What are Backshoots Good For? Seasonal Changes in Mineral, Carbohydrate and Water Content of Different Organs of the Epiphytic Orchid, Dimerandra emarginata

Abstract

The epiphytic orchid, Dimerandra emarginata (G. Meyer) Hoehne, keeps older stems (‘ backshoots’) after the attached foliage dies. I investigated seasonal changes in the water, carbohydrate and nutrient content of these leafless stems along with associated, connected organs for 1 year. Older stems significantly increase the water storage capacity of a plant, allowing it to tolerate long periods of drought. Reduction in total non-structural carbohydrates (TNC) at the beginning of the growing season indicated an important role of carbon stored in older stems for the re-initiation of vegetative growth after the dry season, while the lack of an increase in TNC before fruiting suggests no such role for reproduction. While seasonal fluctuations in water contents and TNC were pronounced, concentrations of nutrients (N, P, K) showed only small seasonal variation in all vegetative organs. Allocation of carbon and nutrients to developing fruits was rather high, exceeding, e.g. 20% of the total plant pool of potassium. This large investment in fruits was derived from all vegetative organs. I conclude that persistent stems serve a crucial function in the water, carbon and nutrient relations of epiphytes such as D. emarginata, which live in habitats where access to water and key nutrients is often severely limited.