The edaphic factor and orchids: Gymnadenia conopsea from contrasting geologies in the Central Balkans

Two different strategies for the distribution of macro- and trace elements can be observed in the terrestrial orchid Gymnadenia conopsea. Most trace elements are not translocated to the above-ground parts, whereas for macro-elements the trend was reversed, with the highest accumulation in the distal parts of the plants. Edaphic stress is one of the main factors affecting plant fitness, but it is still poorly understood, even in rare plants such as orchids. Gymnadenia conopsea is a terrestrial orchid that grows on different geological substrates, making it a model species for the study of adaptive responses to edaphic factors, including metals in soil. The samples of plant tissues of G. conopsea growing on carbonate, ultramafic and siliceous substrates in Serbia and the associated rhizosphere soil were collected and analysed for elemental concentrations. Two different strategies for the distribution of macro- and trace elements were found, corresponding to the trend generally observed in orchids. Trace elements (As, B, Cr, Co, Fe, Mn, and Ni) remain mainly in the underground organs and only a small proportion is transferred to the shoots. It was the opposite for the macroelements (Ca, Mg, K and P) with the highest accumulation occurred in the leaves and inflorescences. The tolerance of G. conopsea to the different geological substrates results from the moderate metal concentrations in the soils analysed and the exclusion strategy of the species, which is the most common response to metal induced stress in orchids.