Growth and tissue nitrogen of epiphytic Atlantic bryophytes: effects of increased and decreased atmospheric N deposition

Summary Atlantic bryophytes are of European conservation importance, yet the effect on them of excess atmospheric nitrogen is relatively unknown. This study assesses the effects of increased atmospheric N deposition on the growth and tissue N of epiphytic Atlantic bryophytes, and their potential to recover following a decline in N deposition. The N received in stemflow by bryophytes at two sites was measured and compared to model predictions. Four species of epiphytic bryophytes ( Isothecium myosuroides , Dicranum scoparium , Frullania tamarisci and Ulota crispa ), typical of Atlantic Oak woods, were studied in a 12‐month reciprocal transplant experiment between a pristine Oak woodland receiving a modelled atmospheric deposition of 12 kg N ha −1 year −1 and a polluted one receiving 54 kg N ha −1 year −1 . Tissue N concentration increased and growth declined following an increase in atmospheric N deposition in all species except Ulota crispa . Conversely, tissue N concentration decreased and growth increased in Frullania tamarisci following a decrease in atmospheric N deposition, with similar non‐significant patterns in the other species. The reciprocal transplants indicate a detrimental effect of increased N deposition on the bryophyte species studied. The study indicated recovery following a decrease in atmospheric N deposition, but the responses caused by decreased N deposition were smaller than those due to increased N deposition. This suggests that the time‐scale for recovery of bryophytes from excess N deposition is longer than the timescale of nitrogen impacts.