哀牢山亚热带森林附生维管植物δ15N特征及分馏效应

δ15N Characteristics and 15N Fractionation Effects of Vascular Epiphytes in Subtropical Forests of Ailao Mountains

摘要:

叶片氮(N)同位素组成(δ¹⁵N)的自然变化被用于研究附生维管植物的N获取和利用策略，但植物在N吸收、转运和同化过程中发生的¹⁵N分馏效应往往会影响基于¹⁵N自然丰度法的研究结果的可靠性。而附生植物体内是否发生¹⁵N分馏效应并导致不同器官间δ¹⁵N差异，以及叶片δ¹⁵N是否能够作为全株δ¹⁵N的可靠代用指标仍不明晰。该研究以哀牢山亚热带常绿阔叶林的附生植物为研究对象，分析了附生植物全株和各器官的δ¹⁵N变化特征，以及器官间δ¹⁵N差值与其他性状的关系。结果表明，附生植物叶片(–3.48‰)、茎(–3.47‰)、根(–2.25‰)的δ¹⁵N均为负值，表明其主要依赖于大气沉降的¹⁵N贫化N源。除长叶粗筒苣苔(Oreocharis longifolia)外，其余附生植物[距药姜(Cautleya gracilis)、棕鳞瓦韦(Lepisorus scolopendrium)、毛唇独蒜兰(Pleione hookeriana)]体内叶-根(∆¹⁵N_leaf–root: –1.23‰)、叶-茎(∆¹⁵N_leaf–stem: –0.62‰)、茎-根(∆¹⁵N_stem–root: –1.10‰)间均表现出显著的N同位素分馏效应，但通常弱于陆生植物。此外，附生植物叶-根¹⁵N分馏值与叶δ¹³C (r=–0.57; P < 0.01)、根δ¹³C (r=–0.57, –0.50; P < 0.05)均显著负相关，可能暗示其对水分亏缺高度敏感。附生维管植物叶片δ¹⁵N与全株δ¹⁵N显著相关(R_adj.²= 0.526，P < 0.01)，证实叶片δ¹⁵N可以作为全株δ¹⁵N的代用指标。这为利用叶片δ¹⁵N探讨附生植物氮获取策略及其生态适应机制提供了重要依据。

Abstract:

The natural variation of nitrogen (N) isotope composition (δ¹⁵N) in leaves has been used to study the N acquisition and utilization strategies of epiphytic vascular plants. However, the ¹⁵N fractionation effect that occurs during N absorption, transport, and assimilation in plants often affects the reliability of research results based on the ¹⁵N natural abundance method. Whether ¹⁵N fractionation occurs in epiphytic plants and leads to δ¹⁵N differences among different organs, as well as whether leaf δ¹⁵N can be used as a reliable proxy for whole-plant δ¹⁵N, remains unclear. This study took epiphytic plants in the subtropical evergreen broad-leaved forest of Ailao Mountain as the research object, analyzed the δ¹⁵N variation characteristics of the whole plant and each organ, and the relationship between the δ¹⁵N difference among organs and other traits. The results showed that the δ¹⁵N of leaves (–3.48‰), stems (–3.47‰), and roots (–2.25‰) of epiphytic plants were all negative, indicating that they mainly relied on ¹⁵N-depleted N sources from atmospheric deposition. Except for Oreocharis longifolia, the other epiphytic plants (Cautleya gracilis, Lepisorus scolopendrium, and Pleione hookeriana) showed N isotope fractionation effects among leaves, stems, and roots (leaf-root: –1.23‰, leaf- stem: –0.62‰, stem-root: –1.10‰), but usually lower than those of terrestrial plants. In addition, the leaf-root ¹⁵N fractionation value of epiphytic plants was significantly negatively correlated with leaf δ¹³C (r=–0.57; P < 0.01) and root δ¹³C (r=–0.57, –0.50; P < 0.05), which may imply their high sensitivity to water deficiency. The δ¹⁵N of epiphytic vascular plant leaves was significantly correlated with whole-plant δ¹⁵N (R_adj.²=0.526, P < 0.01), confirming that leaf δ¹⁵N can be used as a proxy for whole-plant δ¹⁵N. This provides an important basis for using leaf δ¹⁵N to explore the N acquisition strategies and ecological adaptation mechanisms of epiphytic plants.