森林光环境对4种乔木幼树光合和光谱反射特性的影响

在林窗、林缘、林下3种自然光环境下,对吉林蛟河阔叶红松林常见树种拧筋槭、白牛槭、色木槭和红松的光合和光谱特性进行对比研究,以期从生理生态角度探讨它们对自然光环境的适应能力和响应机制。结果表明：4种乔木幼树叶片的光饱和点(LSP)和光补偿点(LCP)随着生长环境光强的下降而减小,林下各树种幼树LSP和LCP显著低于林窗内幼树(P<0.05);除白牛槭外林下其他树种最大净光合效率(P_nmax)均显著小于林窗内幼树(P<0.05);不同树种幼树表观量子效率(AQY)和暗呼吸速率(R_d)随光环境的变化并没有出现明显的变化规律,各环境间差异较小。除白牛槭外,其他树种幼树叶绿素归一化指数(Chl NDI)随环境光强的减少而增大,林下树种的光化学反射指数(PRI)普遍高于光条件更好环境下树种,说明林下幼树叶片叶绿素含量和光合速率大于其他光环境;各树种植物叶片水分指数(WI)在不同光环境之间存在显著差异,环境光强越大植物叶片WI越小,植物叶片水分浓度越小。林缘下3种槭属幼树结构不敏感植被光谱指数(SIPI)显著小于其他光环境(P<0.05)...     

亚热带10种蕨类植物光响应模型拟合及光合特性研究

通过合适的光响应模型来准确计算植物光合参数是研究植物光合特性的重要手段。为深入了解亚热带蕨类植物的光合特性,采用直角双曲线模型、非直角双曲线模型、指数模型和直角双曲线修正模型等4种常用光响应模型分别对10种亚热带蕨类植物进行光响应曲线拟合。通过分析决定系数(R~2)、均方根误差(RMSE)、平均绝对误差(MAE)、光饱和点(LSP)、光补偿点(LCP)、最大净光合速率(P_nmax)、暗呼吸速率(R_d)和表观量子效率(AQE)等9种参数,探讨亚热带蕨类植物的光响应模型拟合效果及其光合特性。结果表明：直角双曲线修正模型和非直角双曲线模型对本研究10种亚热带蕨类植物的拟合效果较好,其中直角双曲线修正模型的LSP拟合效果最好,非直角双曲线模型的拟合精度最高。光合参数的聚类分析和TOPSIS(Technique for Order Preference by Similarity to an Ideal Solution)综合评价法表明,10种亚热带蕨类植物的光合特性既具有相似性又存在物种特异性。黑鳞耳蕨(Polystichum makinoi(Tag...     

Chlorophyll Fluorescence and Photosynthetic Gas Exchange Responses to Irradiance of Tree of Heaven (Ailanthus Altissima) in Contrasting Urban Environments

Sun-and shade-adapted plants of Ailanthus altissima utilized thermal-dissipative photoprotection (NPQ) across a range of photosynthetic photon flux densities (PPFD), with higher NPQ and lower maximum quantum yield of photosystem 2 photochemistry (F_v/F_m) in sun-adapted individuals, suggesting increased engagement of antennae-based quenching. Photosynthetic quantum requirements (Q_req; number of photons per CO₂) were similar in sun and shade plants, but were low and comparable to forest understory species. Diurnal measurements showed that PPFDs in both habitats were consistently above photosynthetic compensation irradiance, and frequently exceeded saturating values. In addition, sun- and shade-adapted individuals possessed stomata that tracked short-term fluctuations in PPFD. Thus A. altissima may be unique in that it couples high, shade-plant like photosynthetic efficiency with high photosynthetic capacity in high-irradiance, while stomatal attributes that optimize water use efficiency are maintained in the shade. These features may contribute to success of A. altissima in establishing in disturbance-prone urban systems, and facilitate its spread into more PPFD-limited and competitive natural ecosystems.     

水盐梯度下克里雅河流域芦苇光合响应特征

选择新疆克里雅河流域地下水埋深不同的样点芦苇为材料,采用Li-6400便携式光合系统仪对各样点芦苇的光合响应特征进行实地测定,探讨其适应干旱胁迫和盐胁迫环境的光合机理。结果显示:(1)在干旱区,当地下水位大于2m时,芦苇的光饱和点、表观量子效率、光呼吸速率随地下水位的下降显著降低,而水分利用效率却随着地下水位的下降呈上升趋势;随着地下水位的下降,芦苇的羧化效率、最大净光合速率、CO2饱和点显著下降,水分利用效率随之增大;1.6m地下水位的芦苇相对于2.7m地下水位下芦苇的最大净光合速率、光饱和点、光补偿点、暗呼吸速率分别下降19.98%、40.61%、37%、74.56%。(2)在盐胁迫下芦苇的光合参数整体低于受干旱胁迫的参数;盐胁迫下的芦苇水分利用效率大于受干旱胁迫环境。(3)与陆生环境下的芦苇相比,渍水条件下芦苇的最大净光合速率、光饱和点、光补偿点分别下降41.32%、14.56%、55.55%。研究表明,提高空气CO2供应量可降低水分利用效率从而缓解芦苇盐胁迫伤害,并且可通过调节气孔开闭程度显著增加水生芦苇最大净光合速率,这种变化是植物自身对环境因素变化的生理性反馈和适应性选择对策的结果。     

Effects of moderate high-temperature stress on photosynthesis in three saplings of the constructive tree species of subtropical forest

During the exposition to moderate high-temperature stress, photosynthetic rates and fluorescence of chlorophyll a were measured with a photosynthetic measurement system (Li-Cor 6400) and leaf chamber fluorometer (Li-Cor6400 LCF), respectively, in leaves of saplings, sun-adapted species (Schima superba), shade-adapted species (Cryptocarya concinna), and in mesophytic plant (Castanopsis hystrix) (42°C). The results showed that moderate high-temperature stress led to a decrease in F_v/F_m, namely the primary photochemical quantum efficiency, indicating that moderate high-temperature stress causes a partial inhibition of PSII. It also showed that such an effect was more severe in the shade-adapted plant C. concinna than in the sun-adapted species S. superba. However, except for the sun-grown leaves of C. concinna, the moderate high-temperature stress increased the photosynthetic rate of leaves at high light intensity. Simultaneously, less photoinhibition was found to occur under high-light intensity, suggesting that the capacity of resistant-photoinhibition was stimulated by moderate high-temperature stress. The quantum yield of PSII (ϕ_PSII) decreased in the sun-grown leaves of S. superba and C. hystrix but did not show any significant change in leaves of the shade plant C. concinna and shade-grown leaves of sun plant S. superba or the mesophytic plant C. hystrix because they already had a very low ϕ_PSII under this condition. Moderate high-temperature stress led to a decrease in ϕ_PSII/ϕ_CO2 ratios, an estimate of the quantum requirement for CO₂ assimilation, in the sun plant S. superba and the mesophytic plant C. hystrix because they were associated with the dissipation of a lower fraction of excitation energy. However, no significant changes were found in shade plant C. concinna and in shade-grown leaves of the other examined plants. The effect of moderate high-temperature (42°C) on photosynthesis depends on species and leaf type (sun and shade leaves) in the saplings of subtropical broad-leaved trees.     

Effects of moderate high-temperature stress on photosynthesis in three saplings of the constructive tree species of subtropical forest

During the exposition to moderate high-temperature stress, photosynthetic rates and fluorescence of chlorophyll a were measured with a photosynthetic measurement system (Li-Cor 6400) and leaf chamber fluorometer (Li-Cor6400 LCF), respectively, in leaves of saplings, sun-adapted species (Schima superba), shade-adapted species (Cryptocarya concinna), and in mesophytic plant (Castanopsis hystrix) (42°C). The results showed that moderate high-temperature stress led to a decrease in F_v/F_>m, namely the primary photochemical quantum efficiency, indicating that moderate high-temperature stress causes a partial inhibition of PSII. It also showed that such an effect was more severe in the shade-adapted plant C. concinna than in the sun-adapted species S. superba. However, except for the sun-grown leaves of C. concinna, the moderate high-temperature stress increased the photosynthetic rate of leaves at high light intensity. Simultaneously, less photoinhibition was found to occur under high-light intensity, suggesting that the capacity of resistant-photoinhibition was stimulated by moderate high-temperature stress. The quantum yield of PSII (?_PSII) decreased in the sun-grown leaves of S. superba and C. hystrix but did not show any significant change in leaves of the shade plant C. concinna and shade-grown leaves of sun plant S. superba or the mesophytic plant C. hystrix because they already had a very low ?_PSII under this condition. Moderate high-temperature stress led to a decrease in ?_PSII/?_CO2 ratios, an estimate of the quantum requirement for CO2 assimilation, in the sun plant S. superba and the mesophytic plant C. hystrix because they were associated with the dissipation of a lower fraction of excitation energy. However, no significant changes were found in shade plant C. concinna and in shade-grown leaves of the other examined plants. The effect of moderate high-temperature (42°C) on photosynthesis depends on species and leaf type (sun and shade leaves) in the saplings of subtropical broad-leaved trees.     

三种高山杜鹃的光合生理生态研究

对大白花杜鹃（Rhododendron decorum）、云南杜鹃（R.yunnanense）和红棕杜鹃（R.rubiginosum）进行了气体交换、叶片性状等研究,以期了解三种杜鹃的光合生理特性及其对环境的适应。结果表明,三种杜鹃的光饱和光合速率（Pmax）与RuBP饱和最大羧化速率（Vc max）、光饱和最大电子传递速率（Jmax）和气孔导度（gs）呈极显著正相关（P≤0.01）,但仅Vc max存在显著的种间差异,说明三种杜鹃的光合能力主要受Vc max影响。叶氮含量、叶片氮在电子传递和在Rubisco中的分配均显著影响Vc max和Jmax。大白花杜鹃的LSP最低,LCP较高,对强光和弱光利用能力都不强,光适应范围较窄。云南杜鹃LCP最低,LSP和Pmax相对较高,对弱光或较强的光照均能利用,光照适应范围相对最广,光合适应能力最强;红棕杜鹃LSP和LCP均为最高,对强光环境的适应性最强。     

濒危植物长叶榧的光合生理生态特性

利用Li-6400 XT便携式光合作用仪对林窗、林缘、林下3种生境中的长叶榧(Torreya ackii)在春、夏、秋、冬4个季节里的光合生理生态指标进行测定,探讨3种生境中长叶榧光合能力的季节变化及其对不同光环境的响应,分析其濒危机制,为长叶榧的迁地保护和种群的繁衍复壮提供理论依据。结果显示:(1)林窗、林缘的长叶榧净光合速率(Pn)日变化在夏季呈"双峰"曲线,其它3个季节均呈"单峰"曲线;林下的Pn日变化在4个季节均呈"单峰"曲线。(2)3种生境中最大净光合速率(Pnmax)、光饱和点(LSP)、表观量子效率(AQY)、最大羧化速率(Vcmax)、最大电子传递速率(Jmax)、磷酸丙糖利用率(TPU)均为夏季最高,使得夏季有较强的光合作用能力,但夏季林窗、林缘的长叶榧出现光合"午休"现象,光补偿点(LCP)、暗呼吸速率(Rd)也较高,使得夏季林窗生境的长叶榧日均Pn明显低于于秋季,林缘的日均Pn与秋季差异不显著。(3)4个季节的日均Pn、Pnmax、LSP、Vcmax、Jma、TPU均为林窗最高,林窗与林下差异显著,表明长叶榧具有阳性植物的特点,适宜生长在光照较强的林窗生境。(4)在生长旺盛的夏、秋季,长叶榧的LSP比伴生物种低,LCP比伴生物种高,对光适应的生态幅度较窄;与伴生物种相比,长叶榧的Pn较低,光合能力较弱,在激烈的种间竞争中处于不利地位,可能成为其濒危的一个重要原因。     

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.     

Responses of leafing phenology and photosynthesis to soil warming in forest-floor plants

Phenological and physiological responses of plants to climate change are key issues to understand the global change impact on ecosystems. To evaluate the species-specific responses, a soil-warming experiment was conducted for seven understory species having various leaf habits in a deciduous forest, northern Japan; one evergreen shrub, one semi-evergreen fern, one summer-deciduous shrub, and four summer-green herbs. Soil temperature in the warming plots was electrically maintained 5 °C higher than control plots. Responses of leafing phenology highly varied among species: new leaf emergence of the evergreen shrub was delayed; senescence of overwintering leaves of the semi-evergreen fern was accelerated resulting in the shift to deciduousness; leaf shedding of the summer-deciduous shrub was accelerated. Among four summer-green species, only an earliest leaf-out species advanced growth initiation, but the period of growth season was not changed. Physiological responses to soil warming were also highly species-specific: the warming treatment increased the photosynthetic activity of the summer-deciduous shrub and one summer-green species, decreased that of the semi-evergreen fern, while other species did not show any changes in photosynthetic traits. Totally, the soil warming impacts on understory plants was apparent in spring. It was suggested that modification of snow conditions is important issue especially for plants with overwintering leaves. Responses of understory vegetation to climate change may highly vary depending on the composition of leaf habits in the cool-temperate forests.     

荆条叶性状对野外不同光环境的表型可塑性

光照是影响植物生长和分布的重要环境因子。对生长在野外5种不同光环境下(林外、阔叶林林缘、阔叶林林下、针叶林林窗和针叶林林下)的荆条的叶片进行取样研究,通过对光合作用光响应曲线、叶绿素荧光、叶绿素含量、叶片氮磷含量以及叶片形态的测量,来反映荆条对不同光环境的表型可塑性。研究结果表明,荆条叶片对于野外不同的光环境具有很好的适应机制,叶片功能性状受到结构性状的调节。低光下通过高的比叶面积(SLA)、单位质量叶绿素含量、光系统II最大量子产量,低的暗呼吸速率、光饱和点、光补偿点、叶绿素a,b的比值来提高对光能的利用效率,维持生长;高光下则通过与SLA有关的叶片结构的变化对光合作用进行调节。大多数的叶性状只受到日光照总量的影响,SLA的大小与日最高光强有关,可以对不同日变化模式的光照做出迅速的响应,是适应不同光照的敏感指标。尽管光照是不同光环境下影响荆条叶性状的主要环境因子,土壤养分含量同样会对叶性状产生影响,高土壤养分下的高叶长与叶柄长的比值体现了植物对资源获取和支撑结构之间分配的权衡。     

不同光强对两种桤木幼苗光合特性和抗氧化系统的影响

通过搭建荫棚设置3种不同的光强, 模拟森林幼苗生长的旷地(砍伐迹地)、林窗和林下光照环境(分别为100%、56.2%和12.5%的全光照), 比较研究了外来种台湾桤木(Alnus formosana)和乡土种桤木(A. cremastogyne)幼苗的叶形态、光合能力、热耗散和抗氧化酶的活性, 探讨了两树种幼苗对光强的适应及光保护策略。结果表明: 在3种光强下, 一定光强范围内随着光强的增加, 两种桤木幼苗的比叶重(LMA)、类胡萝卜素(Cars)、类胡萝卜素/叶绿素(Cars/Chl)和抗氧化酶(超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、抗坏血酸过氧化物酶(APX))活性升高, 最大净光合速率(P_max)、光饱和点(LSP)、光补偿点(LCP)和非光化学猝灭系数(NPQ)具有升高的趋势; Chl含量和瞬时光能利用效率(LUE)降低; 净光合速率(P_n)、气孔导度(G_s)、气孔限制值(L_s)升高, 胞间CO₂浓度(C_i)降低, 推测P_n降低的主要因素是非气孔限制, 表明两种桤木幼苗均能适应不同的生长光强。生长在相同光强下, 桤木幼苗光抑制现象比台湾桤木幼苗严重, 台湾桤木幼苗对光强适应能力较强。随着光照强度的增加, 台湾桤木幼苗NPQ增加不显著, 热耗散较少, 相同光强下P_max和抗氧化酶活性显著高于桤木幼苗, 而桤木幼苗随着光强的增加热耗散显著, 表明在光抑制时, 台湾桤木幼苗主要是通过提高P_max利用光能和抗氧化酶系统进行保护性调节, 桤木幼苗则通过天线系统非辐射耗散将过剩的光能以热能的形式消耗掉。     

CORRELATES OF LEAF OPTICAL PROPERTIES IN TROPICAL FOREST SUN AND EXTREME-SHADE PLANTS

Thirteen shade-adapted rain forest species were compared with twelve sun-adapted tropical forest species for correlates to leaf optical properties (described previously in Amer. J. Bot. 73: 1100–1108). The two samples were similar in absorptance of quanta for photosynthesis, but the shade-adapted taxa: 1) had significantly lower specific leaf weights, indicating a more metabolically efficient production of surface for quantum capture; 2) synthesized less chlorophyll per unit area; and 3) used less chlorophyll for capturing the same quanta for photosynthesis. The anatomical features that best correlate with this increased efficiency are palisade cell shape and chloroplast distribution. Palisade cells with more equal dimensions have more chloroplasts on their abaxial surfaces. This dense layer of chloroplasts maximizes the light capture efficiency limited by sieve effects. The more columnar palisade cells of sun-adapted taxa allow light to pass through the central vacuoles and spaces between cells, making chloroplasts less efficient in energy capture, but allowing light to reach chloroplasts in the spongy mesophyll. Pioneer species may be an exception to these two groups of species. Three pioneer taxa included in this study have columnar palisade cells that are extremely narrow and packed closely together. This layer allows little penetration of light, but exposure of the leaf undersurface may provide illumination of spongy mesophyll chloroplasts in these plants.     

SEASONAL PRIMARY PRODUCTION OF UNDERSTORY RHODOPHYTA IN AN UPWELLING SYSTEM1

The in situ primary production of three common under-story members of the Rhodophyta in South African west coast kelp beds was determined monthly for a year using dissolved oxygen techniques. Strong seasonal patterns of photosynthesis and respiration were evident in all three species. Net photosynthesis of all three species was greatest in spring (October) and lowest in winter (June). Increasing photosynthesis in late winter coincided with increasing ambient irradiance and photoperiod, whereas decreasing photosynthesis in summer was not explained by changes in the environmental parameters measured. We suggest that this may he due to an innate pattern related to some other seasonal plant activity such as reproduction. Seasonal P_max and I_k values reveal that the obligate understory species, B. prolifera and E. obtusa, are shade-adapted whereas G. radula, a low intertidal and shallow subtidal dominant, is sun-adapted. Low C: X ratios consistent with a high nutrient environment and high rates of productivity were found in all three species. Net photosynthesis to respiration (Pn:R) ratios were fairly constant for B. prolifera and E. obtusa, implying that then photosynthetic processes were governed more by seasonal variations in irradiance than by instantaneous light availability. The Pn: R ratio of G. radula was variable, suggesting that this species is more responsive to rapid fluctuations in irradiance and may therefore be adapted for rapid growth during periods of high irradiance.     

南亚热带常绿阔叶林林冠不同部位藤本植物的光合生理特征及其对环境因子的适应

对南亚热带常绿阔叶林中着生在林冠层不同部位的4种藤本植物(白背瓜馥木(Fissistigma glaucescens)、瓜子金(Dischidia chinensis)、蔓九节(Psychotria serpens)和山蒌(Piper hancei))的光合生理生态特性进行比较, 探讨着生在林冠不同部位的藤本植物的光合生理特性随光照、温度、湿度等变化的规律。结果表明, 鼎湖山南亚热带常绿阔叶林微生境由上至下发生了较大变化, 相对于林内, 冠层顶部具有高温、高光强、低湿度的特征。受这些变化的环境因子的影响, 着生在林冠不同部位的藤本植物之间的光合生理特征存在着较大差异: 着生于林冠层中上部的瓜子金和蔓九节的最大净光合速率分别为(2.9 ± 0.6)和(6.3 ± 1.3) μmol CO₂·m^-2·s^-1, 光饱和点为(168.5 ± 83.4)和(231.4 ± 147.8) μmol·m^-2·s^-1, 显著小于位于冠层下部的白背瓜馥木和山蒌的最大净光合速率值(8.9 ± 2.9)和(8.6 ± 2.3) μmol CO₂·m^-2·s^-1以及光饱和点值(491.6 ± 230.8)和(402.3 ± 112.8) μmol·m^-2·s^-1。瓜子金和蔓九节的光补偿点值为(16.1 ± 5.9)和(10.1 ± 5.7) μmol·m^-2·s^-1, 水分利用效率值为(11.5 ± 3.9)和(8.7 ± 1.6) μmol CO₂·mmol^-1 H₂O, 显著大于林内的白背瓜馥木和山蒌的光补偿点值(5.6 ± 1.9)和(5.4 ± 1.7) μmol·m^-2·s^-1以及水分利用效率值(6.7 ± 1.8)和(6.8 ± 1.3) μmol CO₂·mmol^-1 H₂O。这些光合生理指标的变化显示出植物对不同的温度、光照、湿度的适应, 是植物适应环境条件的重要表现。     

Linking light attenuation,sunflecks, and canopy architecture in mesic shrub thickets

Expansion of shrubs into grasslands is often accompanied by a reduction in understory light and an associated reduction of shade-intolerant species. However, effects of specific canopy architectural characteristics on the light environment under shrub thickets are unknown. Our objective was to determine what characteristics of canopy architecture most influence understory light in monospecific shrub thickets. We quantified understory light and canopy architecture for five shrub species in the eastern United States that have a history of expansion, and we used multiple regression to determine which canopy characteristics best predicted light attenuation and relative contribution of sunflecks. Measurements included leaf angle, leaf azimuth, branch bifurcation ratio, leaf area index (LAI), canopy depth (the vertical distance from the bottommost leaf to the top of the canopy), and leaf area density (LAD) as well as understory photosynthetic photon flux density (PPFD). The best predictor of light attenuation and the occurrence of sunflecks for all species was canopy depth. Multiple leaf and plant-level traits were correlated with canopy depth but not with LAI or LAD. The invasive shrub Elaeagnus umbellata had the lowest understory light levels of the species examined although LAI values for Morella cerifera and Rhododendron maximum were higher. Branch bifurcation ratios for E. umbellata were significantly higher than for other species and this likely contributed to the differences in light attenuation and suppression of sunflecks. The potential of shrubs to intercept light is primarily dependent on vertical distribution of leaves in the canopy which is itself correlated with fine-scale, species-specific variations in leaf display.     

Effect of water stress on leaf photosynthesis,chlorophyll content,and growth of oriental lily

The photosynthetic characterization of the oriental lily (Lilium) cv. Sorbonne and its response to increasing water stress were analyzed based on the net photosynthetic rate (P _n), stomatal conductance (g _s), intercellular CO₂ concentration (C_i), transpiration rate (E), water use efficiency (WUE), and stomatal limitation (Ls) in the Horqin Sandy Land of western China. A photosynthesis-PAR response curve was constructed to obtain light-compensation and light-saturation points (LCP and LSP), the maximum photosynthetic rates (P _max) and dark respiration rates (R _D). The growth of lilies in the pots was analyzed after anthesis. Various intensities of water stress (5, 10, and 20 days without water, and an unstressed control) were applied. The results indicated that drought stress not only significantly decreased P _n, E, g _s, photosynthetic pigment content (Chl a, Chl b, and Chl (a + b)) and increased intrinsic water use efficiency (WUE), but also altered the diurnal pattern of gas exchange. Drought stress also affected the photosynthesis (P _n)-PAR response curve. Drought stress increased LCP and R _D and decreased LSP and P _max. There were both stomatal and nonstomatal limitations to photosynthesis. Stomatal limitation dominated in the morning, whereas nonstomatal limitation dominated in the afternoon. Thus, drought stress decreased potential photosynthetic capacity and affected the diurnal pattern of gas exchange and P _n-PAR response curves, thereby reducing plant quality (lower plant height, flower length, flower diameter, and leaf area). Water stress is likely the main limitation to primary photosynthetic process in the lily. Appropriate watering is recommended to improve photosynthetic efficiency and alleviate photodamage, which will increase the commercial value of the lily in the Horqin Sandy Land.     

Seasonal changes in photosynthesis and nitrogen allocation in leaves of different ages in evergreen understory shrub <Emphasis Type="Italic">Daphniphyllum humile</Emphasis>

Seasonal changes in photosynthetic capacity, leaf nitrogen (N) content, leaf chlorophyll (Chl) content and leaf N allocation patterns in leaves of different ages in the evergreen understory shrub, Daphniphyllum humile Maxim, growing at a forest border and an understory site were studied. In current-year leaves at the understory site, the N and Rubisco contents increased from spring to autumn although their light-saturated photosynthetic rate at 22°C (P _max²²) remained stable, indicating that their mesophyll conductance rates declined as they completed their development and/or that they invested increasing amounts of their resources in photosynthetic enzymes during this period. In contrast, seasonal changes in P _max²² in current-year leaves at the forest border site were correlated with changes in Rubisco content. In 1-year old leaves at the understory site, P _max²² and contents of Chl, leaf N, and Rubisco remained stable from spring to autumn, while these parameters decreased in 1-year-old forest border leaves, indicating that N may have been remobilized from shaded 1-year-old leaves to sunlit current-year leaves. When leaves senesced at the forest border site the Rubisco content decreased more rapidly than that of light-harvesting proteins such as LHCII, suggesting that N remobilization from Rubisco may be more efficient, possibly because Rubisco has greater N costs and is soluble, whereas the light-harvesting proteins are membrane components.     

Light use efficiency of California redwood forest understory plants along a moisture gradient

We investigated photosynthesis of five plant species growing in the understory at three sites (1,170-, 1,600- and 2,100-mm annual moisture inputs), along the geographical range of coastal California redwood forest, to determine whether greater inputs of rain and fog at northern sites enhance photosynthetic utilization of fluctuating light. Measurements of understory light environment and gas exchange were carried out to determine steady state and dynamic photosynthetic responses to light. Leaf area index ranged from 4.84 at the 2,100-mm site to 5.98 at the 1,170-mm site. Maximum rates of net photosynthesis and stomatal conductance (g) did not vary appreciably within species across sites. Photosynthetic induction after a change from low to high light was significantly greater in plants growing in lower light conditions regardless of site. Photosynthetic induction also increased with the rate of g in diffuse light, prior to the increase to saturating light levels. Post-illumination CO₂ assimilation was the largest factor contributing to variation in C gain during simulated lightflecks. The duration of post-illumination photosynthetic activity, total CO₂ assimilation per light received, and light use efficiency during simulated lightflecks increased significantly with moisture inputs in four out of five species. Increasing leaf N concentration with increasing moisture inputs in three out of five species, coupled with changes in leaf N isotopic composition with the onset of the summer fog season suggest that natural N deposition increases with rain and fog inputs and contributes to greater utilization of fluctuating light availability in coastal California redwood forests.     

Niche differentiation with respect to light utilization among coexisting dwarf shrubs in a subarctic woodland

Summary Canopy structure, shoot design, and photosynthetic light recruitment were used to compare four coexisting dwarf shrub species with respect to light utilization. All four species showed different shoot designs which probably result in different light interception properties. Leaves of Vaccinium uliginosum showed the highest levels of photosynthetic light saturation but in situ the shoots of this species reached their maximum photosynthetic rate at the lowest photon flux densities. No consistent differences with respect to photosynthetic light responses were found between deciduous and evergreen species. At sites dominated by one of the deciduous species (Vaccinium uliginosum or V. myrtillus), the two evergreen species studied (V. vitis-idaea and Empetrum hermaphroditum) occurred in the understory, i.e., with their leaf distribution slightly below that of the deciduous species. Sites dominated by one of the evergreen species showed less vertical differentiation in leaf distribution between species.