EFFECT OF LIGHT INTENSITY ON GROWTH, LEAF PRODUCTION, LEAF LIFESPAN AND LEAF NUTRIENT BUDGETS OF ACACIA MANGIUM, CINNAMOMUM INERS, DYERA COSTULATA, EUSIDEROXYLON ZWAGERI AND SHOREA ROXBURGHII

• Published in: Journal of tropical forest science Vol. 20; no. 3; pp. 218 - 234
• Main Authors: Tong, P. S., Ng, F. S. P.
• Format: Journal Article
• Language: English
• Published: Kuala Lumpur Forest Research Institute Malaysia 01.07.2008
• Subjects: Branches; Forest ecology; Forest growth; Leaves; Luminous intensity; Nutrient uptake; Plants; Seedlings; Trees; Tropical forests
• ISSN: 0128-1283; 2521-9847

Saplings of Acacia mangium, Cinnamomum iners, Dyera costulata, Eusideroxylon zwageri and Shorea roxburghii were grown side by side at 4, 7, 25, 50 and 100% relative light intensities (RLIs) to facilitate comparison under identical soil and climate conditions. The comparisons cover height increment, diameter increment, rate of production of new leaves, leaf lifespan and leaf nutrient content. The study was carried out in just under two years and the best plants grew from 30 cm to over 300 cm tall. Acacia mangium and S. roxburghii grew fastest at 100% RLI. The other three species grew fastest at 25% RLI. In height, A. mangium at 100% RLI grew four times faster than the second best species, S. roxburghii, and 21 times faster than the slowest species, E. zwageri. Leaf lifespan, found to be maximum at 4% RLI, was shortened by a constant amount by each doubling of light intensity. For example, each doubling of light intensity shortened the leaf lifespan of S. roxburghii by 70 days, and that of A. mangium by 40 days. Photo-senescence of leaves is proposed as a mechanism driving phenological events in the non-seasonal humid tropics. Old leaves at the point of shedding had lower NPK contents than newly expanded leaves. The difference is a measure of internal nutrient recycling of NPK. Mg was sometimes internally recycled, sometimes not, while Ca was usually accumulated. In the two fastest-growing species, A. mangium and S. roxburghii, the NPK content in new leaves tended to peak at about 25% RLI while the growth rate reached its maximum at 100%. Leaf nutrient content did not mirror the rate of growth. Acacia mangium had the highest rate of nutrient uptake per growing shoot—10 to 16 times that of S. roxburghii. At 100% RLI it grew fastest, had the shortest leaf lifespan and the highest leaf turnover rate. Anak pokok Acacia mangium, Cinnamomum iners, Dyera costulata, Eusidexylon zwageri dan Shorea roxburghii ditanam sebelah-menyebelah pada keamatan cahaya relatif (RLI) 4%, 7%, 25%, 50% dan 100% untuk memudahkan perbandingan di bawah keadaan tanah dan cuaca yang serupa. Perbandingan meliputi pertambahan ketinggian, pertambahan diameter, kadar pertumbuhan daun baru, usia daun dan kandungan nutrien daun. Kajian dijalankan selama hampir dua tahun. Anak pokok terbaik tumbuh dari 30 cm hingga lebih daripada 300 cm. Acacia mangium dan S. roxburghii tumbuh paling cepat pada 100% RLI. Ketiga-tiga spesies yang lain tumbuh paling cepat pada 25% RLI. Acacia mangium pada 100% RLI tumbuh empat kali lebih tinggi daripada S. roxburghii, iaitu spesies kedua tinggi dan 21 kali lebih tinggi daripada E. zwageri, iaitu spesies yang paling lambat pertumbuhannya. Usia daun adalah maksimum pada 4% RLI. Usia daun dipendekkan pada kadar yang tetap dengan setiap penggandaan keamatan cahaya. Misalnya, dengan setiap penggandaan keamatan cahaya, usia daun dipendekkan 70 hari bagi S. roxburghii dan 40 hari untuk A. mangium. Foto-senesen daun dicadangkan sebagai mekanisme yang mengawal kejadian fenologi di kawasan tropika yang tidak bermusim dan lembap. Daun tua pada masa gugur mempunyai kandungan NPK yang lebih rendah daripada daun baru yang matang. Perbezaannya ialah sukatan kitar semula dalaman untuk NPK. Mg kadang-kadang dikitar semula secara dalaman. Ca biasanya dikumpulkan. Untuk A. mangium dan S. roxburghii yang mempunyai pertumbuhan paling cepat, kandungan NPK dalam daun baru adalah maksimum pada 25% RLI sementara kadar pertumbuhan menjadi maksimum pada 100% RLI. Kandungan nutrien daun tidak mencerminkan kadar pertumbuhan. Acacia mangium mempunyai kadar pengambilan nutrien bagi setiap pucuk yang paling tinggi, iaitu 10 hingga 16 kali berbanding dengan S. roxburghii. Pada 100% RLI, A. mangium tumbuh paling cepat, mempunyai usia daun yang paling pendek dan kadar pertumbuhan daun baru yang paling tinggi.