ECOPHYSIOLOGY OF A SNOW-BED BRYOPHYTE KIAERIA-STARKEI DURING SNOWMELTAND UPTAKE OF NITRATE FROM MELTWATER

Snow is a very efficient scavenger of atmospheric pollutants and becau se of the dynamics of snowmelt, much of the pollutant load of a snowpa ck is released at very high concentrations in episodes known as the ac id 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 environ ment is characterized by slightly elevated CO2 concentrations (up to 7 0 mu L/L above ambient), temperatures at and just above 0 degrees C, a nd very low light intensity, with no light penetrating through more th an 50 cm depth of snow. Despite overwinter storage in these conditions , the bryophyte Kiaeria starkei is shown to be capable of photosynthet ic activity immediately after removal of snow cover, and tissue chloro phyll and carbohydrate concentrations increase by 250 and 60%, respect ively, during the 2 weeks thereafter. Comparison of photosynthetic lig ht responses at 5 and 18 degrees C in plants collected from under and out of snow cover demonstrates acclimatization to seasonal environment al change that must enable maximization of growth during the short gro wing season available. Kiaeria starkei is also shown to be capable of nitrate reductase activity even at 2 degrees C and to assimilate more than 90% of the pollutant nitrate coming into contact with it in snowm elt. As nitrate is known to be damaging to bryophytes in excess, this demonstrates a real threat of pollutant deposition to rare snow-bed co mmunities in Scotland today and is an important warning for other regi ons where snow-bed vegetation is important.