Effects of gap and growth substrate on nitrogen and phosphorus contents of bryophytes in an alpine forest

Abstract

Bryophyte plays an important role in nutrient enrichment and cycling in the forest ecosystems. The role of bryophyte in nitrogen (N) and phosphorus (P) cycles might be affected by forest regeneration and growth substrate. To understand the role of bryophyte in N and P cycling in the forest ecosystem, we measured the contents of N and P in the bryophytes that grew on different positions (gap center, gap edge, and closed canopy) and growth substrates (standing tree, fallen log, snag, large dead branch, stump and forest floor) in an alpine forest ecosystem. The results showed that the N content in the bryophyte on the forest floor was 3.12 mg·g-1, which was significantly lower than those on other growth substrates. Although N content in the bryophyte on the snag reached up to 17.41 mg·g-1, no significant differences of N contents in the bryophytes were observed among standing tree, fallen log, large dead branch and snag. The highest and lowest P contents was 1.09 mg·g-1 in the bryophyte on the forest floor and 0.61 mg·g-1 in the bryophytes on the snag, respectively. Furthermore, P content in the bryophyte on the forest floor was significantly higher than that on other growth substrates, but no significant differences of P contents in the bryophytes were detected among standing tree, fallen log, large dead branch and stump. The gap position significantly affected N and P contents in the bryophytes, with the N and P contents in the bryophytes on fallen log and large dead branch at gap center being significantly higher than those at the gap edge. The effects of coarse woody debris (CWD) on the N and P contents in the bryophyte depended on its types and decay classes, with their interaction having much stronger effects on N and P contents in the bryophytes. The N contents in the epiphytic bryophytes on fallen logs with V decay class were significantly higher than those with other decay classes. Similarly, the N contents in the epiphytic bryophytes on large dead branches with III decay class were significantly higher than those with other decay classes. Meanwhile, the P contents in the bryophytes on fallen logs with 2 decay class were significantly higher than those with other decay classes. Moreover, the P contents in the epiphytic bryophytes on the snags with 4 decay class were significantly higher than those with other decay classes. In conclusion, both forest gap regeneration and CWD decay process can affect the N and P contents in the bryophytes, and thereafter manipulate the nutrient cycles in the forest ecosystems.