Foliar nitrogen as an indicator of nitrogen deposition and critical loads exceedance on a European scale

The foliar N content of bryophytes and Calluna vulgaris (L.) has been shown to be an indicator of atmospheric N deposition in the UK at a regional scale (1000km) and more recently on a smaller scale in the vicinity of intensive livestock farms. This work extends the geographical scale of the relationship between foliar N concentration of Calluna vulgaris and other ericaceous shrubs and N deposition with 2 measurement transects, one extending from northern Finland to southern Norway (2000km) and the other extending from central Sweden to Stockholm, south east Sweden (330km). Included in the second transect is a region of complex terrain in the Transtrand uplands, where the variation in N deposition with altitude and canopy cover was quantified using Pb-210 inventories in organic soil. The relationship between foliar N (F-N) and N deposition was shown to increase linearly with N deposition (N-D) over the range 0.8% N to 1.4% N according to F-N = 0.040N(D) + 0.793 (r(2) = 0.70). The data are entirely consistent with earlier studies which together provide a valuable indicator of critical loads exceedance, the threshold value being approximately 1.5% N, which is equivalent to a N deposition of 20 kg N ha(-1) y(-1).