Leaf physiological versus morphological acclimation to high-light exposure at different stages of foliar development in oak

We investigated light acclimation in seedlings of the temperate oak Quercus petraea (Matt.) Liebl. and the co-occurring sub-Mediterranean oak Quercus pyrenaica Willd. Seedlings were raised in a greenhouse for 1 year in either 70 (HL) or 5.3% (LL) of ambient irradiance of full sunlight, and, in the following year, subsets of the LL-grown seedlings were transferred to HL either before leaf flushing (LL-HLBF plants) or after full leaf expansion (LL-HLAF plants). Gas exchange, chlorophyll a fluorescence, nitrogen fractions in photosynthetic components and leaf anatomy were examined in leaves of all seedlings 5 months after plants were moved from LL to HL. Differences between species in the acclimation of LL-grown plants to HL were minor. For LL-grown plants in HL, area-based photosynthetic capacity, maximum rate of carboxylation, maximum rate of electron transport and the effective photochemical quantum yield of photosystem II were comparable to those for plants grown solely in HL. A rapid change in nitrogen distribution among photosynthetic components was observed in LL-HLAF plants, which had the highest photosynthetic nitrogen-use efficiency. Increases in mesophyll thickness and dry mass per unit area governed leaf acclimation in LL-HLBF plants, which tended to have less nitrogen in photosynthetic components and a lower assimilation potential per unit of leaf mass or nitrogen than LL-HLAF plants. The data indicate that the phenological state of seedlings modified the acclimatory response of leaf attributes to increased irradiance. Morphological adaptation of leaves of LL-HLBF plants enhanced photosynthetic capacity per unit leaf area, but not per unit leaf dry mass, whereas substantial redistribution of nitrogen among photosynthetic components in leaves of LL-HLAF plants enhanced both mass- and area-based photosynthetic capacity.     

老鼠簕幼苗在潮汐环境下对不同光强的生理生态响应

采用自制潮汐模拟系统培养红树植物老鼠簕幼苗,设置7个相对于自然光5％、15％、20％、45％、60％、75％、100％的光照强度,研究了不同光强对老鼠簕幼苗从发芽至生长10个月的生理生态影响.随着光照强度的升高,幼苗的保存率、苗高、地径、根干质量、茎干质量、叶干质量、单株生物量、根冠比、根系活力、叶面积、叶绿素a、b含量均是先升后降;可溶性糖含量、净光合速率、蒸腾速率、气孔导度、最大净光合速率随光强增大而增加.在淹浸30 min内,不同光照强度的净光合速率均有增大的表现,而气孔导度均降低,且最终均稳定在初始值以下.试验表明:光照强度为45％时,多数生理生态指标表现为促进植物的生长;当光照强度为20％时,老鼠簕幼苗通过降低根冠比、光补偿点,增加苗高、叶绿素含量、叶面积和表观量子利用效率来提高自身光能获取的效率;当光照强度为5％时,光照会显著抑制幼苗的生长,但保存率依然在60％以上.可以认为,极低的光照强度致使幼苗生长缓慢,但并不影响其自然定居的密度;同时,在不同光强下,老鼠簕光饱和点和光补偿点均很低.以上可以解释淇澳岛红树林林下存在高密度老鼠簕的原因是由于其自身拥有高的耐阴能力,同时对光照减弱有极强的适应能力.     

光强对无瓣海桑幼苗的生长和光合特性的影响

根据实地测定人工无瓣海桑红树林不同环境下的光照强度,研究了不同光强环境对无瓣海桑幼苗的生长和光合特性的影响.结果表明:随着光照强度的降低,无瓣海桑幼苗的生长和光合特性指标水平均呈下降趋势,且不同光强处理间差异显著.在光照强度为全光照的80％和40％时,幼苗的各项生长指标下降,长势较全光照环境下的幼苗差;在荫蔽初期(2～4个月),弱光环境对幼苗的茎高、叶面积和叶片长宽比的增加有促进作用,随着荫蔽时间的延长,则产生抑制作用,不利于幼苗的生长;当光强达全光照的20％时,幼苗生长极为缓慢.在荫蔽处理180 d时,Sa80、Sa40、Sa20的幼苗死亡率分别为42％、70％、100％;在弱光环境下,无瓣海桑幼苗根、茎、叶的生物量分别下降了90％、80％、91％;随着环境光强水平的下降,无瓣海桑幼苗叶片的叶绿素含量、净光合速率等生理参数均呈下降趋势,各处理间差异显著.试验说明光强不足是造成无瓣海桑幼苗生长和光合水平低下及死亡率较高的主要原因,并对无瓣海桑幼苗的天然更新与自然扩散和人工造林技术进行了讨论.     

Effects of soil moisture and light intensity on ecophysiological characteristics of Amorpha fruticosa seedlings

We investigated the combined effects of soil moisture and light intensity on the growth, development and ecophysiological characteristics of one-year old Amorpha fruticosa seedlings. Soil moisture and light intensity influenced the ecophysiological characteristics of Amorpha fruticosa seedlings. Soil moisture resulted in the decreases of growth rate, individual size, net photosynthetic rate, transpiration rate, leaf water loss rate (WLR), and biomass accumulation of plant parts, and led to increased leaf water saturation deficit (WSD). Under water stress, more photosynthetic products were allocated to root growth. With decreasing light intensity, net photosynthetic rate, transpiration rate, chla/b, water saturation deficit, water use efficiency, water loss rate and biomass accumulation declined, while Chla, Chlb, Chla+b and carotenoids (Car) increased and more photosynthetic products were allocated to stem and leaf growth. Maximum growth vigor, net photosynthetic rate and total biomass accumulation in Amorpha fruticosa seedlings was recorded at 75 80% soil water-holding capacity and 100% light density in greenhouse environments.     

Increased photosynthesis following partial defoliation of field-grown Eucalyptus globulus seedlings is not caused by increased leaf nitrogen

Increased photosynthetic rates following partial defoliation may arise from changes in leaf biochemistry, water relations or nutrient status. Twelve-month-old field-grown Eucalyptus globulus Labill. seedlings were pruned from below to reduce the green crown depth by 50 (D50) or 70% (D70). Photosynthetic responses to light and CO2 concentration were examined before and one, three and five weeks after partial defoliation. One week after defoliation, photosynthetic rates were greater in seedlings in the D50 (21 micromol m(-2) s(-1)) and D70 (23 micromol m(-2) s(-1)) treatments than in control seedlings (15 micromol m(-2) s(-1)); however, there was little difference in photosynthetic rates between partially defoliated seedlings and control seedlings after 5 weeks. An analysis of the sensitivity of photosynthesis to biochemical parameters revealed that the transient increase in photosynthetic rate in response to partial defoliation was largely a function of the maximum rate of carboxylation (85-87%) and the maximum rate of RuBP regeneration (55-60%) rather than stomatal conductance (12-13%). Nitrogen increased in leaves following partial defoliation (increases of 0.6 and 1.2 g m(-2) for D50 and D70, respectively), but was accumulated in a non-photosynthetic form (i.e., there was no increase in nitrogen concentration of Rubisco or chlorophyll). Increased photosynthetic rates immediately following partial defoliation were primarily a result of increased activity rather than amount of photosynthetic machinery. There was no evidence that phosphorus was responsible for the increase in photosynthetic rates after partial defoliation.     

5种丛枝菌根真菌对君迁子幼苗光合生长的影响

为了探明丛枝菌根真菌对君迁子生长及光合作用的影响,以分别接种了细凹无梗囊酶(Acaulospora scrobiculata,简称AS)、聚丛根孢囊酶(Rhizophagus aggregatus,简称RA)、扭形多样孢囊酶(Diversispora trotuosa,简称DT)、根内根孢囊酶(Rhizophagus intraradices,简称RI)、摩西斗管囊酶(Funneliformis mosseae,简称FM)等5种丛枝菌根真菌和未接种菌根真菌的君迁子幼苗为试材,对6种处理下君迁子幼苗的生长情况和叶片的主要光合指标进行了观测,并用双曲线修正模型对所测数据进行拟合,得到光合响应曲线及各处理下君迁子幼苗各光合特征参数。结果表明:1菌根化的君迁子幼苗其株高、地径、叶片数、植株鲜质量等指标值均有明显的提高,与未接种的对照组相比,接种AS、RA、DT、RI、FM使君迁子的株高分别提高了48.22%、62.01%、14.34%、14.66%、29.01%;其地径分别提高了22.81%、46.84%、21.19%、17.23%、14.72%;其植株鲜质量分别提高了93.69%、103.93%、53.98%、68.52%、84.44%;其单株叶片数比对照组多2~5片。2菌根化的君迁子幼苗其净光合速率、光饱和点均高于对照组,而其光补偿点则反之。3各接种处理的净光合速率的日变化趋势较为一致,均呈"双峰"曲线,12:00~14:00时均存在"午休"现象,但接种处理下君迁子幼苗叶片的净光合速率、气孔导度、蒸腾速率、水分利用率的日均值均高于对照组。研究结果表明:接种丛枝菌根真菌能够显著提高君迁子幼苗的净光合速率,改善其对光的适应性,对植株的生长有显著的促进作用,但促进作用因菌种而异。     

Changes in photosynthesis and leaf characteristics with tree height in five dipterocarp species in a tropical rain forest

Variations in leaf photosynthetic, morphological and biochemical properties with increasing plant height from seedlings to emergent trees were investigated in five dipterocarp species in a Malaysian tropical rain forest. Canopy openness increased significantly with tree height. Photosynthetic properties, such as photosynthetic capacity at light saturation, light compensation point, maximum rate of carboxylation and maximum rate of photosynthetic electron transport, all increased significantly with tree height. Leaf morphological and biochemical traits, such as leaf mass per area, palisade layer thickness, nitrogen concentration per unit area, chlorophyll concentration per unit dry mass and chlorophyll to nitrogen ratio, also changed significantly with tree height. Leaf properties had simple and significant relationships with tree height, with few intra- and interspecies differences. Our results therefore suggest that the photosynthetic capacity of dipterocarp trees depends on tree height, and that the trees adapt to the light environment by adjusting their leaf morphological and biochemical properties. These results should aid in developing models that can accurately estimate carbon dioxide flux and biomass production in tropical rain forests.     

遮荫对珙桐幼苗光合特性及生长特征的影响研究

以不同遮荫条件(50%、25%和自然光)下适应生长1 a后的珙桐幼苗为研究对象,测定分析了珙桐幼苗的生理生化指标和生长的变化特征,结果表明:(1)不同的遮荫处理下,珙桐幼苗的净光合速率日变化曲线均为双峰型,有"午休"现象。但不同光强下出现峰值的大小和时间有差异。不同的光强下蒸腾速率日变化趋势也是不一致的,全天蒸腾速率大小顺序为一层遮荫(50%)两层遮荫(25%)全光照。(2)遮荫下珙桐的单叶面积、比叶面积和叶柄长均大于全光照下,表明珙桐利用弱光的能力很强,提高了对有限光资源的吸收。遮荫试验结果说明:适度的遮荫(50%透光率)有利于珙桐幼苗生长。     

Effect of shading on leaf structure and photosynthesis in young birches, Betula pendula Roth. and B. pubescens Ehrh.

The canopy structure and within-stand light conditions of several young birch (Betula pendula Roth. and B. pubescens Ehrh.) stands were studied. In addition, 2-year-old silver birch seedlings were subjected to varying degrees of artificial shading for one growing season in order to interpret the results of the former experiments. The shading increased the specific leaf area and the thickness of leaf mesophyll was reduced by increased shading. Similarly, the maximum photosynthetic rate and the light intensity for photosynthetic saturation were decreased in shading. Both phenomena seemed to be associated with the increase in specific leaf area and the decrease in the amount of chlorophyll per unit of leaf area.     

Photosynthesis, carbohydrate storage and survival of a native and an introduced tree species in relation to light and defoliation

Fraxinus uhdei (Wenz.) Lingelsh (tropical ash), a species introduced to Hawaii from Mexico, invades forests of the endemic tree Acacia koa A.Gray (koa). We examined physiological and morphological characteristics of koa and tropical ash to explore possible mechanisms that may facilitate invasion of koa forests by tropical ash. Seedlings of both species were grown in a greenhouse in three light treatments: 100% photosynthetic photon flux (PPF); 18% PPF; and 2% PPF inside the greenhouse. Light compensation point, maximum CO2 assimilation rate and dark respiration rate of seedlings differed significantly among light treatments, but were similar between species. A defoliation experiment indicated that tropical ash was better able to survive defoliation than koa, especially under high-light conditions. Tropical ash seedlings allocated more carbon (C) and nitrogen (N) to storage per unit PPF than koa seedlings. Total nonstructural carbohydrates were positively correlated with plant survival in both species. The patterns of C and N allocation associated with tropical ash seedlings favor their survival in high light, under intense herbivory and on sites where N availability is seasonal or highly variable. Variation in carbohydrate storage between koa and tropical ash greatly exceeded variation in photosynthetic performance at the leaf level.     

Photosynthetic light response of flooded cherrybark oak (Quercus pagoda) seedlings grown in two light regimes

Two-year-old cherrybark oak (Quercus pagoda Raf.) seedlings raised in full or partial (27%) sunlight were flooded for 30 days to study the effects of light availability and root inundation on photosynthetic light response. Compared with seedlings receiving full sunlight, seedlings receiving partial sunlight developed leaves with 90% greater blade area, 26% less mass per unit volume, and 35% lower nitrogen (N) concentration per unit area, leading to a 15% reduction in leaf photosynthetic capacity when carbon exchange rates were based on blade area. However, when carbon exchange rates were based on leaf mass, leaves acclimated to partial sunlight exhibited a 15% greater photosynthetic capacity realized primarily through an increased initial slope of the photosynthetic light response (A/PPFD) curve and increased net photosynthesis at leaf saturation (Amax). Short-term flooding increased leaf mass per unit area more than 19%, reduced foliar N concentrations per unit dry mass by 19%, and initiated reductions in Amax and apparent quantum yield (phi) of seedlings in both light regimes. Greatest impairment of Amax (56% area basis, 65% mass basis) and phi (40%) were observed in leaves receiving full sunlight, and the declines were concomitant with a 35% decrease in chlorophyll concentration. Flooding also depressed instantaneous photosynthetic N-use efficiency (PPNUE) such that Amax decreased 54%, and the initial slope of PPNUE/PPFD curves decreased 33 and 50% for leaves acclimated to partial and full sunlight, respectively. The A/PPFD patterns indicated that the magnitude of flood-induced inhibition of the photosynthetic mechanism of cherrybark oak seedlings is determined partly by the light environment.     

Photosynthetic capacity and nitrogen partitioning in foliage of the evergreen shrub Daphniphyllum humile along a natural light gradient

We examined the effects of leaf age and mutual shading on the morphology, photosynthetic properties and nitrogen (N) allocation of foliage of an evergreen understory shrub, Daphniphyllum humile Maxim, growing along a natural light gradient in a deciduous Fagus crenata-dominated forest in Japan. Seedlings in high-light environments were subject to greater mutual shading and 1-year-old foliage survival was lower than in seedlings in low-light environments, indicating that the survival rates of foliage were related to the degree of mutual shading. Although specific leaf area (SLA) in current- and 1-year-old foliage was curvilinearly related to daily photosynthetic photon flux (PPF), SLA was unaffected by leaf age, indicating that foliage in D. humile may not acclimate morphologically to annual changes in light caused by mutual shading. Light-saturated net photosynthetic rates (Pmax) were correlated with daily PPF in current-year foliage. In addition, a strong, positive relationship was found between nitrogen concentration per unit leaf area and Pmax. In contrast, the relationship among PPF, N and photosynthetic parameters in 1-year old foliage was weak because of the strong remobilization of N from older leaves to current-year foliage in plants growing in high light. However, the relationship between daily PPF and both photosynthetic N-use efficiency and the ratio of maximum electron transport rate to maximum carboxylation rate did not differ between current-year and 1-year-old foliage, suggesting that these responses help maintain a high photosynthetic efficiency even in older foliage. We conclude that D. humile maximizes whole-plant carbon gain by maintaining a balance among photosynthetic functions across wide ranges of leaf ages and light environments.     

Photosynthesis and carbon allocation of six boreal tree species grown in understory and open conditions

One-year-old seedlings of Abies balsamea (L.) Mill, Picea glauca (Moench) Voss, Pinus contorta Loudon, Betula papyrifera Marsh., Populus tremuloides Michx. and Populus balsamifera L. were transplanted in the spring, in pots, to the understory of a mixed P. tremuloides-P. balsamifera stand or to an adjacent open site. Growth and leaf characteristics were measured and photosynthetic light response curves determined in mid-August. Overall, the coniferous seedlings showed less photosynthetic plasticity in response to growth conditions than the deciduous species. Abies balsamea, P. glauca and B. papyrifera responded to the understory environment with higher leaf area ratios, and lower photosynthetic light saturation points and area-based leaf respiration relative to values for open-grown seedlings, while they matched or exceeded the height growth of open-grown seedlings. In contrast, seedlings of Pinus contorta, P. tremuloides and P. balsamifera displayed characteristics that were not conducive to survival in the understory. These characteristics included a high light saturation point and leaf dark respiration rate in P. contorta, and lower leaf area variables combined with higher carbon allocation to roots in P. tremuloides and P. balsamifera. By the second growing season, all seedlings of P. tremuloides and P. balsamifera growing in the understory had died.     

不同氮磷钾施肥配比对海芒果苗期生长的影响

不同氮磷钾配施对半年生海芒果盆苗生长影响的试验结果表明:促进苗高和地径生长的较优施肥配比为N0.7 g.盆-1、P2O50 g.盆-1、K2O 0.7 g.盆-1,苗高达到84.60 cm,比对照提高了58%,地径达到1.42 cm,比对照增加了5%;提高海芒果苗木根、茎、叶干质量及叶片叶绿素含量的较优施肥配比分别为N0.7 g.盆-1、P2O50.7g.盆-1、K2O 0 g.盆-1,其中根干质量较对照增加了66%,茎干质量较对照增加了124%,叶干质量较对照增加了103%,叶绿素含量最高达4.08 mg.g-1,比对照增加了86%;影响海芒果苗木净光合速率的较优施肥配比为N1.4g.盆-1、P2O50.35 g.盆-1、K2O0 g.盆-1,叶片净光合速率最高为10.81μmol.m-2.s-1,较同时刻对照处理的叶片净光合速率提高了2.44μmol.m-2.s-1。     

Leaf gas exchange characteristics of three neotropical mangrove species in response to varying hydroperiod

We determined how different hydroperiods affected leaf gas exchange characteristics of greenhouse-grown seedlings (2002) and saplings (2003) of the mangrove species Avicennia germinans (L.) Stearn., Laguncularia racemosa (L.) Gaertn. f., and Rhizophora mangle L. Hydroperiod treatments included no flooding (unflooded), intermittent flooding (intermittent), and permanent flooding (flooded). Plants in the intermittent treatment were measured under both flooded and drained states and compared separately. In the greenhouse study, plants of all species maintained different leaf areas in the contrasting hydroperiods during both years. Assimilation-light response curves indicated that the different hydroperiods had little effect on leaf gas exchange characteristics in either seedlings or saplings. However, short-term intermittent flooding for between 6 and 22 days caused a 20% reduction in maximum leaf-level carbon assimilation rate, a 51% lower light requirement to attain 50% of maximum assimilation, and a 38% higher demand from dark respiration. Although interspecific differences were evident for nearly all measured parameters in both years, there was little consistency in ranking of the interspecific responses. Species by hydroperiod interactions were significant only for sapling leaf area. In a field study, R. mangle saplings along the Shark River in the Everglades National Park either demonstrated no significant effect or slight enhancement of carbon assimilation and water-use efficiency while flooded. We obtained little evidence that contrasting hydroperiods affect leaf gas exchange characteristics of mangrove seedlings or saplings over long time intervals; however, intermittent flooding may cause short-term depressions in leaf gas exchange. The resilience of mangrove systems to flooding, as demonstrated in the permanently flooded treatments, will likely promote photosynthetic and morphological adjustment to slight hydroperiod shifts in many settings.     

Effects of potassium supply on limitations of photosynthesis by mesophyll diffusion conductance in Carya cathayensis

Potassium (K) influences the photosynthesis process in a number of ways; however, the mechanisms underlying the photosynthetic response to differences in K supply are not well understood. Concurrent measurements of gas exchange and chlorophyll fluorescence were made to investigate the effect of K nutrition on photosynthetic efficiency and mesophyll conductance (g(m)) in hickory seedlings (Carya cathayensis Sarg.) in a greenhouse. The results show that leaf K concentrations < 0.7-0.8% appeared to limit the leaf net CO2 assimilation rate (A), and that the relative limitation of photosynthesis due to g(m) and stomatal conductance (g(s)) decreased with increasing supplies of K. However, a sensitivity analysis indicated that A was most sensitive to the maximum carboxylation rate of Rubisco (V(c,max)) and the maximum rate of electron transport (J(max)). These results indicate that the photosynthetic rate is primarily limited by the biochemical processes of photosynthesis (V(c,max) and J(max)), rather than by g(m) and g(s) in K-deficient plants. Additionally, g(m) was closely correlated with g(s) and the leaf dry mass per unit area (M(A)) in hickory seedlings, which indicates that decreased g(m) and g(s) may be a consequence of leaf anatomical adaptation.     

遮阴处理对金蒲桃生长量及光合参数的影响

以2 a生金蒲桃(Xanthostemon chrysanthus)幼苗为材料,研究了全光照,50%遮阴,70%遮阴,90%遮阴4种遮阴处理对金蒲桃生长特性、生物量分配、光合生理变化的影响,结果表明:与自然光全处理对比,遮光极显著(P<0.01)地抑制了金蒲桃幼苗生物量的积累,遮光处理组叶片数量减少,叶生物量比下降,茎生物量比增加;光补偿点、光饱和点、暗呼吸速率和最大光合速率降低,光能利用效率低于全光照叶,强光下遮阴叶的净光合速率保持稳定.上述结果说明:遮阴处理后,金蒲桃在生长特性、生物量分配和光合参数上表现出对遮阴弱光的适应,表明金蒲桃是一种能广泛应用于各种光照条件的优良景观树种.     

不同光强下核桃楸、水曲柳和黄菠萝的光合生理特征

研究辽东山区次生林3种树种幼苗(核桃楸、水曲柳和黄菠萝)对生长光环境的适应性,在生长季测定4种光强下(全光、60%透光、30%透光、15%透光,分别记为FI,II,LJ和WI)树种幼苗叶片气体交换参数、净光合速率、单位叶面积叶绿素含量和比叶重(LMA).结果表明:随着光强的减弱,3个树种的光补偿点(LCP)、光饱和点(LSP)、最大光合速率(Pmax)、暗呼吸速率(Rd)、类胡萝卜素(Car)、LMA、单位叶鲜质量(LFA)均呈下降趋势;全光下单位叶面积的叶绿素Chl含量均低于弱光处理.本研究结果支持水曲柳在幼苗时期具有一定耐荫性的观点.树种生理生态指标的可塑性分析表明:黄菠萝能适应更宽的光强幅度,且黄菠萝的需光性大于核桃楸.不同光环境下3个树种的生理生态变化特征对解释森林生态系统内树种的共生和演替具有重要意义.     

南洋楹5个无性系苗木光合作用特性研究

采用Li-6400便携式光合作用测定仪,对南洋楹（Paraserianthes falcataria）A1、A8、B7、B8、D1共5个无性系苗木进行光合生理特征测定,探究其日净光合速率、日蒸腾速率特性及叶片位置与日平均净光合速率的关系。结果表明：南洋楹日净光合速率曲线与日蒸腾速率曲线在多云条件下均呈现单峰式,最高峰出现在10：00-12：00时;不同无性系苗木叶片位置对日平均净光合速率的影响不同,A1、A8、B7、B8无性系的上层叶片与中层叶片的日平均净光合速率显著高于下层叶片,而D1无性系苗木不同位置叶片的日平均净光合速率无显著差异。     

Relative importance of photosynthetic physiology and biomass allocation for tree seedling growth across a broad light gradient

Studies of tree seedling physiology and growth under field conditions provide information on the mechanisms underlying inter- and intraspecific differences in growth and survival at a critical period during forest regeneration. I compared photosynthetic physiology, growth and biomass allocation in seedlings of three shade-tolerant tree species, Virola koschynii Warb., Dipteryx panamensis (Pittier) Record & Mell and Brosimum alicastrum Swartz., growing across a light gradient created by a forest-pasture edge (0.5 to 67% diffuse transmittance (%T)). Most growth and physiological traits showed nonlinear responses to light availability, with the greatest changes occurring between 0.5 and 20 %T. Specific leaf area (SLA) and nitrogen per unit leaf mass (N mass) decreased, maximum assimilation per unit leaf area (A area) and area-based leaf N concentration (N area) increased, and maximum assimilation per unit leaf mass (A mass) did not change with increasing irradiance. Plastic responses in SLA were important determinants of leaf N and A area across the gradient. Species differed in magnitude and plasticity of growth; B. alicastrum had the lowest relative growth rates (RGR) and low plasticity. Its final biomass varied only 10-fold across the light gradient. In contrast, the final biomass of D. panamensis and V. koschynii varied by 100- and 50-fold, respectively, and both had higher RGR than B. alicastrum. As light availability increased, all species decreased biomass allocation to leaf tissue (mass and area) and showed a trade-off between allocation to leaf area at a given plant mass (LAR) and net gain in mass per unit leaf area (net assimilation rate, NAR). This trade-off largely reflected declines in SLA with increasing light. Finally, A area was correlated with NAR and both were major determinants of intraspecific variation in RGR. These data indicate the importance of plasticity in photosynthetic physiology and allocation for variation in tree seedling growth among habitats that vary in light availability.