The ratio of leaf to total photosynthetic area influences shade survival and plastic response to light of green-stemmed leguminous shrub seedlings

Different plant species and organs within a plant differ in their plastic response to light. These responses influence their performance and survival in relation to the light environment, which may range from full sunlight to deep shade. Plasticity, especially with regard to physiological features, is linked to a greater capacity to exploit high light and is usually low in shade-tolerant species. Among photosynthetic organs, green stems, which represent a large fraction of the total photosynthetic area of certain species, are hypothesized to be less capable of adjustment to light than leaves, because of biomechanical and hydraulic constraints. The response to light by leaves and stems of six species of leguminous, green-stemmed shrubs from dry and high-light environments was studied by growing seedlings in three light environments: deep shade, moderate shade and sun (3, 30 and 100 % of full sunlight, respectively). Survival in deep shade ranged from 2 % in Retama sphaerocarpa to 74 % in Ulex europaeus. Survival was maximal at moderate shade in all species, ranging from 80 to 98 %. The six species differed significantly in their ratio of leaf to total photosynthetic area, which influenced their light response. Survival in deep shade increased significantly with increasing ratio of leaf to total photosynthetic area, and decreased with increasing plasticity in net photosynthesis and dark respiration. Responses to light differed between stems and leaves within each species. Mean phenotypic plasticity for the variables leaf or stem specific mass, chlorophyll content, chlorophyll a/b ratio, and carotenoid to chlorophyll ratio of leaves, was inversely related to that of stems. Although mean plasticity of stems increased with the ratio of leaf to total photosynthetic area, the mean plasticity of leaves decreased. Shrubs with green stems and a low ratio of leaf to total photosynthetic area are expected to be restricted to well-lit habitats, at least during the seedling stage, owing to their inefficient light capture and the low plasticity of their stems.     

Growth and photosynthetic responses of the federally endangered shrub, Lindera melissifolia (Lauraceae), to varied light environments

Photosynthetic, morphological, and growth responses to light environment can be useful measurements to determine favorable habitat conditions for the conservation of endangered species. For Lindera melissifolia (Walt.) Blume, we compared morphological and photosynthetic responses under natural and controlled light regimes, and growth under three light treatments: 100%, 42%, and 19% full sunlight. Typical sun-shade morphological responses to decreasing light levels included decreased stomatal density, increased specific leaf area, and increased leaf area ratio. Photosynthetic capacity (3-6 μmol CO(2) · m(-2) · s(-1)) was consistent with other shade-tolerant species. Light-saturated rates of photosynthesis of experimental plants increased with increasing light up to 42% sunlight, but declined at 100% sunlight. The 100% light treatment also resulted in lower plant biomass, primarily from a reduction in root biomass. Results indicate that canopy conditions at levels below 40% sunlight are optimal for plant growth and should be considered in management and reintroduction efforts for this species.     

Plastic responses of 4 tree species of successional subalpine coniferous forest serals to different light regimes

The morphological and physiological plasticity to 6 light conditions was investigated for seedlings of 4 tree species dominating at different successional serals in subalpine coniferous forests in eastern Qinghai-Tibet Plateau, China. Abies faxoniana is a late successional species, while Betula albo-sinensis is a pioneer tree species, with Picea asperata and Acer davidii among other mid-late successional species. To compare the responses of photosynthetic characters to different growth light conditions, the seedlings were potted and placed in artificially shaded chambers with gradients of 100%, 55%, 40%, 25%, 15% and 7% of the full sunlight, respectively. During two and a half years' cultivation, various morphological and photosynthetic parameters were measured and analyzed. The results were: 1) all seedlings of the four species under the low growth light conditions showed decrease in root collar diameter, relative growth rate, leaf thickness, root mass ratio, leaf area-based photosynthetic capacity, dark respiration rate, light saturation point and light compensation point, while showed increase in specific leaf area, above-ground to under-ground mass ratio, specific stem length, leaf mass ratio and stem mass ratio; 2) under most light conditions, A. faxoniana of the two conifers revealed lower values in both leaf area-based photosynthetic capacity and respiration rates than P. asperata; the same fact held true for the two broad-leaved trees with lower values observed in B. albo-sinensis; 3) under higher light conditions, relative growth rates of P. asperata and B. albo-sinensis got higher values than those of A. faxoniana and A. davidii, while contrary results were obtained under lower light regimes; 4) the means of phenotypic plastic indices of the eleven morphological and physiological parameters of P. asperata and B. albo-sinensis were higher than those of A. faxoniana and A. davidii, respectively. The findings indicate that A. faxoniana has better adaptation to low light regimes, but as a shade-tolerant species, it is not so adapted to low light regimes as the trees of earlier successional serals, especially P. asperata and B. albo-sinensis. Of the four tree species, physiological plastic indices were higher than morphological plastic indices, suggesting that morphological plasticity plays an important role in their adaptation to different growth light conditions. The results also support the hypothesis that ecophysiological traits of tree species determine their successional status and associate habitats of their seedlings.     

Morphological and Physiological Acclimation Responses to Contrasting Light and Water Regimes in <Emphasis Type="Italic">Primula sieboldii</Emphasis>

The effects of the availability of light (high, medium and low) and soil water (wet and dry) on morphological and physiological traits responsible for whole plant carbon gain and ramet biomass accumulation were examined in a splitter-type clonal herbaceous species Primula sieboldii, a spring plant inhabiting broad range of light environments including open grassland and oak forest understory. Growth experiments were conducted for three genets originated from natural microhabitats differing in light and soil water availability. Ramets of a genet from high light and wet microhabitat, which were grown in low light (relative photon flux density: R-PPFD of 5%) showed 41% less light-saturated photosynthetic rate, 50% less dark respiration rate and earlier defoliation than the ramets in high light (R-PPFD of 61%). The estimation of daily photosynthesis revealed that the light acclimation response in leaf gas exchange contributes to efficient carbon gain of whole plants, irrespective of experimental light conditions. Water stress increased root weight ratio, decreased ramet leaf area, petiole length and photosynthetic capacity. These morphological effects of water stress were larger in high and medium light regimes than in low light regime. The consequence of the above responses was recognized in the relative growth rate of the ramets. The relative growth rate of the ramets in high light with wet regime was four-fold of that in low light plus wet regime, and was 1.5-fold of that in high light plus dry regime. However, even in low light and/or dry regimes, ramets kept positive relative growth rates and produced gemma successfully. We could not detect significant variation in growth responses among genets. The high photosynthetic plasticity revealed in the present study should enable Primula sieboldii to inhabit in a broad range of light and soil water availability.     

不同光环境对桤木幼苗生长和光合特性的影响

通过设置3个光照强度(100%、56.2% 和12.5%),模拟森林幼苗生长的旷地(采伐迹地)、林窗和林下光环境,研究不同光照强度对外来种台湾桤木和乡土种四川桤木幼苗的生长、光合特性以及生物量积累与分配的影响.结果表明： 低光环境限制了两种桤木幼苗形态指标的增长,适当遮荫的林窗环境比旷地更有利于幼苗的生长.台湾桤木幼苗具有较高的比叶面积和相对生长速率,较大的单叶面积、叶长、叶宽、株高和基径,较少的叶片数和较低的叶面积比、叶柄长.低光环境下,台湾桤木幼苗的最大净光合速率、光饱和点和表观光量子效率较高,光补偿点和暗呼吸速率较低.随着光照强度的降低,台湾桤木幼苗具有更高的根生物量比和更低的叶生物量比;四川桤木幼苗则相反,加剧了动物取食和机械损伤的风险.     

四种亚高山针叶林树种的表型可塑性对不同光照强度的响应

以青藏高原东缘亚高山针叶林群落演替后期种岷江冷杉、演替中后期种粗枝云杉和青榨槭、及先锋树种红桦为材料,研究了不同光强下生长的4种树苗生长、生物量分配、叶片形态和光合特性,探讨植物幼苗的形态和生理特征的表型可塑性与光适应的关系。结果表明：（1）弱光环境中生长的4种植物的基茎、相对生长速率、叶片厚度、根重比、最大净光合速率、光饱和点、光补偿点、暗呼吸速率较低,而比叶面积、地上／地下生物量、茎长／茎重、叶重比和茎重比较高。（2）大部分光环境下岷江冷杉幼苗的最大净光合速率和暗呼吸速率低于粗枝云杉,青榨槭幼苗的最大净光合速率和暗呼吸速率略低于红桦。（3）高光强下生长的粗枝云杉和红桦幼苗的相对生长速率分别大于岷江冷杉和青榨槭,但在低光强下则与之相反。（4）粗枝云杉和红桦幼苗的11种可塑性指数平均值则分别大于岷江冷杉和青榨槭。岷江冷杉适应弱光环境的能力略强于粗枝云杉和红桦,但适应强光的能力较差。生理适应的可塑性指数大于形态适应的可塑性指数,表明前者在4种植物幼苗光适应方面起到了重要的作用。研究结果支持树种的生理生态特性决定了其演替状况和生境选择的假说。     

Effects of light and soil water availability on leaf photosynthesis and growth of Arisaema heterophyllum,a riparian forest understorey plant

The effects of soil-water availability on leaf light acclimation and whole-plant carbon gain were examined in Arisaema heterophyllum Blume, a riparian deciduous forest understorey plant. Photosynthesis, above-ground morphology and ramet biomass accumulation (relative growth rate: RGR of a corm for a full leaf life-span) were measured on plants raised under three light treatments combined with two soil water conditions. The two higher light treatments during growth (high: max. 550 μmol photons m^–2 s^–1; medium: 150 μmol photons m^–2 s^–1) resulted in a twofold increase in RGRs, 30% higher photosynthetic capacities and 20% less photosynthetic low-light use efficiency than those under a low light condition (50 μmol photons m^–2 s^–1). Leaf area was the smallest and leaf mass area ratio was the largest under the high light treatment. Water stress decreased both photosynthetic rate and leaf area and, hence, RGR in all the light regimes. However, water stress did not alter the general patterns of physiological and morphological responses to different light regimes. We estimated that higher photosynthetic low-light use efficiency and larger leaf area in the low light leaf would lead to a threefold carbon gain as compared with the high light leaf under simulated low light conditions. Both experimental and simulation results suggest that the physiological and morphological acclimations tend to be beneficial to carbon gain when light availability is low, whereas they favor increased water use efficiency when light availability is sufficiently high. Electronic Publication     

Photosynthetic responses of <Emphasis Type="Italic">Chrysanthemum morifolium</Emphasis> to growth irradiance: morphology,anatomy and chloroplast ultrastructure

Seedlings of Chrysanthemum, cultivar ‘Puma Sunny’, were grown under a range of shading regimes (natural full sunlight, 55, 25, and 15% of full sunlight) for 18 days. Here, we characterized effects of varying light regimes on plant morphology, photosynthesis, chlorophyll fluorescence, anatomical traits, and chloroplast ultrastructure. We showed that leaf color was yellowish-green under full sunlight. Leaf area, internode length, and petiole length of plants were the largest under 15% irradiance. Net photosynthetic rate, water-use efficiency, PSII quantum efficiency, and starch grain were reduced with decreasing irradiance from 100 to 15%. Heavy shading resulted in the partial closure of PSII reaction centers and the CO₂ assimilation was restricted. The results showed the leaves of plants were thinner under 25 and 15% irradiance with loose palisade tissue and irregularly arranged spongy mesophyll cells, while the plants grown under full sunlight showed the most compact leaf palisade parenchyma. Irradiance lesser than 25% of full sunlight reduced carbon assimilation and led to limited plant growth. Approximately 55% irradiance was suggested to be the optimal for Chrysanthemum morifolium.     

闽楠幼树光合特性及生物量分配对光环境的响应

设置100%光环境(L100)、40%光环境(L40)、8%光环境(L8)3种光照梯度,分析万木林闽楠(Phoebe bournei)幼树的光合特性及生物量分配特征对不同光环境的响应。结果表明:(1)闽楠幼树在不同光环境下的最大净光合速率(Pnmax),表观量子效率(AQY),光饱和点(LSP),光补偿点(LCP),暗呼吸速率(Rd)均有显著差异(P<0.05),且随着光照强度的降低,Pnmax,LSP,LCP,Rd随之降低,而AQY却呈现升高的趋势。(2)总生物量、茎生物量、叶生物量、根生物量均表现为L100最大,根冠比、叶生物量比、茎生物量比及根生物量比在3种光环境下无显著差异。(3)闽楠幼树通过改变光合特性,生物量积累来适应光环境的变化,其中光照强度的降低限制了生物量的积累,但并未显著改变生物量地上地下分配比例。闽楠幼树在3种光环境下生物量分配比例并无显著的改变,生物量分配可塑性极低可能是闽楠零散分布的一个重要非人为干扰因素。(4)闽楠幼树所采取的生存策略以地上部分生长为主,光照强度降低时则采取保守策略进行缓慢的资源获取和消耗,全光照条件下采取快速的资源获取和消耗策略。未来造林时可以将闽楠与毛竹(Phyllostachys pubescens)混交来减少郁闭度,促进闽楠幼树的生长。     

Influence of light intensity during growth on photosynthesis and activity of several key photosynthetic enzymes in a C4 plant (Zea mays)

Maize ( Zea mays L. Hybrid Sweet Corn, Royal Crest), a C₄ plant, was grown under different light regimes, after which the rate of photosynthesis and activities of several photosynthetic enzymes (per unit leaf chlorophyll) were measured at different light intensities. Plants were grown outdoors under direct sunlight or 23% of direct sunlight, and in growth chambers at photosynthetic photon flux densities of about 20% and 8% of direct sunlight. The plants grown under direct sunlight had a higher light compensation point than plants grown under lower light. At a light intensity about 25% of direct sunlight, plants from all growth regimes had a similar rate of photosynthesis. Under saturating levels of light the plants grown under direct sunlight had a substantially higher rate of photosynthesis than plants grown under the lower light regimes. The higher photosynthetic capacity in the plants grown under direct sunlight was accompanied by an increased activity of several photosynthetic enzymes and in the amount of the soluble protein in the leaf. Among five photosynthetic enzymes examined, RuBP carboxylase (EC 4.1.1.39) and pyruvate, Pi dikinase (EC 2.7.9.1) were generally just sufficient to account for rates of photosynthesis under saturating light; thus, these may be rate limiting enzymes in C₄ photosynthesis. Pyruvate, Pi dikinase and NADP-malate dehydrogenase (EC 1.1.1.82) were the only enzymes examined which were light activated and increased in activity with increasing light intensity. In the low light grown plants the activity of pyruvate, Pi dikinase closely paralleled the photosynthetic rate measured under different light levels. With the plants grown under direct sunlight, as light intensity was increased the activation of pyruvate, Pi dikinase and NADP⁺-malate dehydrogenase proceeded more rapidly than photosynthesis.     

Adaptive radiation of photosynthetic physiology in the Hawaiian lobeliads: light regimes, static light responses, and whole-plant compensation points

Six endemic genera/sections of lobeliads (Campanulaceae) occupy nearly the full range of light regimes on moist sites in the Hawaiian Islands, from open alpine bogs and seacliffs to densely shaded rainforest interiors. To determine whether this clade has undergone a corresponding adaptive radiation in photosynthetic adaptations, we studied the natural light habitats and physiological characteristics of 11 species representing each sublineage. Across species in the field, average photon flux density (PFD) varies from 2.3 to 30.0 mol · m(-2) · d(-1), and maximum assimilation rate (A(max)) ranges from 0.17 to 0.35 μmol CO(2) · g(-1) · s(-1). Across species, A(max), dark respiration rate (R), Michaelis-Menten constant (k), light compensation point, specific leaf area (SLA), maximum carboxylation rate (V(cmax)), maximum rate of electron transport (J(max)), photosynthesis at saturating CO(2) (A(satCO(2))), and carboxylation efficiency (α) all increase significantly and in tightly coupled fashion with PFD, in accord with classical economic theory. Area-based rates have a higher degree of physiological integration with each other and tighter coupling to PFD than the corresponding mass-based rates, despite the energetic importance of the latter. Area-based rates frequently show adaptive cross-over: high-light species outperform low-light species at high PFD and vice versa at low PFD. A(max)-mass has little relationship to leaf mass per unit area (LMA), leaf N content, or leaf lifespan individually, but a multiple regression explains 96% of the variance in A(max)-mass across species in terms of SLA, leaf N content, and average PFD. Instantaneous leaf compensation points range from 0.1 to 1.2% full sunlight, far lower than the ecological (whole-plant) compensation points (ECPs) of 1.1 to 29.0% sunlight calculated based on photosynthetic parameters, leaf longevity, and allocation to leaf vs. nonleaf tissue. The ECPs are much closer to the lower limits of PFD actually experienced by lobeliads, suggesting they may play an important role in restricting species distributions. Taken together, these data provide evidence for an adaptive radiation in photosynthetic traits that is strongly correlated with-and indeed may help determine-the light regime that each species inhabits.     

光照对鄂东南2种落叶阔叶树种幼苗生长、光合特性和生物量分配的影响

通过设置4个光照梯度(25%、12%、6%和3%自然光)模拟鄂东南低山丘陵地区落叶阔叶林林下的光环境,研究了2种耐荫性不同的树种幼苗--麻栎(Quercus acutissima)和化香(Platycarya strobilacea)不同光强下的存活率、光合特性、生长和生物量分配,探讨了低光环境中耐荫性不同的树种幼苗维持自身碳平衡的机制和权衡"存活-生长"选择的生活史策略。结果表明:(1)低光下的2个树种幼苗的生长、光合特性和生物量分配具有显著性差异。(2)各个光照梯度下麻栎幼苗都生长良好,存活率保持在35%以上,而化香幼苗遭遇高的死亡率,80d后3%和6%自然光下的幼苗全部死亡;低光环境中麻栎幼苗比化香幼苗具有更大的表观光量子(AQY)和最大净光合效率(Pmax),更低的光补偿点(LCP)和暗呼吸效率(Rd),即耐荫性较强的麻栎幼苗比耐荫性较弱的化香幼苗具有更高的低光碳同化率和碳捕获能力。(3)2个树种幼苗的成活率与RGR呈负相关关系,各个光照梯度下耐荫性较弱的化香幼苗的相对生长率(RGR)显著高于耐荫性较强的麻栎幼苗,而两个树种幼苗的净同化率(NAR)无明显差异。相对于麻栎幼苗较高的根生物量比(RMR),化香幼苗将更多的生物量分配给叶部,因而具有较高的叶生物量比(LMR)、叶面积比(LAR)和比叶面积(SLA)。不同耐荫性的幼苗生长及生物量分配方式的差异是植物"存活-生长"权衡后的结果,耐荫性弱的化香幼苗具有较高的生长潜力和较弱的自我保护能力,而耐荫性强的麻栎幼苗具有更高的低光碳储量,能够维持更好的低光碳平衡,具有竞争优势。     

四种热带雨林树种幼苗比叶重,光合特性和暗呼吸对生长光环境的适应

雾凉季研究了西双版纳热带雨林4种植物幼苗对生长光环境的适应,其中两个树种幼苗喜光（团花和滇南插柚紫）,两个树种幼苗耐荫（滇南红厚壳和玉蕊）发现弱光环境中生长的4种植物比叶重、光合能力、光饱和点、光补偿点暗呼吸速度、叶绿素a/b比较低,叶绿素含量较高。玉蕊和滇南红厚壳幼苗的光合能力和呼吸速度 于团花树和滇南插柚紫。团花树和滇南插机紫的比叶重和光合作用的可塑性大于玉蕊和滇南红厚壳。高光强下生长的团花树和滇南插机紫增加叶氮分配给羧化酶的比较。减少分配给叶绿素的比例。滇南红厚壳和玉蕊适应弱光环境的能力略强于团花树和滇南插机紫,但适应强光的能力较差。研究结果支持树种的生理生态特性决定了其演替状况和生境选择的假说,单位干重叶的光合能力和呼吸速率并未表现出利于光适应的可塑性,表明4种植物生理适应能力较差,形态学上的适应在4种热带雨林树种幼苗光适应方面起到了重要的作用,叶氮分配也是它们光适应的策略之一。     

Photosynthetic acclimation of Tradescantia albiflora to growth irradiance: morphological, ultrastructural and growth responses

Tradescantia albiflora (Kunth), a trailing ground species naturally occurring in deep shade in rainforests, has an unusual photosynthetic acclimation profile for growth irradiance. Although capable of increasing its capacity for electron transport, photophosphorylation and carbon fixation when grown in full sunlight, Tradescantia has constant chlorophyll alb ratios, photosystem reaction centre stoichiometry and pigment-protein composition at all growth irradiances (Chow et al. 1991. Physiol. Plant. 81: 175–182). To gain an insight into the compensatory strategies which allow Tradescantia to grow in both high and low lights, plants were grown under shade cloth (100 to 1.4% relative growth irradiance) and leaf and chloroplast attributes were compared. While shade Tradescantia chloroplasts had three times more chlorophyll per chloroplast and twice the length of thylakoid membranes compared to plants grown in full sunlight, the ratios of appressed to nonappressed thylakoid membranes were constant. The average net surface charge density of destacked thylakoids was the same for plants grown at moderate and low-irradiance, consistent with their similar stacking profiles. Tradescantia plants grown in direct sunlight had 10-times more fresh and dry weight per plant compared to plants grown in shade, despite a lower photosynthetic capacity on a leaf area basis with partial photoinhibition. We conclude that having a light-harvesting apparatus permanently locked into the "shade-plant mode " does not necessarily prevent a plant from thriving in high light. Analyses of leaf growth at different irradiances provide a partial explanation of the manner in which Tradescantia compensates for very low photosynthetic capacity per unit leaf in sunlight.     

Does shading explain variation in morphophysiological traits of tropical epiphytic orchids grown in artificial conditions?

Light is one of the main factors of physical environment and it controls plant growth and development by interfering with photosynthesis, especially concerning CO₂ assimilation. Photosynthetic characteristics and growth of C3 epiphytic orchids Miltonia flavescens and Miltonia spectabilis var. moreliana were analyzed under four radiation regimens (25, 50 and 75?% of global radiation and full sunlight). Anatomical characterizations were performed on plants grown at 25?% shade. Artificial shading was obtained using different shading nylon nets. The highest values of light-saturated photosynthetic, dark respiration, net photosynthetic and leaf transpiration rates, stomatal conductance and intercellular to atmospheric CO₂ concentration ratio were observed at full sunlight and 25?% shade. Moreover, both species allocated greater amount of leaf dry weight in those treatments. On the other hand, it was observed a greater investment in pseudobulb biomass in more shaded conditions (50 and 75?%), corroborating with the highest values of intrinsic water-use efficiency observed in those treatments. It was found a significant effect of shading on leaf area and specific leaf area. The anatomical features reflected strategies to save water. The phenotypic plasticity and principal component analysis suggested that the physiological traits were more responsive to light levels than the morphological traits. The results indicate that those species appear to be adapted to high irradiances conditions and are capable of adjusting, via morphophysiological changes, to light availability.     

The influence of light on the growth of watercress (<Emphasis Type="Italic">Nasturtium officinale</Emphasis> R. Br.)

In stream ecosystems, the growth of aquatic primary producers is affected by spatial and temporal variations in the riparian canopy, which can influence the availability of light resources. Aquatic plants can acclimate to low light environments by employing a suite of morphological or physiological mechanisms to increase light capture or photosynthetic efficiency. Some species may also use alternate types of propagules to colonize environments with heterogeneous light environments. In a greenhouse experiment we examined the morphological and physiological response of watercress (Nasturtium officinale R. Br.) to a gradient of increasing light levels, which ranged from 7% ambient light to full sunlight. We also determined if watercress seedlings and vegetative fragments differed in their growth response to increasing light levels. Total biomass and root biomass of seedlings and vegetative fragments decreased with decreasing light levels. The difference in plant biomass across treatments was due to morphological changes in total canopy area and leaf area, both of which increased with decreasing light levels. Seedlings and vegetative fragments did not differ in their response to light availability, but vegetative fragments had higher final biomass as a result of higher initial biomass. Physiological acclimation to low light levels appears to be of secondary importance for watercress as the concentrations of total chlorophyll, chlorophyll a, chlorophyll b, and chlorophyll a:b did not differ among light levels or between seedlings and vegetative fragments. Seedlings and vegetative fragments grown under high light levels had a greater percentage of carbon and a lower percentage of nitrogen than plants grown under low light conditions. The results of this study indicate that watercress displays considerable morphological plasticity and acclimates to low light conditions primarily by increasing leaf area and canopy surface area. There is no evidence that the type of watercress propagule (seedling vs. vegetative fragment) imparts any growth advantage in low light environments and watercress grown from either type of propagule showed no differences in their morphological or physiological responses to varying light regimes. Handling editor: S. M. Thomaz     

南京地区落叶栎林主要木本植物的展叶动态研究

 植物的展叶过程是由自身遗传因子决定的,同时又受到多种生态因子的调节,反映了植物的生活史对策和群落物种多样性的维持机制。在2001和2002年的3～6月间,不定期记录了南京地区三个落叶栎(Quercus spp.)林中主要木本植物的展叶情况,包括被标记标准枝的叶数、叶的长度、宽度、叶面积、叶干重等参数。结果表明在所调查的落叶栎林中,林冠层物种的成熟叶面积和单位叶面积干重都显著大于林下层物种;最早展叶的物种为林下层物种,但林冠层展叶顺序与林下层无显著差异。叶面积越大、单位叶面积干重越小的物种展叶越晚;林冠层物种展叶较林下层快,物种成熟叶面积越大,展叶速率越大。最后对展叶顺序和展叶速度的生态学意义作了讨论。     

Functional correlates of leaf demographic response to gap release in saplings of a shade-tolerant tree,<Emphasis Type="Italic"> Elateriospermum tapos</Emphasis>

For a shade-tolerant SE Asian tropical tree, Elateriospermum tapos (Euphorbiaceae), we studied field-established saplings in gaps and the shaded understory to test the hypothesis that differences in leaf demography and leaf life span under contrasting light regimes should be functionally correlated with architecture, self-shading and nitrogen distribution within the sapling crown. Rates of leaf production and net leaf gain were greater for saplings in gaps than those in the understory. Median leaf life span was approximately 26 months in the gap saplings, while it was estimated to be greater than 38 months in the understory saplings. Consequently, gap saplings had a greater standing leaf number and experienced greater degrees of self-shading than understory saplings. Light availability at individual leaves, estimated by a combination of canopy photos and a three-dimensional architecture model, were negatively correlated with leaf age in gap saplings but not so in understory saplings. Leaf nitrogen content per unit area (N_area) was influenced more by light availability than by leaf age in the gap saplings. In contrast, in understory saplings, N_area was neither correlated with light availability nor with leaf age, and did not decrease significantly before 38 months in leaf age. We conclude that saplings of this shade-tolerant species apparently prolong their leaf life span in the shaded understory through slower rates of leaf production, lower standing number of leaves and lower degrees of self shading than in gap, and that the rate of decline of N_area with leaf age depends on architecture and self-shading regimes that respond to changes in light regimes.     

Plasticity in seedling morphology,biomass allocation and physiology among ten temperate tree species in response to shade is related to shade tolerance and not leaf habit

• Mechanisms of shade tolerance in tree seedlings, and thus growth in shade, may differ by leaf habit and vary with ontogeny following seed germination. To examine early responses of seedlings to shade in relation to morphological, physiological and biomass allocation traits, we compared seedlings of 10 temperate species, varying in their leaf habit (broadleaved versus needle‐leaved) and observed tolerance to shade, when growing in two contrasting light treatments – open (about 20% of full sunlight) and shade (about 5% of full sunlight).
• We analyzed biomass allocation and its response to shade using allometric relationships. We also measured leaf gas exchange rates and leaf N in the two light treatments.
• Compared to the open treatment, shading significantly increased traits typically associated with high relative growth rate (RGR) – leaf area ratio (LAR), specific leaf area (SLA), and allocation of biomass into leaves, and reduced seedling mass and allocation to roots, and net assimilation rate (NAR). Interestingly, RGR was not affected by light treatment, likely because of morphological and physiological adjustments in shaded plants that offset reductions of in situ net assimilation of carbon in shade. Leaf area‐based rates of light‐saturated leaf gas exchange differed among species groups, but not between light treatments, as leaf N concentration increased in concert with increased SLA in shade.
• We found little evidence to support the hypothesis of a increased plasticity of broadleaved species compared to needle‐leaved conifers in response to shade. However, an expectation of higher plasticity in shade‐intolerant species than in shade‐tolerant ones, and in leaf and plant morphology than in biomass allocation was supported across species of contrasting leaf habit.

     

Seedling growth strategies in Bauhinia species: comparing lianas and trees

BACKGROUND AND AIMS: Lianas are expected to differ from trees in their growth strategies. As a result these two groups of woody species will have different spatial distributions: lianas are more common in high light environments. This study determines the differences in growth patterns, biomass allocation and leaf traits in five closely related liana and tree species of the genus Bauhinia. METHODS: Seedlings of two light-demanding lianas (Bauhinia tenuiflora and B. claviflora), one shade-tolerant liana (B. aurea), and two light-demanding trees (B. purpurea and B. monandra) were grown in a shadehouse at 25% of full sunlight. A range of physiological, morphological and biomass parameters at the leaf and whole plant level were compared among these five species. KEY RESULTS: The two light-demanding liana species had higher relative growth rate (RGR), allocated more biomass to leaf production [higher leaf mass fraction (LMF) and higher leaf area ratio (LAR)] and stem mass fraction (SMF), and less biomass to the roots [root mass fraction (RMF)] than the two tree species. The shade-tolerant liana had the lowest RGR of all five species, and had a higher RMF, lower SMF and similar LMF than the two light-demanding liana species. The two light-demanding lianas had lower photosynthetic rates per unit area (A(area)) and similar photosynthetic rates per unit mass (A(mass)) than the trees. Across species, RGR was positively related to SLA, but not to LAR and A(area). CONCLUSIONS: It is concluded that the faster growth of light-demanding lianas compared with light-demanding trees is based on morphological parameters (SLA, LMF and LAR), and cannot be attributed to higher photosynthetic rates at the leaf level. The shade-tolerant liana exhibited a slow-growth strategy, compared with the light-demanding species.