Efficient use of strong light for high photosynthetic productivity: interrelationships between the optical path,the optimal population density and cell-growth inhibition

The interrelationships between the optical path in flat plate reactors and photosynthetic productivity were elucidated. In preliminary works, a great surge in photosynthetic productivity was attained in flat plate photoreactors with an ultra short (e.g. 1.0 cm) optical path, in which extremely high culture density was facilitated by vigorous stirring and strong light. This surge in net photosynthetic efficiency was associated with a very significant increase in the optimal population density facilitated by the very short optical path (OP). A salient feature of these findings concerns the necessity to address growth inhibition (GI) which becomes increasingly manifested as cell concentration rises above a certain, species-specific, threshold (e.g. 1-2 billion cells of Nannochloropsis sp. ml(-1)). Indeed, ultrahigh cell density cultures may be established and sustained only if growth inhibition is continuously, or at least frequently, removed. Nannochloropsis culture from which GI was not removed, yielded 60 mg(-1) h(-1), yielding 260 mg l(-1) h(-1) when GI was removed. Two basic factors crucial for obtaining maximal photosynthetic productivity and efficiency in strong photon irradiance are defined: (1) areal cell density must be optimal, as high as possible (cell growth inhibition having been eliminated), insuring the average photon irradiance (I(av)) available per cell is falling at the end of the linear phase of the PI(av) curve, relating rate of photosynthesis to I(av), i.e. approximately photon irradiance per cell. (2) The light-dark (L-D) cycle period, which is determined by travel time of cells between the dark and the light volumes along the optical path, should be made as short as practically feasible, so as to approach, as much as possible the photosynthetic unit turnover time. This is obtainable in flat plate reactors by reducing the OP to as small a magnitude as is practically feasible.     

Influence of shoot structure on light interception and photosynthesis in conifers

The influence of shoot structure on net photosynthesis was evaluated under field conditions for the central Rocky Mountain (United States) conifers Picea engelmannii (Parry ex Engelm.), Abies lasiocarpa ([Hook] Nutt.), and Pinus contorta (Engelm.). In all species, the greater number of needles per unit stem length on sun shoots correlated with a smaller silhouette leaf area to total leaf area ratio (STAR). Decreased STAR was due primarily to greater needle inclination toward the vertical, plus some needle mutual shading. However, photosynthesis expressed on a total leaf area basis did not decrease in sun shoots (lower STAR) but remained nearly constant at approximately 3 micromoles per square meter per second over a wide range of STAR (0.1 to 0.3). Relatively low light saturation levels of 200 to 1400 microeinsteins per square meter per second and diffuse light to 350 microeinsteins per meter per second maintained photosynthetic flux densities in inclined and/or shaded needles at levels comparable to those in unshaded needles oriented perpendicular to the solar beam. As a result, net CO₂ uptake per unit stem length increased as much as 2-fold in sun shoots (low STAR) in direct proportion to increasing needle density.     

生物组织中有限束宽光吸收的蒙特卡罗模拟

用蒙特卡罗法模拟了有限束宽均匀分布和高斯分布光在生物组织中的传播,分析了生物组织的光学参数及光源特性对光吸收分子的影响,结果表明：只要有效光吸收系数增加,最大光吸收率就会增加,光的侧向传输能力主要依赖于光的有效散射,光束宽度增加,辐照范围加宽,高斯光束的吸收分布的梯度更大。     

A scanning device for the double beam leitz interference microscope

Summary The Leitz double beam interference microscope and its microscope photometer attachment have been rebuilt to a scanning instrument. The wide separation between the reference and object beam enables measurements of optical path differences (opd) in relatively large microscopic objects or in closely packed smaller objects without difficulties caused by the lack of free space for the reference beam. This advantage can now be combined with that of a scanning device. Using the system developed integrated values of the opd and hence the dry mass content of heterogeneous microscopic objects can be determined.Scanning in interference contrast is carried out in the image plane with a 0.1 mm diaphragm driven by two direct current motors. The intensity of the light passing the diaphragm is kept constant by adjustment of the glass wedge in the reference beam by means of a servo system. The displacement of the wedge, being proportional to the opd between the microscopic object and the free background, is recorded and integrated. The final value given by the integrator is proportional to the dry mass of the microscopic object.     

Optimizing the population density inIsochrysis galbana grown outdoors in a glass column photobioreactor

Particularly high population densities are readily sustainable in newly designed glass column reactors. The optimal density ofIsochrysis galbana in these columns in summer was 4.6 g L^–1 dry algal mass at which value the highest sustainable productivity obtained was a record of 1.6 g L^–1 d^–1. The population density exerted a direct effect on productivity: The higher the light intensity, the more pronounced was the dependence of the output rate on the population density, variations of 10%± from the optimal density resulting in a significant decline in productivity. The population density had also a very significant effect on the course of photoadaptation which took place during the first days after transferring the cultures from the laboratory to the outdoors. The output rate was lower by 5 to 35% on the first day of such transfer as compared to the light-adapted control. The higher the cell density, the faster was the process of photoadaptation as indicated by the rise of the productivity and O₂ tension to the control level. The potential for excess light damages was most prominent in the column reactors used, in which the light path was much reduced compared with that in open raceways. Significant photoinhibition took place at below optimal population density (2.8–3.8 g L^–1), and when cell density was further reduced (1.9 to 1.1 g L^–1), exposure to full sunlight caused photooxidative death within a few hours. The pattern of O₂ concentration in the culture that emerged along the day served as a useful indicator of photolimitation.Author for correspondence     

蒙特卡罗模拟多束光辐照下生物组织中的光吸收分布

用蒙特卡罗方法模拟了均匀分布光和高斯分布光在生物组织内的传播。通过比较单束以及多束均匀分布光和高斯分布光照射下组织内的光子能量分布规律,分析了不同光源和光斑大小对光吸收分布的影响。结果表明:与均匀光束比较,高斯光束辐照时,激光能量较为集中,但侧向传播范围较窄。在总功率相同的情况下,使用单束大功率宽光源与多束功率较小的小光斑光源均能明显地增大光的侧向传播距离,但使用多束功率较小的小光斑光辐照时生物组织中的最大光吸收率增大。多束组合光源光束间距对光吸收分布影响很大。     

The functional ecology of shoot architecture in sun and shade plants of Heteromeles arbutifolia M. Roem., a Californian chaparral shrub

The functional roles of the contrasting morphologies of sun and shade shoots of the evergreen shrub Heteromeles arbutifolia were investigated in chaparral and understory habitats by applying a three-dimensional plant architecture simulation model, YPLANT. The simulations were shown to accurately predict the measured frequency distribution of photosynthetic photon flux density (PFD) on both the leaves and a horizontal surface in the open, and gave reasonably good agreement for the more complex light environment in the shade. The sun shoot architecture was orthotropic and characterized by steeply inclined (mean = 71^o) leaves in a spiral phyllotaxy with short internodes. This architecture resulted in relatively low light absorption efficiencies (E _A) for both diffuse and direct PFD, especially during the summer when solar elevation angles were high. Shade shoots were more plagiotropic with longer internodes and a pseudo-distichous phyllotaxis caused by bending of the petioles that positioned the leaves in a nearly horizontal plane (mean = 5^o). This shade-shoot architecture resulted in higher E _A values for both direct and diffuse PFD as compared to those of the sun shoots. Differences in E _A between sun and shade shoots and between summer and winter were related to differences in projection efficiencies as determined by leaf and solar angles, and by differences in self shading resulting from leaf overlap. The leaves exhibited photosynthetic acclimation to the sun and the shade, with the sun leaves having higher photosynthetic capacities per unit area, higher leaf mass per unit area and lower respiration rates per unit area than shade leaves. Despite having 7 times greater available PFD, sun shoots absorbed only 3 times more and had daily carbon gains only double of those of shade shoots. Simulations showed that sun and shade plants performed similarly in the open light environment, but that shade shoots substantially outperformed sun shoots in the shade light environment. The shoot architecture observed in sun plants appears to achieve an efficient compromise between maximizing carbon gain while minimizing the time that the leaf surfaces are exposed to PFDs in excess of those required for light saturation of photosynthesis and therefore potentially photoinhibitory. Received: 8 June 1997 / Accepted: 2 November 1997     

Effect of light-path length in outdoor flat plate reactors on output rate of cell mass and of EPA in Nannochloropsis sp.

The effect of light-path length (i.e. reactor width or thickness) of flat plate glass reactors on outdoor production of eicosapentaenoic acid (EPA) and cell mass of Nannochloropsis sp. was tested, using a range of light-paths from 1.3 to 17.0 cm. Volumetric productivity of cell mass and optimal, as well as maximal cell density which represents the highest sustainable cell density under the experimental conditions, decreased with increase in light-path. Daily areal output rate (g dry weight m⁻² day⁻¹) increased with increased light-path, in contrast with results obtained in similar reactors with Spirulina cultures, in which areal output rates increased when the light-path was reduced. Maximal areal productivity of Nannochloropsis sp. (12.8 and 22.4 g ash-free dry weight per day per m² of irradiated reactor surfaces, in winter and summer, respectively), reflecting maximal efficiency in light utilization, was obtained with the long light-paths, i.e. 10.4 and 17.0 cm. Increasing the light-path from 1.3 to 17.0 cm resulted in an increase in areal EPA productivity, from 66.7 to 278.2 mg m⁻² day⁻¹ in winter and from 232.1 to 515.7 mg m⁻² day⁻¹ in summer. This enhancement in areal productivity of EPA stems from increased productivity of cell mass which was associated with the increase in light-path. We concluded that the optimal light-path, which must be defined for each algal species, represents an important parameter which determines optimal culture density (i.e. resulting in the highest output rate of cell mass per irradiated reactor surface), as well as productivity of cell mass and cell products. Under our conditions the optimal light-path for culturing Nannochloropsis in vertical reactors was ca 10 cm.     

TrackBeam, a simple tool for estimating potential exposure to the solar beam underneath tree canopies

A simple tool, TrackBeam, for rapid in situ estimates of potential exposure to the solar beam of objects underneath tree canopies is presented, tested and demonstrated to be useful in insect conservation studies. The tool can be used whenever accurate data on sun exposure is of use e.g., in ecological studies of saproxylic insects. TrackBeam draws upon the principles behind the analysis of hemispherical photographs but its use is much less dependent on the weather at the time of sampling. It may be used for detecting canopy openings in directions corresponding to the solar path. Based on this, periods of time with potential beam exposure and/or the proportion of sky that is not obscured by canopy for objects such as dead wood may be estimated. The results of using TrackBeam compares well between operators and with the corresponding results of analysed hemispherical photographs. Results are presented which show that TrackBeam was successfully used to characterise the habitat light requirements of the saproxylic beetle Melanotus castanipes (Coleoptera: Elateridae).     

Extracellular polysaccharide production in outdoor mass cultures of Porphyridium sp. in flat plate glass reactors

This work concerns an attempt to develop large scalecultivation of Porphyridium sp. outdoors. Theimpact on cell growth and production of solublesulphated polysaccharides of light-path length (LP)was studied in flat plate glass reactors outdoors. TheLP of the plate reactors ranged from 1.3–30 cm,corresponding to culture volumes of 3–72 L. The sidewalls of all reactors were covered, ensuring similarilluminated surfaces for all reactors. Maximal daytemperature was maintained at 26 ±1 ^°C.Growth conditions of pH (7.5), stirring (withcompressed air) and mineral nutrients, were optimal.Maximal volumetric concentration of the soluble sulfated polysaccharide (1.32 g L^-1) was obtained in winter with the smallest light-pathreactor (1.3 cm ) at a cell density of 1.37 ×10¹¹cells L^-1. Under these conditions, theviscosity of the culture medium was also highest,being inversely proportional to the culture'slight-path. Highest areal concentration of solublepolysaccharides (60 g m^-2) and areal cell density(3.01 × 10¹²m^-2) was recorded in the 20 cmLP reactor, progressively lower values being obtainedas the light path became shorter. A similar patternwas obtained for the areal productivity ofpolysaccharides, the highest being 4.15 g m^-2day^-1 (considering the total illuminated reactorsurface), produced in the 20-cm LP reactor.The main sugar composition (i.e. xylose, galactose andglucose) of the sulfated polysaccharides was similarin all reactors. As viscosity increased with timeduring culture growth, there was a substantial declinein bacterial population. Cultivation throughout mostof the year provided good evidence that a light pathlength of 20 cm in flat plate reactors under theseconditions is optimal for maximal areal solublepolysaccharide production of Porphyridium sp.     

Pigeons in the sun: Thermal constraints of eumelanic plumage in the rock pigeon (Columba livia)

In wild vertebrates, several species exhibit eumelanic color polymorphism with the coexistence of dark and light morphs. The maintenance of such polymorphism suggests the existence of a selective balance between the morphs and a large body of literature has reported the costs and benefits of darker plumage coloration in birds. Among them, it has been suggested that melanin and dark plumage could entail high energetic costs especially under hot and sunny climates. However, to my knowledge, the thermal constraints of sun exposure have rarely been studied in polymorphic species. Here, we tested the impact of eumelanic plumage coloration on plumage and body temperatures, and evaporative cooling behavior in the polymorphic rock pigeon (Columbia livia). We experimentally exposed light and dark pigeons to direct sun radiation for 1 h while a few birds were maintained in the shade as controls. We found that sun exposure was associated with increased plumage temperature, and this effect was greater for darker pigeons. In addition, we found that sun exposure was also associated with higher cloacal temperature but for dark pigeons only. Finally, light and dark pigeons were more likely to show cooling evaporative behavior when exposed to sun and as their cloacal temperature increases. Altogether, these results suggest that darker pigeons may have a lower ability to cope with heat and solar radiations and that dark plumage can be associated with thermal costs in this polymorphic species.     

用于全眼段成像和视轴参数测量的四焦点开关光学相干断层扫描

本文演示了四焦点开关傅里叶域光学相干断层扫描系统用于全眼段成像和体内视轴参数(VAP)测量的可行性.使用包括不同厚度平行玻璃板的两个同步转盘来将探测光束的焦点位置从角膜以及晶状体的前部和后部切换到视网膜.该过程同时增加了参考光束的深度范围.这种多级聚焦的方法可以使探测光束完全聚焦在人眼的每个部分.初步实验表明,该方法可...     

Effects of solar ultraviolet radiation on the potential efficiency of photosystem II in leaves of tropical plants

The effects of solar ultraviolet (UV)-B and UV-A radiation on the potential efficiency of photosystem II (PSII) in leaves of tropical plants were investigated in Panama (9°N). Shade-grown tree seedlings or detached sun leaves from the outer crown of mature trees were exposed for short periods (up to 75 min) to direct sunlight filtered through plastic or glass filters that absorbed either UV-B or UV-A+B radiation, or transmitted the complete solar spectrum. Persistent changes in potential PSII efficiency were monitored by means of the dark-adapted ratio of variable to maximum chlorophyll a fluorescence. In leaves of shade-grown tree seedlings, exposure to the complete solar spectrum resulted in a strong decrease in potential PSII efficiency, probably involving protein damage. A substantially smaller decline in the dark-adapted ratio of variable to maximum chlorophyll a fluorescence was observed when UV-B irradiation was excluded. The loss in PSII efficiency was further reduced by excluding both UV-B and UV-A light. The photoinactivation of PSII was reversible under shade conditions, but restoration of nearly full activity required at least 10 d. Repeated exposure to direct sunlight induced an increase in the pool size of xanthophyll cycle pigments and in the content of UV-absorbing vacuolar compounds. In sun leaves of mature trees, which contained high levels of UV-absorbing compounds, effects of UV-B on PSII efficiency were observed in several cases and varied with developmental age and acclimation state of the leaves. The results show that natural UV-B and UV-A radiation in the tropics may significantly contribute to photoinhibition of PSII during sun exposure in situ, particularly in shade leaves exposed to full sunlight.     

Sustainable, High-Yielding Outdoor Mass Cultures of Chaetoceros muelleri var. subsalsum and Isochrysis galbana in Vertical Plate Reactors

Continuous cultures of Chaetoceros muelleri and Isochrysis galbana were grown outdoors in flat plate-glass reactors in which light-path length (LPL) varied from 5 to 30 cm. High daily productivity (13 to 16 g cell mass per square meter of irradiated reactor surface) for long periods of time was obtained in reactors in which the optical path as well as cell density were optimized. 'Twenty centimeters was the optimal LPL, yielding the highest areal productivity of cell mass (g m^–2d^–1), eicosapentaenoic acid, and docosahexaenoic acid, which was identical with that previously found for polysaccharide production of Porphyridium and not far from the optimal LPL affecting maximal productivity in Nannochloropsis species. Relating the energy impinging on a given reactor surface area to the appropriate number of cells showed that the most efficient light dose per cell, obtained with the 20-cm LPL reactor, was approximately 2.5 times lower than the light dose available per cell in the 5-cm LPL reactor, in which a significant decline in areal cell density accompanied the lowest areal output of cell mass. The most effective harvesting regimen was in the range of 10% to 15% of culture volume harvested daily and replaced with fresh growth medium, resulting in a sustainable culture density of 24 × 10⁶ and 28 × 10⁶ cells/ml of C. muelleri and I. galbana, respectively.     

Optimization of a flat plate glass reactor for mass production of Nannochloropsis sp. outdoors

The relationships between areal (g m(-2) per day) and volumetric (g l(-1) per day) productivity of Nannochloropsis sp. as affected by the light-path (ranging from 1.3 to 17.0 cm) of a vertical flat plate glass photobioreactor were elucidated. In general, the shorter the length of the light-path (LP), the smaller the areal volume and the higher the volumetric productivity. The areal productivity in relation to the light-path, in contrast, yielded an optimum curve, the highest areal productivity was obtained in a 10 cm LP reactor, which is regarded, therefore, optimal for mass production of Nannochloropsis. An attempt was made to identify criteria by which to assess the efficiency of a photobioreactor in utilizing strong incident energy. Two basic factors which relate to reactor efficiency and its cost-effectiveness have been defined as (a) the total illuminated surface required to produce a set quantity of product and (b) culture volume required to produce that quantity. As a general guide line, the lower these values are, the more efficient and cost-effective the reactor would be. An interesting feature of this analysis rests with the fact that an open raceways is as effective in productivity per illuminated area as a flat-plate reactor with an optimal light path, both cultivation systems requiring ca. 85 m(2) of illuminated surface to produce 1 kg dry cell mass of Nannochloropsis sp. per day. The difference in light utilization efficiency between the two very different production systems involves three aspects - first, the open raceway requires ca. 6 times greater volume than the 10 cm flat plate reactor to produce the same quantity of cell-mass. Second, the total ground area (i.e. including the ground area between reactors) for the vertical flat plate reactor is less than one half of that occupied by an open raceway, indicating the former is more efficient, photosynthetically, compared with the latter. Finally, the harvested cell density is close to one order of magnitude higher in the flat plate reactor, which carries economic significance. The advantage of vertical lamination of photoautotrophic cells provided by vertical plate reactors, is thereby clearly seen. The optimal population density (i.e. which results in the highest areal productivity) in the 10 cm plate reactor was obtained by a daily harvest of 10% of culture volume, yielding an annual average of ca. 12.1 g dry wt. m(-2) per day (on the basis of the overall illuminated reactor surfaces, i.e. front and back) or 240 mg l(-1) per day.     

Sudden exposure to solar UV-B radiation reduces net CO(2) uptake and photosystem I efficiency in shade-acclimated tropical tree seedlings

Tree seedlings developing in the understory of the tropical forest have to endure short periods of high-light stress when tree-fall gaps are formed, and direct solar radiation, including substantial UV light, reaches the leaves. In experiments simulating the opening of a tree-fall gap, the response of photosynthesis in leaves of shade-acclimated seedlings (Anacardium excelsum, Virola surinamensis, and Calophyllum longifolium) to exposure to direct sunlight (for 20-50 min) was investigated in Panama (9 degrees N). To assess the effects of solar UV-B radiation (280-320 nm), the sunlight was filtered through plastic films that selectively absorbed UV-B or transmitted the complete spectrum. The results document a strong inhibition of CO(2) assimilation by sun exposure. Light-limited and light-saturated rates of photosynthetic CO(2) uptake by the leaves were affected, which apparently occurred independently of a simultaneous inhibition of potential photosystem (PS) II efficiency. The ambient UV-B light substantially contributed to these effects. The photochemical capacity of PSI, measured as absorbance change at 810 nm in saturating far-red light, was not significantly affected by sun exposure of the seedlings. However, a decrease in the efficiency of P700 photooxidation by far-red light was observed, which was strongly promoted by solar UV-B radiation. The decrease in PSI efficiency may result from enhanced charge recombination in the reaction center, which might represent an incipient inactivation of PSI, but contributes to thermal dissipation of excessive light energy and thereby to photoprotection.     

Quantitative 3D Model of Light Transmittance Through Translucent Rocks Applied to the Hypolithic Microbial Community

In extreme desert environments, photosynthetic microorganisms often live on the buried undersides of translucent rocks. Computing the light level reaching these locations requires 3D modeling of a finite rock. We report on Monte Carlo calculations of skylight and sunlight transmission through a partially buried flat cylindrical rock using one billion photons per simulation. Transmitted light level drops inversely with increasing rock opacity, as expected for purely scattering media. For a half-buried rock with an extinction coefficient of 0.1 cm^?1 (opacity of 0.2), transmission at the bottom is 64 % for sunlight at a solar zenith angle of 60° and 82 % for skylight. Transmitted light level increases slowly with increasing scattering asymmetry factor of the rock independent of illumination or depth buried. Transmitted sunlight at zenith through a thick half-buried rock (opacity of 0.6) is six times brighter at the bottom than the subsurface sides. Skylight transmits equally to the subsurface sides and bottom. When the sun is not straight overhead, the sunward side of the rock is brighter than the underside of the rock. Compared to the sunlight transmitted to the bottom, transmitted sunlight inclined at 60° is 24 times brighter at the subsurface side towards the sun and 14 times brighter at the subsurface side 70° away from the sun. Transmitted sunlight emitted from zenith and skylight is uniformly bright at the bottom regardless of how deeply the rock is buried. Sunlight not at zenith transmits preferentially to the sunward bottom edge depending on the depth the rock is buried.     

Photosynthetic acclimation in eastern hemlock [Tsuga canadensis (L.) Carr.] seedlings following transfer of shade-grown seedlings to high light

 We studied photosynthetic acclimation of eastern hemlock [Tsuga canadensis (L.) Carr.] seedlings in the first month after sudden exposure of shade-grown seedlings to full sunlight. In a greenhouse experiment, seedlings were grown under full sun or 80% shade, and after 7 months, a sample of the shaded trees was transferred to full sun in the greenhouse. Photosynthetic responses of shaded, transferred, and sun trees were followed over the course of 26 days to track short to medium-term acclimation responses. A partial acclimation of photosynthesis at high light occurred in pre-existing (formed in the previous environment) and new foliage of transferred seedlings. This was associated with non-stomatal limitations to photosynthesis. Pre-existing foliage of transferred plants had a prolonged reduction in the ratio of variable to maximal fluorescence, and a limited capacity to adjust photochemical quenching or photosystem II quantum yield in the light to increasing light intensity compared to sun foliage, and apparently had some difficulty sustaining non-photochemical quenching. Seedling survival was only 58% among transferred seedlings, compared to 80% and 100% in the shade or sun groups, respectively. Photosystem II quantum yield in the light, and photochemical and non-photochemical quenching were similar between newly formed foliage of transferred and sun plants. These findings indicate that eastern hemlock depends strongly on the production of new foliage for photosynthetic adjustments to high light, and that development of photosynthetic competence may be a gradual process that occurs over successive foliar production cycles. Received: 12 May 1998 / Accepted: 27 July 1998     

Erythrocyte sedimentation rate II. Effects of tilt angle in saline solution

We have measured the sedimentation curves of swine erythrocytes in a physiological saline solution in inclined glass tubes. The curves are well fitted to the exponential type equation l = a[1 - exp(-bt)] for the tilt angle theta in the range of theta less than 80 degrees and hematocrits from 10 to 50%, where l and t are the medium length along the tube and the elapsed time from the sample injection, respectively. The coefficient a increases with theta and b is proportional to sin theta. The erythrocyte sedimentation rate ESR(theta) = (d l/dt)t----0 determined from the above empirical equation increases with the increase in sin theta roughly linearly. The experimental results are discussed with reference to the Ponder-Nakamura-Kuroda theory and some recent theories.     

明党参幼苗存活与生长对光照强度的响应

以濒危植物明党参低温催芽形成的幼苗和常温正常萌发的幼苗为对象,对其存活及形态、结构、生物量及其分配、生长速率等指标进行测定和分析.结果表明,明党参幼苗在较高光强（65％全光照）存活率最高,有利于幼苗建成,低光强存活率最低.低温催芽形成的幼苗和常温正常萌发的幼苗对光照强度的响应规律类似,明党参幼苗的生长参数（株高除外）叶生物量、根生物量、总生物量、生长速率和总叶面积均在65％全光照条件下达到最大值,表现出最佳生长状况,表明适宜明党参幼苗生长的光照条件是65％全光照;利用低温催芽形成的幼苗生物量约是常温正常萌发幼苗的5倍,能提高其经受不利环境的能力,为明党参的栽培和保护提供一种新的途径.