Epiphytes, which grow non-parasitically on other plants, are thought to experience minimal variation in internal nitrogen (N) isotopic composition (δ15N) due to extreme nitrogen scarcity in the canopy. However, it remains unclear how these canopy-dwelling plants adapt to severe nitrogen limitation in their unique habitat, due to the lack of empirical evidence.
In a study published in Journal of Ecology, researchers from Xishuangbanna Tropical Botanical Garden of the Chinese Academy of Sciences and Lanzhou University demonstrate for the first time that the leaf-root nitrogen isotope is smaller in epiphytes compared to soil-rooted plants, but it still holds ecological significance. Although the degree of nitrogen isotope fractionation between leaves and roots of epiphytes is consistent within the same group, there are significant differences among species.
The study investigated nitrogen isotope fractionation in vascular epiphytes from the tropical forests of Xishuangbanna, Southwest China. Through a meticulous sampling effort involving single-rope climbing, free climbing, and pole pruners, the researchers collected leaf and root samples from 24 epiphyte species. They calculated the difference in δ15N between leaves and roots and conducted statistical analyses to identify key drivers behind the observed patterns.
The results clearly demonstrate that vascular epiphytes exhibit a smaller but noteworthy leaf–root δ15N fractionation compared with soil-rooted plants. The leaf–root δ15N fractionation of epiphytes is species-specific and independent of phylogeny. It varies across habitat scales and taxonomic categories, showing a strong association with the availability of external nitrogen sources or their acquisition efficiencies.
The fractionation values show a marked increase in correlation with leaf and root nitrogen as well as their ratios.It suggests that the internal nitrogen transport and assimilation in epiphytes are strongly influenced by the availability of nitrogen. Additionally, water deficit also significantly affects negative δ15N fractionation.
“Our study demonstrates a significant degree of species specificity in the adaptation of epiphytes to microenvironments and nitrogen cycling. It also highlights the need to account for species specificity when investigating plant nutritional and physiological characteristics ,” said LI Su of XTBG.
First published: 01 August 2025
