恢复生态学组知识库

1. Epiphytes are believed to exhibit minimal internal nitrogen (N) isotopic composition (delta N-15) variation due to severe N limitation in canopy habitats. However, the lack of empirical evidence leaves this question open, complicating the interpretation of foliar delta N-15 in understanding the N economy of epiphytes. 2. Here, the variation in delta N-15 between leaves and roots (triangle N-15(leaf-root)) of 24 epiphyte species from the tropical Xishuangbanna region of southwest China was calculated. Subsequent linear regression and variance decomposition were performed to identify the underlying driving factors. 3. A small triangle N-15(leaf-root) (+0.43 parts per thousand) was observed in epiphytes, which exhibited relatively consistent values across groups (-0.20 parts per thousand to 1.78 parts per thousand) but markedly species-specific values (-2.13 parts per thousand to 2.15 parts per thousand), independently of phylogeny, reflecting the combined effects of external N sources and N acquisition strategies of epiphytes. In particular, positive triangle N-15(leaf-root) values were primarily correlated with leaf N and root carbon (C), while negative triangle N-15(leaf-root) values were associated with leaf C isotopic composition (delta C-13), indicating that distinct N-15 fractionation progresses were at work. 4. Synthesis. These results demonstrate for the first time that triangle N-15(leaf-root) is minimal yet noteworthy within epiphytes compared with soil-rooted plants, reflecting the more severe N stress in the canopy habitats, and suggest that foliar delta N-15-when accounting for N-15 fractionation-can provide valuable insights into the N dynamics of tropical epiphytes.