Physiological and growth responses of the montane bryophyte Racomitrium lanuginosum to atmospheric nitrogen deposition.

•  The effects of nitrogen (N) deposition on the moss Racomitrium lanuginosum within montane heath in Scotland were investigated over 5 yr. •  Permanent field plots were sprayed with KNO3 or NH4 Cl solutions, at doses equivalent to 10 and 40 kg N ha-1  yr-1 , in 3-6 applications each summer. •  Racomitrium growth and cover were severely reduced by N addition, whilst the proportion of dead shoots greatly increased. N dose decreased inducibility of shoot nitrate reductase activity (NRA), suggesting that N saturation of Racomitrium occurred, and caused an increase in potassium leakage. At high dosage, effects of NH4 + were more detrimental than NO3 - . •  Physiological responses to N indicate that the habitat's critical load (CL) is exceeded by addition of 10 kg N ha-1  yr-1 . The differential toxicity of the two forms of N suggests that predominant ion type in deposition should be taken into consideration when CLs are set. In contrast to tissue N, NRA correlated well with shoot growth, and may thus be a useful biological indicator of moss condition.

[1]  J. Pearson,et al.  Short-term physiological responses of mosses to atmospheric ammonium and nitrate , 1997 .

[2]  T. Callaghan,et al.  Growth responses of Polytrichum commune and Hylocomium splendens to simulated environmental change in the sub-arctic. , 1995, The New phytologist.

[3]  I. Alonso,et al.  Effects of nutrient supply, light availability and herbivory on the growth of heather and three competing grass species , 1998, Plant Ecology.

[4]  A. Rowland.  An automated method for the determination of ammonium‐n in ecological materials , 1983 .

[5]  M. B. Usher,et al.  Ecological Change in the Uplands. , 1989 .

[6]  D. Thompson,et al.  Regional and historical variation in the nitrogen content of Racomitrium lanuginosum in Britain in relation to atmospheric nitrogen deposition. , 1994, Environmental pollution.

[7]  I. H. Rorison,et al.  Chemical Analysis of Ecological Materials. , 1974 .

[8]  J. Lee.  Unintentional experiments with terrestrial ecosystems: ecological effects of sulphur and nitrogen pollutants , 1998 .

[9]  Jan G. M. Roelofs,et al.  The effects of air‐borne nitrogen pollutants on species diversity in natural and semi‐natural European vegetation , 1998 .

[10]  J. Grace,et al.  Deposition of fixed atmospheric nitrogen and foliar nitrogen content of bryophytes and Calluna vulgaris (L.) Hull. , 1995, Environmental pollution.

[11]  J. Watkins,et al.  Measuring change in British vegetation. ECOFACT Volume 2 , 1999 .

[12]  J. Rodwell.  Grasslands and montane communities , 1992 .

[13]  T. Callaghan,et al.  Responses of a subarctic dwarf shrub heath community to simulated environmental change , 1998 .

[14]  J. Longhurst,et al.  Orographic enhancement of wet deposition in the United Kingdom: Continuous monitoring , 1995 .

[15]  M. Jones,et al.  The influence of nitrogen deposition, competition and desiccation on growth and regeneration of Racomitrium lanuginosum (Hedw.) brid. , 2002, Environmental pollution.

[16]  S. Woodin,et al.  Impacts of increased nitrogen supply on high Arctic heath: the importance of bryophytes and phosphorus availability. , 2001, The New phytologist.

[17]  A. Farmer,et al.  Impacts of sulphur and nitrogen deposition on sites and species of nature conservation importance in Great Britain , 1993 .

[18]  M. Press,et al.  Responses to Acidic Deposition in Ombrotrophic Mires in the U.K. , 1987 .

[19]  J. Cape,et al.  The influence of altitude on rainfall composition at great dun fell , 1988 .

[20]  D. Read,et al.  The effect of increased deposition of atmospheric nitrogen on Calluna vulgaris in upland Britain , 1999 .

[21]  S. Woodin,et al.  Effects of pollutants in snowmelt on Kiaeria starkei, a characteristic species of late snowbed bryophyte dominated vegetation , 1996 .

[22]  S. Woodin,et al.  Effects of increased temperature, drought and nitrogen supply on two upland perennials of contrasting functional type: Calluna vulgaris and Pteridium aquilinum , 1999 .

[23]  J. Lee,et al.  THE EFFECTS OF NITRATE, AMMONIUM AND TEMPERATURE ON NITRATE REDUCTASE ACTIVITY IN SPHAGNUM SPECIES. , 1987, The New phytologist.

[24]  J. B. Kenworthy,et al.  Chemical Analysis of Ecological Materials. , 1976 .

[25]  M. Press,et al.  Nitrate reductase activity in Sphagnum fuscum in relation to wet deposition of nitrate from the atmosphere , 1985 .

[26]  J. W. Bates.  Bryophyte Biology: Mineral nutrition, substratum ecology, and pollution , 2000 .

[27]  S. Woodin,et al.  Interplay between nitrogen deposition and grazing causes habitat degradation , 2003 .

[28]  S. Caporn,et al.  Ecological effects of atmospheric reactive nitrogen deposition on semi‐natural terrestrial ecosystems , 1998 .

[29]  M. Unsworth,et al.  Pollutant transfer in upland regions by occult precipitation , 1983, Nature.

[30]  G. Stewart,et al.  The deposition of atmospheric ammonia and its effects on plants. , 1993, The New phytologist.

[31]  David Johnson,et al.  The effect of long-term nitrogen additions on the bryophyte cover of upland acidic grasslands , 2000 .

[32]  A. Michelsen,et al.  RESPONSES IN MICROBES AND PLANTS TO CHANGED TEMPERATURE, NUTRIENT, AND LIGHT REGIMES IN THE ARCTIC , 1999 .

[33]  S. Jonasson.  Plant responses to fertilization and species removal in tundra related to community structure and clonality. , 1992 .

[34]  F. Stuart Chapin,et al.  Individualistic Growth Response of Tundra Plant Species to Environmental Manipulations in the Field , 1985 .

[35]  L. E. Lowe,et al.  Application of the Berthelot reaction to the determination of ammonium‐N in soil extracts and soil digests , 1980 .

[36]  R. Wal,et al.  Effects of nitrogen deposition on growth and survival of montane Racomitrium lanuginosum heath , 2002 .

[37]  M. Bell,et al.  Agriculture and Conservation in the Hills and Uplands. , 1989 .

[38]  T. Callaghan,et al.  PLANT COMMUNITY RESPONSES TO SIMULATED ENVIRONMENTAL CHANGE AT A HIGH ARCTIC POLAR SEMI-DESERT , 1998 .