Diurnal changes in gas exchange and chlorophyll fluorescence were measured in the top canopy leaves of the tropical rainforest tree species, Macaranga conifera (Zoll.) Muell. Arg. during a drought year. Maximum values of net photosynthetic rate (P(n), 10 &mgr;mol m(-2) s(-1)) and stomatal conductance (g(s), 0.2 mol m(-2) s(-1)) were found in east-facing leaves in early morning. After 1000 h, both P(n) and g(s) decreased. Minimum daytime values of P(n), g(s), and photosystem II (PSII) quantum yield (DeltaF/F(m)') were found in horizontally fixed leaves. At a given electron transport rate through PSII (ETR), P(n) was higher in early morning than at midday, suggesting a high rate of photorespiration at midday. We tested the hypothesis that the effect of low leaf temperature (T(leaf)) on P(n) is significant in the early morning, whereas the effect of low g(s) on P(n) predominates at midday. In the early morning, when T(leaf) was increased from 32 to 38 degrees C by artificial heating, P(n) at a given ETR decreased 29%, suggesting that the low T(leaf) was associated with a high P(n). When T(leaf) at midday was decreased from 37 to 32 degrees C by artificial cooling, P(n) increased 22%, but P(n) at a given ETR was higher in early morning than at midday, even at the same low T(leaf) (32 degrees C). This suggests that the rate of photorespiration was higher at midday than in early morning because low g(s) at midday caused a reduction in leaf intercellular CO(2) concentration. We conclude that low P(n) at midday was the result of both a reduction in the photochemical process and an increase in stomatal limitation.

We tested the hypothesis that, in tropical pioneer tree species, vertical leaf angle contributes to high carbon gain because it minimizes damage caused by high irradiances. Diurnal changes in leaf gas exchange and chlorophyll fluorescence were measured in east-facing (EL), west-facing (WL) leaves, and in leaves artificially held horizontal (HL) in the uppermost canopy of Macaranga conifera (Zoll.) Muell. Arg. Maximum values of net photosynthetic rate (P(n)) for EL and HL reached 12 &mgr;mol m(-2) s(-1), whereas maximum P(n) for WL was only 6 &mgr;mol m(-2) s(-1). Midday depressions of P(n) and stomatal conductance occurred at high photosynthetic photon flux densities (PPFD), especially for HL. Photosystem II quantum yield (DeltaF/F(m)') of HL for a given PPFD at the leaf surface was lower in the afternoon than in the morning. Values of DeltaF/F(m)' for HL measured at dusk were lower than those measured just before dawn, suggesting that HL suffered from high light and heat load. Variations in the morphology and physiology of the canopy leaves were associated with different light environments, and there was circumstantial evidence of a transitional point at a PPFD of about 20-30% of full sunlight. Maximum P(n) and nitrogen (N) content were higher in upper canopy leaves than in lower canopy leaves, and the differences were mainly associated with differences in lamina thickness. We conclude that the vertical leaf angle and thick lamina of the top canopy leaves contributed to enhance total carbon gain of the whole plant.

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This research aimed to evaluate the effects of drought stress on growth and the total flavonoid content of tabat barito plant (Ficus deltoidea Jack). The experiment was conducted in the greenhouse Faculty of Mathematics and Natural Sciences, Mulawarman University, using a completely randomized design consisted of 4 levels drought stress including 100%, 80%, 60%, and 40% field capacity. The F. deltoidea maintained for 9 months old and investigated for the growth parameter (plant height, leaf number, leaf area, the number of branches, stem diameter, and biomass), phytochemical screening, and the total flavonoid content. Drought stress has a significant effect on plant height, the number of branches, stem diameter and biomass. Based on the phytochemical screening, leaf extract of F. deltoidea contained alkaloids, phenolics, flavonoids, steroids, and coumarins. The highest total flavonoid content observed under 40% field capacity (430.77 μg CE mg -1 extract) and the lowest total flavonoid content observed under 100% field capacity (282.05 μg CE mg -1 extract). In general, this results showed that the drought stress motivated a significantly decreased of growth and significantly increased of total flavonoid content of leaves extract. ABSTRAKPenelitian ini bertujuan mengetahui pengaruh perlakuan cekaman kekeringan terhadap pertumbuhan dan kadar flavonoid total tumbuhan tabat barito. Penelitian dilakukan di rumah kaca Laboratorium Fisiologi Tumbuhan, Fakultas Matematika dan Ilmu Pengetahuan Alam, Universitas Mulawarman, menggunakan rancangan acak lengkap yang terdiri dari 4 perlakuan kapasitas lapang air (KL) yaitu: KL 100%, KL 80%, KL 60% dan KL 40%. Setelah tanaman berumur 9 bulan dilakukan pengamatan terhadap peubah pertumbuhan (tinggi tanaman, jumlah daun, luas daun, jumlah cabang, diameter batang, biomassa). Perlakuan cekaman kekeringan berpengaruh nyata terhadap tinggi tanaman, jumlah cabang, diameter batang dan biomassa tanaman. Berdasarkan hasil uji fitokimia ekstrak daun tabat barito mengandung alkaloid, fenolik, flavonoid, steroid dan kumarin. Kadar total flavonoid ekstrak daun tertinggi dihasilkan pada perlakuan KL 40% sebesar 430.77 μg Catechin Equivalen (CE) mg -1 ekstrak daun dan berbeda nyata dengan perlakuan KL 100%, 80% dan 60%. Kadar flavonoid total terendah terdapat pada perlakuan KL 100% sebesar 282.05 μg CE mg -1 ekstrak. Secara umum, hasil penelitian ini menunjukkan bahwa perlakuan cekaman kekeringan secara nyata menghambat pertumbuhan dan meningkatkan kadar total flavonoid ekstrak daun tabat barito.Kata kunci: budidaya, cekaman kekeringan, flavonoid, tabat barito (Ficus deltoidea)