Plant Activity under Snow and Ice, with Particular Reference to Lichens

Abstract

ABSTRACT. In polar ecosystems primary producers have to cope with the very limited living conditions of the harsh climate. Vascular plants in the Northern Hemisphere extend to the northem-most edges of the continents, but only two taxa are present as far south as the Antarctic Peninsula region in the Southern Hemisphere. Lower plants, lichens in particular, become more important with increasing latitudes and form the dominant element of the Antarctic vegetation. Based on recent investigations and literature, this paper discusses to what extent lichens are better adapted to snow and ice than vascular plants. Vascular plants in high latitudes have high freezing tolerances but are photosynthetically inactive in winter (e.g., evergreen coniferous species), while lichens in a highly freezing-tolerant stage can be active and productive under winter conditions. Vascular plants can be active under snow but have no photosynthesis if the tissue is frozen. Recent in situ measurements indicate that lichens are able to photosynthesize at temperatures below -10°C, apparently in the frozen state. It was also found that photosynthetic CO2 exchange of dry thalli can be activated by snow during frost. Water uptake during winter was also recorded for coniferous trees at the arctic timberline. This uptake may reduce water stress in conifers but apparently has no relevance for metabolic activity. Water uptake from snow and metabolic activity at -10°C are possible for lichens because they are able to photosynthesize at water potentials lower than -20 MPa. Although lichens are adapted to be active in snow at low temperatures, strong light on clear days may inhibit the photosynthetic apparatus. Key words: lichens, higher plants, water relations, life strategies, photosynthetic production, ice, snow RBSUMÉ. Dans les kosystbmes polaires, les producteurs primaires doivent s'accommoder des conditions de vie prkaires dues à la rigueur du climat. L'habitat des plantes vasculaires de l'hkmisphbre borkal s'ktend aux confins nordiques des continents, mais seuls 2 taxons sont prksents à l'extrême sud de la rkgion de la phinsule Antarctique de l'hkmisphbre austral. Plus la latitude augmente, plus les vkgktaux infkrieurs, en particulier les lichens, prennent de l'importance et forment l'klkment dominant de la vkgktation antarctique. S'appuyant sur des recherches et de la documentation rkcentes, cet article discute du degrk auquel les lichens sont mieux adaptks à la neige et à la glace que les plantes vasculaires. Sous de hautes latitudes, ces dernibres ont une tolerance klevke au gel mais sont inactives en hiver sur le plan de la photosynthbe (p. ex., les espkces conifkriennes à feuilles persistantes), alors que les lichens, dans un &at tolkrant trbs bien le gel, peuvent être actifs et productifs en hiver. Les plantes vasculaires peuvent être actives sous la neige, mais elles ne font pas de photosynthbse si le tissu est gelé. Des mesures prises rkcemment in situ rkvblent que les lichens peuvent faire la photosynthbse à des temphatures infkrieures ...

Diurnal changes in photosynthetic activity of the biological soil crust and lichen: Effects of abiotic factors (Petuniabukta, Svalbard)

“…High resistance of lichens from polar regions to partial dehydration of thalli and maintenance of photosynthetic processes is well known and reported (e.g. Kappen 1993, Kappen et al 1995, Henri 2011, Jupa et al 2012, Wu et al 2012, Barták 2014). An interesting effects was observed on August 9 th -10 th , when a dramatic decrease of Φ PSII was found and related to a decrease in air temperature.…”

“…They also show extremely high dehydration and freezing tolerance, and maintenance of full photosynthetic capacity over a wide range of partial dehydration and thallus temperature. (Kappen 1993).In this study, attention is devoted to the comparison of lichen and BSCs photosynthetic activities in relation to environmental factors. To assess of physiologic activity of tested species, we used monitoring of daily changes in Φ PSII .…”

Usnea antarctica, an important Antarctic lichen, is vulnerable to aspects of regional environmental change

“…There 241 were no abundance differences for Collembola and Acari between control plots and OTCs in 242 the moss community (Table 4). itself resulting from the increased insulation and higher temperatures provided by the deeper 298 snow pack (Kappen 1993). Therefore, it is possible that the same mechanism, carbon depletion 299 due to increased winter respiration, also affected U. antarctica inside the OTCs, a proposition 300 which is supported by the CO2 calculations.…”

Habitat stress initiates changes in composition, CO2 gas exchange and C-allocation as life traits in biological soil crusts

“…The possibility of activation by water vapour alone is controversial for lichens in Antarctica. It has been experimentally demonstrated that some Antarctic lichens can reactivate from water vapour alone (Kappen, 1993) and Schroeter and Scheidegger (1995) showed the Antarctic lichen Umbilicaria aprina Nyl. being activated by water uptake in the gaseous phase from snow at subzero temperatures.…”