Ecophysiology of a snow-bed bryophyte Kiaeria starkei during snowmelt and uptake of nitrate from meltwater

Abstract

Snow is a very efficient scavenger of atmospheric pollutants and because of the dynamics of snowmelt, much of the pollutant load of a snowpack is released at very high concentrations in episodes known as the acid flush. The ecological effects of this are largely unknown, but any effects on the bryophyte-dominated vegetation of snow beds will depend in part on the physical environment and physiological state of plants under and just out of snow cover. These factors were investigated at a snow bed in the Cairngorm Mountains, Scotland. The subnivean environment is characterized by slightly elevated CO, concentrations (up to 70 pL/L above ambient), temperatures at and just above O°C, and very low light intensity, with no light penetrating through more than 50 cm depth of snow. Despite overwinter storage in these conditions, the bryophyte Kiaeria starkei is shown to be capable of photosynthetic activity immediately after removal of snow cover, and tissue chlorophyll and carbohydrate concentrations increase by 250 and 60%, respectively, during the 2 weeks thereafter. Comparison of photosynthetic light responses at 5 and 18°C in plants collected from under and out of snow cover demonstrates acclimatization to seasonal environmental change that must enable maximization of growth during the short growing season available. Kiaeria starkei is also shown to be capable of nitrate reductase activity even at 2OC and to assimilate more than 90% of the pollutant nitrate coming into contact with it in snowmelt. As nitrate is known to be damaging to bryophytes in excess, this demonstrates a real threat of pollutant deposition to rare snow-bed communities in Scotland today and is an important warning for other regions where snow-bed vegetation is important.RCsumC : La neige est trks efficace pour capter les polluants atmosphCriques et, i cause de la dynamique de la fonte des neiges, une importante partie de la charge polluante d'un banc de neige est reldchCe avec de fortes teneurs, au cours d'kpisodes connues comme le choc acide. Les effets Ccologiques de ce phCnomkne sont peu connus, mais tout effet des bancs de neige sur une vegetation dominee par des bryophytes dCpendra en partie de l'environnement physique et des Ctats physiologiques des plants situCs sous, et rCcemment CmergCes du couvert de neige. Les auteurs ont examine ces facteurs prks d'un banc de neige situC dans les montagnes Cairngorm, en ~c o s s e . L'environnement subnival se caractkrise par des teneurs 1Cgkrement ClevCe en CO, (jusqu'i 70 pL/L au dessus du milieu ambiant), des temperatures i , ou juste au dessus de, 0°C et une trks faible intensite lumineuse, aucune lumikre n'allant plus bas que 50 cm de neige. Les auteurs montrent que dans ces conditions, en dCpit de rCserves pour l'hiver, la bryophyte Kiaeria starkei est capable d'effectuer la photosynthkse immediatement aprks 1'Climination du couvert de neige et les teneurs des tissus en chlorophylle et en glucides augmentent pour atteindre 250 et 60%, respectivement, au cours des semaines suivantes. Une comparai...

Effects of pollutants in snowmelt onKiaeria starkei, a characteristic species of late snowbed bryophyte dominated vegetation

“…In the 'under snow' plants the chlorophyll a:b ratio increases following exposure to ambient conditions (Fig. 2b), as expected from studies of plants in the field (Woolgrove & Woodin, 1996a). However, the increase observed in plants receiving polluted snowmelt is less rapid than in untreated plants.…”

Photosynthesis of Arctic Evergreens Under Snow: Implications for Tundra Ecosystem Carbon Balance

“…Although bryophytes and lichens reportedly photosynthesize under snow, studies of alpine and arctic vascular plants suggest that the severe subnivean environment prevents significant photosynthetic activity (Tieszen 1974, Kappen 1993, Hamerlynck and Smith 1994. The subnivean environment is characterized by low light levels and temperatures far below freezing for most of the winter (Woolgrove and Woodin 1996). Low temperatures inhibit photosynthesis by increasing the CO 2 diffusion resistances within leaves when solutes freeze (Ϫ5Њ to Ϫ9ЊC) and by directly affecting photosynthetic membrane and biochemical function (Kappen 1993, Larcher 1995.…”

Bud freezing resistance in alpine shrubs across snow depth gradients

“…Interestingly, breaking buds were not observed in any of the study species collected under 1 m of snow in a previous trial experiment that we carried out one week earlier, which rules out the possibility that bud bursting had started already in autumn prior to snow fall. Solar radiation does not penetrate below 0.50 m snow depth (Starr and Oberbauer, 2003;Woolgrove and Woodin, 1996), so photoperiod cues seem unlikely. Further, subnivean temperatures are kept constant around 0 C by the insulating layer of snow (Woolgrove and Woodin, 1996), hampering the occurrence of significant aboveground temperature changes.…”

“…Solar radiation does not penetrate below 0.50 m snow depth (Starr and Oberbauer, 2003;Woolgrove and Woodin, 1996), so photoperiod cues seem unlikely. Further, subnivean temperatures are kept constant around 0 C by the insulating layer of snow (Woolgrove and Woodin, 1996), hampering the occurrence of significant aboveground temperature changes. One of the environmental factors that changed in the few days prior to our sampling was the presence of liquid water in the soil as a result of snowmelt and soil thaw (Fig.…”