Epiphytes form plant communities that grow on phorophytes (host trees) for physical support, but these arboreal plants do not extract any nutrients directly from the soil or the host. However, the nutrient status of epiphytes and their possible adaptations to nutrient deficiencies in the forest canopy remain unclear. 

In a study published in Ecology and Evolution, researchers from Xishuangbanna Tropical Botanical Garden (XTBG) investigated the ecological stoichiometry of dominant epiphytes to reveal the nutrient status and possible adaptations of the epiphyte community in a subtropical forest canopy. 

The researchers analyzed the C (carbon), N (nitrogen), P (phosphorus), K (potassium), and Ca (calcium) contents and their ratios in the dominant epiphyte species of lichens, bryophytes, ferns, and spermatophyte in Ailao Mountains National Nature Reserve. 

They found that the element contents and ratios of epiphytes at the species level were highly variable. The mean N, P, K, and Ca concentrations in the epiphytes were higher than those in the leaves of the host trees. However, the N and K concentrations in most lichens were lower than those in the leaves of the host trees. 

Moreover, stoichiometric characteristics of epiphytes differed significantly among functional groups. The lichens and the leaves of ferns had lower C concentrations than the bryophytes and the leaves of spermatophytes. The N concentrations were significantly different among the phylogenetic groups (ferns > bryophytes>spermatophytes > lichens). The lowest and highest P concentrations were in the lichens and the leaves of ferns, respectively. The K concentrations in the leaves of ferns and spermatophytes were significantly higher than those in the lichens and bryophytes.  

In addition, compared with terrestrial plants, most epiphytes maintained high nutrient contents during the rainy season. 

"High nutrient contents and various stoichiometric characteristics indicated that epiphytes in the forest canopy might have evolved their own nutritional adaptations, such as high nutrient allocations to the leaves in vascular epiphytes, lower potassium contents in poikilohydric epiphytes, and the trade‐off between stoichiometric plasticity and homeostasis", said Prof. LIU Wenyao, correspondence author of the study.