Historical nitrogen content of bryophyte tissue as an indicator of increased nitrogen deposition in the Cape Metropolitan Area, South Africa
Faculty of Computing, Health and Science
School of Natural Sciences / Centre for Ecosystem Management
Information on changes in precipitation chemistry in the rapidly expanding Cape Metropolitan Area (CMA) of South Africa is scarce. To obtain a long-term record of N deposition we investigated changes in moss foliar N, C:N ratios and nitrogen isotope values that might reflect precipitation chemistry. Tissue from 9 species was obtained from herbarium specimens collected between 1875 and 2000 while field samples were collected in 2001/2002. There is a strong trend of increasing foliar N content in all mosses collected over the past century (1.32–1.69 %N). Differences exist between ectohydric mosses which have higher foliar N than the mixohydric group. C:N ratios declined while foliar delta-15N values showed no distinct pattern. From relationships between moss tissue N and N deposition rates we estimated an increase of 6–13 kg N ha−1 a−1 since 1950. Enhanced N deposition rates of this magnitude could lead to biodiversity losses in native ecosystems. This study of bryophyte tissue nutrient contents shows a historical increase in N deposition rates to the low nutrient adapted plant biodiversity hotspot in the Western Cape, South Africa.