EFFECTS OF IRRADIANCE AND SPECTRAL QUALITY ON THE SEEDLING DEVELOPMENT OF JELUTONG (DYERA COSTOLATA)

Jelutong [Dyera costulata (Miq.) Hook. f., Apocynaceae] is a along-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. Jelutung [Dyera costulata (Miq.) Hook. f., Apocynaceae] adalah pokok perintis yang panjang hayatnya dan akan menjadi pokok gergasi di hutan hujan di Semenanjung Malaysia dan Sumatra. Kami membuat ujian untuk menentukan tindak balas pertumbuhan, morfologi, anatomi daun, binaan dan fisiologi anak benih jelutung terhadap sinaran yang berbeza (keamatan fluks-foton, 400-700 nm, PFD) dan kualiti spektrum (kuantum "red/far-red," atau R:FR). Anak benih ditanam di enam rawatan yang diulang: (1) cahaya matahari secara terus dan 1.25 R:FR; (2) 40% PFD cahaya dan 1.25 R:FR; (3) 13% PFD dan 1.25 R:FR; (4) 10% PFD dan 0.25 R:FR; (5) 3% PFD dan 1.25 R:FR; dan (6) 3% PFD dan 0.25 R:FR. Berdasarkan pertambahan biqjisim kering, ketinggian akhir, garis pusat kolar, binaan, dan fotosíntesis maksimum, anak benih didapati tumbuh paling cepat dalam 40 % rawatan cahaya matahari, dan sedikit berubah-ubah tindak balasnya terhadap persekitaran yang mendapat PFD rendah dan PFD pertengahan. Kualiti spektrum tidak begitu mempengaruhi pertumbuhan dan perkembangan pokok, tetapi R:FR rendah akan mengurangkan pengagihan daun dan luas daun, serta mengurangkan pertumbu