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 (CO2)-C-13 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-contaiming 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.