reindeer winter survival and the indigenous peoples who herd reindeer.

Impacts of winter icing events on the growth, phenology and physiology of sub‐arctic dwarf shrubs

“…The majority of studies investigating the impacts of icing events have focussed on agriculturally significant plant species [e.g. wheat, cranberry; Andrews and Pomeroy (1975), Schluter and Crawford (2003)], and of the few studies on arctic and Antarctic plants, all have been conducted as laboratory studies or using pot‐grown plants (Bjerke 2009, Zuniga‐Feest et al 2009) and anoxia (Crawford et al 1994). One of these studies demonstrated the benefits of ice encapsulation on arctic lichens, with ice‐encased lichens showing improved photosynthetic performance compared to lichens left uncovered (Bjerke 2009).…”

Of forest, snow and lichen: Sámi reindeer herders’ knowledge of winter pastures in northern Sweden

“…2). To our knowledge very few research have been carried out on the effects of snow and ice metamorphism on dwarf shrubs and ground lichen and vice et versa (Bjerke, 2009;Tømmervik et al, 2009). It could be important for both reindeer husbandry and forestry if research was developed on this topic.…”

Ecosystem Response to Climatic Change: The Importance of the Cold Season

“…The main food source of these reindeer, lichens, may also be affected by the formation of ice especially if they become encased in ice. Bjerke (2009) performed an icing experiment on three lichens species of importance for reindeer feeding: Cladonia rangiferina, C. stellaris and Flavocetraria nivalis and found that ice encapsulation did not affect these lichens. However, at mild subfreezing (-1.5°C) temperatures, the ice-encased lichens had reduced photosynthetic and chlorophyll fluorescence rates (70 %) suggesting a deterioration of the algal partner.…”