高山森林林窗和生长基质对苔藓植物氮和磷含量的影响

苔藓在森林生态系统养分富集和循环方面有重要作用,苔藓植物在氮磷循环中的作用可能受到森林更新和生长基质的影响.为理解苔藓在森林生态系统养分循环中的作用,研究了高山森林不同位置(林窗中心、林窗边缘、林下)和不同生长基质(活立木、倒木、枯立木、大枯枝、根桩、地表)上的苔藓植物氮磷含量.结果表明:地表苔藓氮含量(3.12 mg·g^-1)显著低于其他生长基质上的苔藓,尽管枯立木附生苔藓氮含量高达17.41 mg·g^-1,但倒木、大枯枝、枯立木和活立木苔藓氮含量差异不显著;最高(1.09 mg·g^-1)和最低(0.61 mg·g^-1)的磷含量分别出现在森林地表和枯立木的苔藓,且森林地表的苔藓磷含量显著高于其他生长基质上的苔藓,但倒木、大枯枝、根桩和活立木上的苔藓磷含量差异不显著.林窗位置显著影响了倒木和大枯枝上的苔藓氮、磷含量,林窗内倒木和大枯枝上的苔藓氮、磷含量显著高于林窗边缘.粗木质残体的类型、腐烂等级对苔藓氮、磷含量的影响存在差异,两者交互作用的影响显著;第Ⅴ腐烂等级倒木上的苔藓氮含量显著高于其他腐烂等级;第Ⅲ腐烂等级大枯枝上的苔藓氮含量显著高于其他腐烂等级;第Ⅱ腐烂等级倒木上的苔藓磷含量显著高于其他腐烂等级;第Ⅳ腐烂等级枯立木上的苔藓磷含量显著高于其他腐烂等级.可见,森林林窗更新和粗木质残体腐解过程会影响苔藓植物的氮、磷含量,同时影响森林生态系统的养分循环过程.

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

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 Ⅱ decay class were significantly higher than those with other decay classes. Moreover, the P contents in the epiphytic bryophytes on the snags with Ⅳ 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.