The effects of shade on seedlings of Orchis morio and Dactylorhiza fuchsii in chalk and clay soil

Abstract

summaryThe responses of two native British orchids, Orchis morio L. and Dactylorhiza fuchsii (Druce) Soó, to shading were tested using 7‐ and 8‐month‐old symbiotically propagated seedlings. Seedlings were raised in culture, set into tubes of clay and chalk soil and grown under shade screens for 10‐wk in a controlled environment chamber in deep green shade, green shade, neutral shade, and unshaded (photosynthetic photon fluence rates (PPFR) 24, 54, 54 and 225 μmol m−2s−1respectively). The dicotyledonous perennial Leontodon hispidus L. was also tested for comparison. The orchids tolerated shade more than did L. hispidus, in which a decrease in PPFR led to a decrease in d.wt, an increase in specific lead area (SLA) and elongation of the petioles. In O. morio, lower PPFR led to only a slight decrease in d.wt in the most shaded treatment, an increase in SLA similar to that of L. hispidus, and an increase in the vertical inclination of some leaves. In D. fuchsii lower PPFR led to a reduction in d.wt, mainly in the roots at higher, and in the leaves at lower, photon irradiance. A change from neutral to green shade reduced growth in L. hispidus, but had no effect on either orchid. The physiological and ecological implications of shade tolerance in orchid seedlings are discussed.