Physiological Responses of Bryophytes Thuidium tamariscinum and Hylocomium splendens to Increased Nitrogen Deposition

BACKGROUND AND AIMS: Increased levels of nitrogen (N) deposition lead to enhanced N contents and reduced productivity of many bryophyte species. This study aimed at elucidating the mechanisms by which enhanced N uptake may cause growth reduction of bryophytes, focusing on the effects of N addition on carbon (C) metabolism of bryophytes.METHODS: Plantlets of Thuidium tamariscinum and Hylocomium splendens were fertilized with NH4NO3 (N load equalling 30 kg ha^–1 year^–1) for 80 d, including a pulse labelling experiment with 13CO2 to dissect the partitioning of carbon in response to N addition.KEY RESULTS: Growth of T. tamariscinum was not affected by N addition, while H. splendens showed a trend towards growth reduction. Total N concentration was significantly increased by N addition in H. splendens, a significant increase in amino acid-N was found in T. tamariscinum only. In both bryophyte species, a reduction in concentration of lipids, the greatest C storage pool, as well as markedly enhanced turnover rates of C storage pools in fertilized plants were observed.CONCLUSIONS: The results suggest that growth reduction of H. splendens under high levels of N deposition may be caused by enhanced synthesis of N-containing organic compounds, most probably of cell wall proteins. Disturbance of cellular C metabolism, as indicated by enhanced C pool turnover, may further contribute to the decline in productivity of H. splendens.