Durio Zibethinuszibethinus Murray)
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TROPICS Vol. 13 (1) Issued October 30, 2003 Diurnal CO2 exchange variation in evergreen leaves of the tropical tree, durian (Durio zibethinuszibethinus Murray) 1)* 2)† 3) 3) Kazuharu OGAWA , Akio FURUKAWA , Ahmad Makmom ABDULLAH and Muhamad AWANG 1)Laboratory of Forest Ecology and Physiology, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya 464-8601, Japan 2)Environmental Biology Division, The National Institute for Environmental Studies, Tsukuba, Ibaraki 305-8506, Japan 3)Department of Environmental Sciences, Universiti Putra Malaysia, 43400 UPM Serdang, Malaysia *Author to whom correspondence should be addressed. †Present address: Department of Biological Sciences, Faculty of Science, Nara Women's University, Nara 630-8506, Japan ABSTRACT Diurnal variation of in situ CO2 exchange was investigated during the stage where young and old leaves co-exist in three shoots of tropical evergreen trees of Durio zibethinus Murray growing in an experimental field of Universiti Putra Malaysia. The quantitative proportion of young to old leaves and specific leaf area differed among the three samples. The dark respiration rates in the nighttime and daytime were related exponentially to air temperature. The Q10 ranged between 1.72 and 1.78 for the nighttime dark respiration, and 2.16 and 4.07 for the daytime dark respiration. The relationship between net photosynthetic rate and photosynthetic photon flux density was graphed using a hyperbolic function, where as the specific leaf area decreased the asymptotic rates tended to decrease. CO2 exchange per day was effected by leaf age. The total dark respiration (sum of nighttime and daytime dark respiration) was high and net photosynthesis was low in the shoot where the proportion of young leaves was high. The photosynthetic efficiency of different aged-leaves, which was defined as the ratio of net photosynthesis to dark respiration, ranged from 32 to 152%. Photosynthetic efficiency was low in the shoot with a high proportion of young leaf area, because of low net photosynthesis and high dark respiration. Characteristics of leaf photosynthesis were discussed with respect to leaf physiology and phenology. Key words: Durio zibethinus Murray, in situ CO2 exchange, photosynthetic production, Q10, young and old leaves. INTRODUCTION CO2 exchange of leaves plays a key role in the carbon economy of woody species. However, the study of photosynthetic characteristics of tropical trees is still fragmentary and in most cases the techniques used for measurements of leaf gas exchange are inadequate, because a lack of leaf temperature control has led to variable results (cf. Bazzaz and Pickett, 1980; Mooney et al., 1980; Medina and Klinge, 1983). Ogawa et al. (1995a) developed an open gas-exchange system which tracked ambient air temperature while continually measuring CO2 gas-exchange of fruits of a tropical evergreen tree, Durio zibethinus Murray. D. zibethinus is well known for its large fruits, which can reach 17 cm in diameter and 384 g dry wt. (Ogawa et al. 1995a). It takes about 4 months for the fruits to mature and fruiting often occurs twice a year (Idris 1990; Smith et al. 1992). Ogawa et al. (1995a) provided experimental evidence that photosynthetic assimilates equivalent to 125% of the fruit dry mass is translocated to the fruit from other organs until fruit maturation (Ogawa et al. 1996). Therefore, it is expected that the photosynthetic production by leaves should be high in D. zibethinus in comparison with woody species bearing smaller fruits. Ogawa et al. (1995b) inferred the photosynthetic production by leaves using phenological information on leaf survival strategies. However, physiological data, such as CO2 exchange, of D. zibethinus leaves is lacking. In this paper, the CO2 measurement system developed by Ogawa et al. (1995a) was used for three shoots of D. zibethinus. The purpose of the measurements was to obtain fundamental information, such as the temperature dependence of respiration and light dependence of photosynthesis, on the basis of the results of diurnal changes in CO2 exchange rate of leaves. New leaves on the evergreen trees of D. zibethinus emerged during the stage of co-existence of newly emerged leaves and old leaves. The quantitative proportions of newly emerged leaves to old leaves differed among the three samples. Therefore, the effect of leaf age on respiration and photosynthesis were assessed. Furthermore, characteristics of photosynthetic production of leaves of D. zibethinus were discussed and compared to published data on photosynthesis and respiration. 18 K. OGAWA, A. FURUKAWA, A. M. ABDULLAH and M. AWANG MATERIALS AND METHODS Plant materials Experiments were conducted on three shoots, sample Nos. 1 and 2 from tree No. 1 and sample No. 3 from tree No. 2 of durian (Durio zibethinus Murray) growing in an experimental field station of University Putra Malaysia (UPM) in Selangor, Malaysia. The sample trees, which were derived from the same clone, were planted widely enough to receive full sunlight. The stem diameter at breast height was 27.4 and 34.1 cm in tree Nos. 1 and 2, respectively. The shoots sampled were located on the lower crown surface, but were exposed to full sunlight. The shoots consisted of ten young and twelve old leaves in sample No. 1, six young and twenty-two old leaves in sample No. 2, and ten young and twenty-four old leaves in sample No. 3. Leaves were classified as young or old leaves according to their appearance, i.e., light green for young and dark green for old leaves. The young leaves were almost fully expanded. Gas measuring apparatus In situ CO2 exchange of a whole shoot was measured with an open gas exchange system (cf. Ogawa et al. 1995a). Each shoot was enclosed in a cylindrical assimilation chamber, 18 cm in height and 33 cm in diameter. The assimilation chamber had a thermomodule and a fan in the lower part with two aluminium fin-plates. The inside wall of the chamber was covered with a transparent FEP Teflon film (Du pont, Wilmington, DE). Air temperature was measured outside and inside the chamber with platinum resistance thermometers. The chamber temperature was adjusted to match the outside temperature using a temperature controller (MC-A04A/S, Koito, Tokyo, Japan). The ambient air was taken 11 m above the ground and passed through two air buffers to stabilize the CO2 concentration. The air was fed into the assimilation chamber at a rate of 5.0 l min-1 with an air flow meter (RK1250, Koflock, Kyoto, Japan) and air pump (DM-707ST, Enomoto, Tokyo, Japan). Before the chamber and ambient air were measured with the infrared gas analyzer (EGA, ADC, Herts, UK), the moisture in the air was removed with a perma-pure drier (ZBJ02502-72P, Fuji Electric, Tokyo, Japan) by pressing the air samples with an air pump (APN-085VX-1, Iwaki, Tokyo, Japan). In addition, the air passing through the perma-pure drier was sent to two glass tubes containing a drying agent of magnesium perchlorate. Sample gases were alternatively drawn into the gas analyzer at three-minute intervals. Switching was done using two solenoidal valves (SAB 352-6-0; CKD, Komaki, Japan) which were controlled with two timers (H3BA; Omron, Kyoto, Japan). The data from the CO2-analyzer and thermometers were recorded with a chart recorder (LR4100, Yokogawa, Tokyo, Japan). The integrated value of photosynthetic photon flux density was measured with two quantum sensors (LI-190SA, Li- Cor, Lincoln, NE), one on the chamber and the other outside the crown. The values were stored in a data logger (LI-1000, Lincoln, NE) at one-hour intervals in August and 30-minute intervals in September. Gas measurement procedures The CO2 exchange was measured continuously for whole days during the periods of August 6 to 10, 1993 for sample No. 1, August 10 to 13 for sample No. 2, and September 17 to 28 for sample No. 3. Dark respiration during the day was measured by covering the assimilation chamber with aluminum foil in the morning, and the measurement was conducted for entire days from August 9 to 10 for sample No. 1, August 12 to 13 for sample No. 2, and September 24 to 28 for sample No. 3. In this study, CO2 exchange rate was calculated for 30-minute intervals using three-minute interval data. Night was defined as the period when the integrated value of photosynthetic photon flux density outside the crown was zero. After the measurement of CO2 exchange, the leaf area of young and old leaves in each shoot was measured with an area meter (AAC-100, Hayashi Denko, Tokyo, Japan). The dry mass of these leaves was determined after oven-drying at 85℃ for 24 h. The quantitative characteristics of the shoots are summarized in Table 1. In this study, rates of photosynthesis and respiration were expressed by leaf area, and the respiration of twigs was disregarded, because the dry mass ratio of leaves to twigs was more than 5.5. Determining the temperature dependence of respiration and light dependence of photosynthesis with curve fitting The dependence of respiration r on temperature θ was graphed using the following exponential equation (eg. Butler & Landsberg 1981; Jarvis & Leverenz 1983; Hagihara & Hozumi 1991; Paembonan et al. 1991): CO2 exchange in tropical evergreen leaves 19 r = r0 exp (kθ) ¸ where r0 and k are coefficients specific to each sample. The temperature coefficient Q10 is commonly used to quantitatively express chemical reactions of biological processes in relation to temperature. The Q10 value indicates how much physiological function increases with a temperature increase of 10℃. The Q10 value is about 2 in physiologically relevant temperature ranges (eg. Negisi 1970, 1977; Landsberg 1986; Fitter & Hay 1987). Considering equation 1, we can estimate the Q10 of respiration as follows: Q10 = exp (10k) ¹ The relationship between the net photosynthetic rate pn and the photosynthetic photon flux density PPFD was graphed using a light response model for photosynthesis (Thornley 1976; Charles-Edwards 1981), º p = bPPFD r n ―――――1+aPPFD － where a, b and r are coefficients specific to each sample.