Bryophytes enhance nitrogen content in decaying wood via biological interactions

<p>An increase in the nitrogen (N) content in coarse woody debris (CWD) facilitates its decomposition, affecting the cycling of N and other nutrients in forest ecosystems. Bryophytes may increase the N content by transferring the N in bryophyte tissues to the underlying CWD. This study examined whether and how bryophytes increase N content in the underlying CWD using N-stable isotope ratios (δ¹⁵N) as tracers for N sources. The N content and δ¹⁵N values in CWD with bryophytes were significantly higher than those in CWD without bryophytes. However, the δ¹⁵N values in CWD with bryophytes differed significantly from those in bryophytes on CWD, demonstrating that the N in bryophytes did not cause the increase in N content in CWD. The analyses using δ¹⁵N further indicated that the high N content in CWD with bryophytes may be attributed to increased N supply from wood-decomposing fungi and N-fixing bacteria. This increase in N content may result from the enhanced moisture content in CWD beneath bryophytes, which facilitates the activity of wood-decomposing fungi and N-fixing bacteria. Notably, the influence of bryophytes on the N content in CWD differed between bryophyte life forms: bryophytes that form dense mats increased the N content in CWD, whereas those with loose mats decreased the N content. This difference can be explained by the greater humidity experienced by CWD with bryophytes forming dense mats than that experienced by CWD with bryophytes forming loose mats. Given that the N content in CWD affects the decay processes, the results highlight the importance of biological interactions associated with bryophytes in forest ecosystems.</p>