Regional calcicoly in the moss Rhytidiadelphus triquetrus: survival and chemistry of transplants at a formerly SO2-polluted site with acid soil

The moss Rhytidiadelphus triquetrus has become increasingly restricted to calcareous soils in the countryside around London since the middle of the present century. It has been suggested that this is due either to high SO2 pollution in earlier decades or continuing acidification of precipitation and soils. Intact samples of Rhytidiadelphus carpet (25 X 25 cm) were transplanted from a chalk rendzina at Watlington Hill to clearings in Pleurozium schreberi swards on acid clay soil at Windsor Forest to determine whether conditions are currently unfavourable for Rhytidiadelphus. Some transplants included calcareous soil introduced along with the mosses. Tissue concentrations of exchangeable and intracellular Ca, Mg, K and Al were measured at intervals over 381 d. The Rhytidiadelphus transplants remained healthy after 33 months on acid soil. Shoot exchangeable Mg and K rose rapidly on transplantation to Windsor Forest while exchangeable Ca fell significantly only after 1 year. Intracellular K was unaffected by transplantation. Tissue cation levels were little affected by the nature of the soil beneath the transplants but instead reflected the gross chemistry of the receiver site. This indicates that bryophyte nutrient content is mainly influenced by precipitation and throughfall minerals. Soil chemistry may influence feather mosses via indirect pathways such as leaf leachates or dust. Aluminium levels were near the detection limits and did not change significantly in the transplants. The absence of Rhytidiadelphus from acid soils in Windsor Forest is probably due to historical factors such as a previous episode of high SO2 concentrations.