云南亚热带森林固氮地衣与共存附生植物间的氮转移

Nitrogen transfer from nitrogen-fixing lichen to co-occurring epiphytes in the subtropical forests of Yunnan

关键词:  附生植物, 蓝藻型地衣, 氮转移, ¹⁵N自然丰度法(δ¹⁵N), 养分获取, 哀牢山

Key words:  epiphyte, cyanolichens, nitrogen transfer, δ¹⁵N, nutrient acquisition, Ailao Mountains

摘要:

在养分贫瘠的林冠生境中,附生植物如何获取充足的氮(N)以满足自身生长需求,是附生植物面临的主要挑战之一。蓝藻型地衣类群,具有卓越的生物固氮能力。为探究附生植物能否从共存的固氮地衣中获取N,该文以哀牢山亚热带山地湿性常绿阔叶林系统中的附生植物与固氮地衣为研究对象,通过¹⁵N自然丰度法分析,探讨了二者之间的氮转移及其对附生植物养分变化的影响。结果表明:(1)固氮地衣能够将可观的N转移给附生植物,其对附生苔藓和蕨类的氮贡献分别达到26.18%和35.15%。(2)固氮地衣的存在促进了附生苔藓对磷(P)的获取,显著降低了其N:P值,但对附生蕨类的影响不明显。(3)固氮地衣-附生蕨类的氮转移主要受到固氮地衣生长方位和宿主胸径的影响,而固氮地衣-附生苔藓的氮转移主要受到固氮地衣生长方位和盖度的影响。综上认为,亚热带森林系统中固氮地衣是共存附生植物群落的重要N源,这为解释森林林冠环境附生植物物种多样性分布格局提供了数据支持。

Abstract:

Acquiring sufficient nitrogen(N)to meet requirements for growth is a major challenge for epiphytes living in nutrient-poor canopy habitats. Cyanolichens(lichens that contain cyanobacterial symbionts)can function as the primary participants in biological nitrogen fixation in many terrestrial ecosystems due to their excellent nitrogen-fixing ability, however, it remains unclear whether fixed N from epiphytic cyanolichens can be transferred to neighboring epiphytes. To assess the N contribution of cyanolichens to epiphytes, this study focused on epiphytic ferns, bryophytes and coexisting cyanolichen Lobaria retigera in subtropical montane moist evergreen broad-leaved forests of the Ailao Mountains, Yunnan Province, southwest China. Using ¹⁵N natural abundance analysis, the N transfer between the cyanolichens and epiphytes and its impact on the nutrients of epiphytes were investigated. The results were as follows:(1)Cyanolichens significantly transferred N to epiphytes, contributing 26.18% and 35.15% of N to bryophytes and ferns, respectively.(2)The presence of cyanolichens enhanced the ability of phosphorus(P)acquisition in bryophytes, thereby significantly reducing their N:P ratio, while no significant response was observed in ferns.(3)N transfer from cyanolichens to ferns was primarily influenced by the growth direction of the cyanolichens and the diameter at breast height of the host tree, while N transfer to bryophytes was mainly affected by the growth direction and coverage of the cyanolichens. In conclusion, cyanolichens play a crucial role in supplying N to coexisting epiphyte communities and alleviating N limitation in subtropical forests. This study provides evidence for understanding the formation and maintenance of epiphyte biodiversity in more stressful canopy habitats.