Host Tree Identity Influences Leaf Nutrient Relations of the Epiphyte Dendrobium guamense Ames.

Epiphytic orchid species grow in stressful conditions that include nutrient deficiency. A greater understanding of the factors that influence epiphytic orchid nutrition may benefit conservationists and horticulturists. Green and senesced leaf nutrient concentrations of the epiphytic Dendrobium guamense were quantified among six host tree species to more fully understand the role of contrasting host identity. Green leaves for D. guamense plants on species with vertical stems contained greater nitrogen, calcium, iron, manganese, zinc, and boron concentrations. Green leaves for D. guamense plants on species with horizontal stems contained greater phosphorus, magnesium, and copper concentrations. Senesced D. guamense leaves followed similar patterns among the host species for all elements except calcium, manganese, and boron. The stoichiometry among green leaf macronutrients indicated nitrogen was most limiting, and the limitation was more severe for plants on horizontal stems. Carbon:nitrogen of senesced leaves indicated D. guamense plants on vertical stems produced higher quality leaf litter, predicting slower decomposition of orchid leaf litter from plants growing on hosts with horizontal stems. The results may improve horticultural decisions to support conservation efforts and show that host identity is a variable that should be more fully studied to understand epiphyte biology.