NAT. NAT. HIST. BUL L. SIAM So c. 49: 295-303 ， 2001 PHOTOSYNTHETIC CAPACITY IN THAI CONIFERS Philip Philip W. Rundel 1，Mark Patterson 2， Kansri Boonpragob 3 and Santi Watthana 4 ABSTRACT Ecophysiological Ecophysiological studies were carried out to detennine photosynthetic capacity and as- sociated sociated gas exch 飢 .ge characteristics of seven species of conifers growing under cornrnon g訂 den conditions in the Queen Sirikit Botanic Garden in the Mae Sa ne Valley 訂 Chi 釦 g Mai ， northem northem Th ailand. Rates of net photosynthesis under conditions of non ・limiting light and water availability availability ranged from a high of 7.9-8.0μmol m- 2・S-I in Pinus kesiya and P. merkusii to a low low of 2.0 in Podocarpus wallichianus. C 訂 bon isotope ratios (o) of -24 .1 %0 in this latter species species indicated a high degree of water use efficiency (WUE) ，while 出巴 two pines ，C ephalot a.x us griffithii griffithii and Dacrydium elatum ， showed low WUE with o values of -29.3 to -30 .4 %0. ・Thai conifers conifers appear to have ecophysiological traits of photosynthetic capacity ，stomatal conduct- 如 ce ，組d water use efficiency comp 訂 'able to those of in North American temperate conifers Our data suggest that inherent limitations in the structural characteristics of the photosynthetic and and water 甘ansport systems in conifers are equally applicable to tropical as well as temperate conifers conifers in mainland Southeast Asia. INTRODUCTION Wh ile there has been a rapidly increasing interest in recent years in the physiological ecology of conifers (SMITH & HINCKLEY ，1995) ， this work has focused almost exclusively on temperate zone conifers ，particularly those in th 巴 genera Pinus ，Abies 叩 d Picea. Relatively little little is known about tropical conifers. Even within a well studied group like the pines in which there are many studies of photosynthetic capacity ， there have been almost no ecophysiological studies of tropical species growing in areas where frost is not an environmental limiting factor (RUNOEL & YOOER ， 1998). Th e conifer flora of 百四land is a small one ，with only 11 species. Six of these 紅 e 加 the the genus Podocarpus sensu latu ，with other genera being Pinus (2 species) ，and Calocedrus ， Da C1 ッdium ，and Cephalot a.x us with a single species each. While all of these species are Southeast Asian endemics in the broad sense ，and occur naturally in lower montane forests of northern and northeastern Thailand ，they represent distinctly different patterns of biogeographic dis 凶 bution. The genus Cephalot ω， us ， for example ， is largely centered in Japan and China ，and reaches its southern limit of occurrence with C. gr 伊 thii in northern IOepartmen 直of Organismic Biology ，E ∞ logy and Evolutio 旧， University of Califomia ， Los An geles ，Califo rnI a USA 90096 (rundelial biolo l! v .ucla.edy) 20epartment 20epartment of Botany ， Oregon State Univ 引 sity ，Corvallis ，01 官gon USA 97331 30 epartm 叩 t of Biology ，Ramkhamhaeng University ， Bangkok 10242 ，Thailand (kansriialr 百m 1. ru.ac 出) 4Queen 4Queen Sirikit Bot 四 ic Gar 台 n， P.O. Box 7，Mae Rim ， Chiang Mai 50180 ，Thailand Received Received 16 J飢 uary 2001; accepted 6 November 200 1. 295 296 PHILIP W. RUNDEL ，MARK PATIERSON ，KANSRI BOONPRAGOB ， AND SANTI WATIHANA Th ailand. In contrast to this pattern ，出 e genus Dac η Idium is largely a southern hemisphere group ， with its primary occuη'ence in southern Chile ，New Ze aland ，Tasmania ，and New Caledonia. Caledonia. It reaches its northern limit of distribution with D. elatum in northernτ 'h ailand. Two tropical pine species in Th ailand ， P. kesiya and P. merkusii ， are widespread species in in Southeast Asia and form 白e most southern occuηence of Pinus 泊 the world ， with P. P. merkusii reaching south of the equator in Sumatra. We 釘 e not aw 釘 'e of any previous studies of photosynthetic capacity in conifer species 合om mainland Southeast Asia. Nor 仕lern Th ailand presents an appropriate 紅 ea to study the ecophysiology ecophysiology of such conifers because all five genera and nine of the 11 Th ai conifers occur occur naturally in this region. Two questions interested us in carry 泊g out 出is research.τ 'h e frrst was: Do tropical conifers conifers growing 泊 a mild ， seasonal monsoon climate have higher photosyn 出etic rates than than temperate conifers? If w 釘 m growing season conditions with abundant water ，low vapor vapor pressure gradients with humid air ， and the absence of a cold season present ideal conditions conditions for conifer growth ， one might expect photosyn 出etic rates higher th 叩 those of temperate temperate conifers. However ， if the structural characteristics of conifer foliage and their associated associated hydraulic systems with fiber tracheids constrain the potential for high rates of carbon carbon fixation ， then comparable rates would be expected. Direct comp 紅 isons within a single single genus can be achieved here with Pinus. τ'h e second question is a special case of the frrs t. Th e genus Podocarpus sensu latu includes a number of species whose foliage is flattened flattened and broad ， with “needles" reaching 5ι70 mm in width in P. wallichian 札Th ere have have been very few reports of photosynthetic rates measured under field conditions for members of the Podocarpaceae. Recent studies with Podocarpus oleifolius in the high An des of Venezuela (CA VIE 阻 S ET AL. ，2000) 佃 d P. coriaceus in the West In dies DUCREY ， 1994) 1994) have reported relatively low rates of maximum net photosynthesis. Do broad-leaved conifers conifers such as these have higher rates of phoωsynthesis than those species of Podocarpus and other co 凶fers with n紅 TOW needles? If such higher rates of photosynthesis exist in broad-leaved broad-leaved Podocarpus ， are they comparable to those of temperate hardwood trees? MATERIALS AND METHODS Study Study Species Trees Trees of seven conifer species were investigated 泊 common g紅 den pl 釦 tings at the Queen Sirikit Botanic Garden in the Mae Sa Valley (ca. 700 m elevation; la t. 18 0 53' N ， long. long. 78 0 56' E) ne 紅 Chiang Mai ， close to the habitat natural of these species. Wi 白白e exception exception of Pinus kes か'a ，which averaged approximately 10m tall ，experimental trees were young individuals 3ー7m in height. Two individuals of each 住民 and multiple leaves on each individual were studied ， with the exception of Podocarpus wallichianus which was represented represented by on1 ya single individual. All study trees were healthy individuals with good growth growth characteristics.τ 'h e general characteristics of the species conifer included for study are are described below. For more information see PHENG 乱 AI (1972) ，KRUSSMAN (1985) ， HIEP & VIDAL (1 996). Cephalotaxus Cephalotaxus griffithii Hook. is a small-to-medium size trl 田. It has stiff needles 2-5 cm 泊 length ， glossy green above but white below. It is distributed from Assam in East PHOTOSYNTHETIC CAPACITY IN THAI CONIFERS 297 India India across North Burma to North and Northeast Thailand where it occurs at 100 0- 1800 m elevation in the lower montane zone of Chiang Mai ， Chiang Rai ， and Loei Provinces ， as as a subcanopy tree in moist evergreen fores t. Dacrydium elatum (Roxb.) Wal l. ex Hook. Typically reaches 35 m in height and 7ι120 cm in diameter. The leaves are small (8-16 mm) and scale-like ， in densely overlapping overlapping a町 angement on the fertile branches. It is reported to occur from East India across across North Burma to Thailand ， and south to Cambodia and Malaysia ， and eastward to the Philippines Philippines and F討i. It occurs at 100 0- 3000 m elevation in North ，Northeast ，East ， and Central Central Th ailand and is typically found along streams on soils derived from sandstone. In Indochina ，this species has an elevational range of 70 0- 2000 m. In the Cardamom and 日ephant Mountains of South Cambodia it occurs in dwarf conifer stands on boggy sites ， frequently frequently with Podocarpus imbricatus. Pinus Pinus kesiya Royale ex Gard. has a spreading or rounded crown ， and needles occur in in bundles of 3 and 100-250 mm in length. Th is species is distributed from Burma across mainland mainland Southeast Asia to the Philippines. In Th ailand is common in the North and Northeast Northeast at 100 0- 1600 m elevation. P. kes 切 may occur mixed with montane hardwood trees trees or in relatively pure stands. It is relatively tolerant of frequent buming ， and thus has expanded its dominance in many montane habitats under human intervention. The biogeographical biogeographical and ecological pattems of distribution of this species in Th ailand have been been described in detail (WERNER ， 1993; SANTISUK ， 1997). Pinus Pinus merkusii Jungh. & De Vriese likewise has a spreading to rounded crown; needles occur occur with 2 in a fascicle ， and reach 150 ー250 mm in length. Th is pine occurs from East In dia across Southeast Asia to the Philippines to the east ， and south to Sumatra where it becomes the only pine species that naturally occurs south of the equator. In Th ailand it is a common species in the North ，Northeast and East where it occurs in dry deciduous dipteroca 叩 forests or lower montane forests at 60 0- 1300 m elevation (SANTISUK ， 1997). Rarely ，this species may occur together with the higher elevation P. kesiya. Podocarpus Podocarpus imbricatus B l. [=D αcη carpus imbricatus (B l.) De Laubenf.] is a large forest forest tree reaching 30 m in height and 120 cm in diamete r. Two forms of leaves 紅 e commonly present in this species ， with both occasionally found on the same individua l.