EFFECTS OF IRRADIANCE AND SPECTRAL QUALITY ON THE SEEDLING DEVELOPMENT OF JELUTONG (<em>DYERA</em> <em>COSTULATA</em>)

Abstract

Jelutong [Dyera costulata (Miq.) Hook. f., Apocynaceae] is a long-lived pioneer tree that eventually becomes a giant emergent in the rain forests of Peninsular Malaysia and Sumatra. We conducted trials to determine responses of growth, morphology, leaf anatomy, architecture and physiology of jelutong seedlings to different irradiances (photon flux density, 400-700 nm, PFD) and spectral qualities (red/far-red quanta, or R:FR). Seedlings were grown in six replicated treatments: (1) direct sunlight and 1.25 R:FR; (2) 40 % solar PFD and 1.25 R:FR; (3) 13 % PFD and 1.25 R:FR; (4) 10 % PFD and 0.25 R:FR; (5) 3 % PFD and 1.25 R:FR; and (6) 3 % PFD and 0.25 R:FR. Based on dry mass increments, final height, collar diameter, architecture, and maximum photosynthesis, seedlings grew most rapidly in the 40 % sunlight treatment, and varied little in response to low- and medium-PFD environments. Spectral quality did not influence growth and development very much, but low R:FR reduced leaf allocation and area, and reduced growth as mass/day. Leaf anatomy and physiology were influenced exclusively by PFD. These results are consistent with observations of jelutong seedlings being shade-tolerant, slow growing, stunted in direct sunlight, and dramatically different to their behaviour in later developmental stages and that of short-lived pioneers.