Influence of cold soil and snowcover on photosynthesis and leaf conductance in two Rocky Mountain conifers

Summary The influence of cold soil and snowcover on photosynthesis and conductance of Picea engelmannii and Pinus contorta was investigated early in the growing season in the Medicine Bow Mountains, Wyoming, USA. Trees of both species growing in cold soil (<1°C) associated with snowpack had 25–40% lower leaf photosynthesis than trees in warm soils (>10°C). In cold soils leaf conductance of both species was lower, but more so in Pinus, leading to lower intercellular CO₂ concentrations and greater stomatal limitation of photosynthesis. Soil temperature had no effect on predawn and midday shoot water potentials of Pinus and Picea and lower photosynthesis and conductance did not appear to be a result of lower bulk shoot water potential. Predawn, as well as midday, water potentials of Pinus were consistently higher than Picea suggesting that Pinus may have deeper roots, although trenching experiments indicated young Picea trees have more extensive lateral root systems than similar sized Pinus trees. Young Picea trees (<2 m in height) in snowbanks were capable of utilizing warmer soil 4 m from their base. Under similar conditions Pinus in snowbanks had lower photosynthesis and conductance than controls and Pinus did not appear capable of utilizing warmer soils nearby. Under full sunlight, PPFD reflected from the snow surface was 400–1400 mol m^-2 s^-1 higher than from snow-free surfaces. This reflected light resulted in a 10%–20% increase in photosynthesis of Picea. The beneficial effect of reflected light was apparent whether or not photosynthesis was reduced by low soil temperatures.     

Shoot structure, canopy openness, and light interception in Norway spruce

We analysed changes in shoot structure with canopy openness in control (C) and irrigated–fertilized (IL) Picea abies trees. Canopy openness, which was used to characterize light availability, varied between 0·23 and 0·90 for C shoots and 0·07 to 0·75 for IL shoots. Needle width and thickness increased with canopy openness, but were similar for C and IL needles. The ratio of needle thickness to width remained fairly close to one throughout the canopy. This resulted in large values (3·0–4·0) of the ratio of total to projected needle area. The ratio of total to projected needle area did not correlate with canopy openness. Shoot silhouette to total needle area ratio (STAR) and specific needle area decreased with canopy openness. As a result, shoot silhouette area per unit needle mass was up to three times larger in shade shoots than in sun shoots. STAR and specific needle area were similar for C and IL shoots and needles. Needle nitrogen concentration varied between 0·7 and 1·1% (C), and between 1·0 and 1·6% (IL). On both plots, nitrogen content was linearly related to estimated relative light interceptance (RLI) (both expressed per needle area), but the ratio of nitrogen content to RLI increased with decreasing canopy openness.     

Influence of light and temperature on photoinhibition of photosynthesis inSpirulina platensis

Photoinhibition of photosynthesis and its recovery in the cyanobacteriumSpirulina platensis was studied to find how photosynthetic rates were influenced by light and temperature. By exposing cell samples from a turbidostat culture to combinations of light and temperature, a connection between light, temperature and photoinhibition was found. The experiments showed that a 10 degree increase from 20 °C to 30 °C considerably reduced the photoinhibition. At 25 °C a photon flux density of 1720 µmol m^–2 s^–1 reduced the photosynthetic rate by 50 % in 1 h, but a similarly high photon flux density had nearly no negative effect at 35 °C. Reactivation in low light from 50% photoinhibition was fast and complete in 60 min at 30 °C, while at 20 °C only about 1/6 of the full capacity was regained in the same time. Addition of the protein synthesis inhibitor streptomycin to cultures undergoing photoinhibition and regeneration indicated the presence also in this organism of a repair mechanism based on protein synthesis.Author for correspondence     

Influence of light on adventitious root formation in birch shoot culturesin vitro

The influence of light of different spectral composition and levels of irradiance (2-40 Wm-²) on adventitious root formation (ARF) in birch shoot segments was investigated. Spontaneous rooting of shoot segments occurred in segments with intact apical or axillary meristems. Concerning ARF shoot meristems could be substituted by application of auxin. The very low rooting percentage of shoot segments in darkness was improved considerably by auxin application. Irradiation of cuttings was a requirement for a high percentage of spontaneous rooting. The promoting effect of light was dependent on its spectral composition and was the highest under red followed by white and blue light. The low rooting response under blue light was enhanced almost to the red light level by shielding the root-forming cutting base from light.     

Exploring the spatial distribution of light interception and photosynthesis of canopies by means of a functional-structural plant model

Background and Aims

At present most process-based models and the majority of three-dimensional models include simplifications of plant architecture that can compromise the accuracy of light interception simulations and, accordingly, canopy photosynthesis. The aim of this paper is to analyse canopy heterogeneity of an explicitly described tomato canopy in relation to temporal dynamics of horizontal and vertical light distribution and photosynthesis under direct- and diffuse-light conditions.

Methods

Detailed measurements of canopy architecture, light interception and leaf photosynthesis were carried out on a tomato crop. These data were used for the development and calibration of a functional–structural tomato model. The model consisted of an architectural static virtual plant coupled with a nested radiosity model for light calculations and a leaf photosynthesis module. Different scenarios of horizontal and vertical distribution of light interception, incident light and photosynthesis were investigated under diffuse and direct light conditions.

Key Results

Simulated light interception showed a good correspondence to the measured values. Explicitly described leaf angles resulted in higher light interception in the middle of the plant canopy compared with fixed and ellipsoidal leaf-angle distribution models, although the total light interception remained the same. The fraction of light intercepted at a north–south orientation of rows differed from east–west orientation by 10 % on winter and 23 % on summer days. The horizontal distribution of photosynthesis differed significantly between the top, middle and lower canopy layer. Taking into account the vertical variation of leaf photosynthetic parameters in the canopy, led to approx. 8 % increase on simulated canopy photosynthesis.

Conclusions

Leaf angles of heterogeneous canopies should be explicitly described as they have a big impact both on light distribution and photosynthesis. Especially, the vertical variation of photosynthesis in canopy is such that the experimental approach of photosynthesis measurements for model parameterization should be revised.     

The responses of light interception,photosynthesis and fruit yield of cucumber to LED‐lighting within the canopy

Mathematical models of light attenuation and canopy photosynthesis suggest that crop photosynthesis increases by more uniform vertical irradiance within crops. This would result when a larger proportion of total irradiance is applied within canopies (interlighting) instead of from above (top lighting). These irradiance profiles can be generated by Light Emitting Diodes (LEDs). We investigated the effects of interlighting with LEDs on light interception, on vertical gradients of leaf photosynthetic characteristics and on crop production and development of a greenhouse‐grown Cucumis sativus‘Samona’ crop and analysed the interaction between them. Plants were grown in a greenhouse under low natural irradiance (winter) with supplemental irradiance of 221 µmol photosynthetic photon flux m^?2 s^?1 (20 h per day). In the interlighting treatment, LEDs (80% Red, 20% Blue) supplied 38% of the supplemental irradiance within the canopy with 62% as top lighting by High‐Pressure Sodium (HPS)‐lamps. The control was 100% top lighting (HPS lamps). We measured horizontal and vertical light extinction as well as leaf photosynthetic characteristics at different leaf layers, and determined total plant production. Leaf mass per area and dry mass allocation to leaves were significantly greater but leaf appearance rate and plant length were smaller in the interlighting treatment. Although leaf photosynthetic characteristics were significantly increased in the lower leaf layers, interlighting did not increase total biomass or fruit production, partly because of a significantly reduced vertical and horizontal light interception caused by extreme leaf curling, likely because of the LED‐light spectrum used, and partly because of the relatively low irradiances from above.     

Effects of leaf age,elevation and light conditions on photosynthesis and leaf traits in saplings of two evergreen conifers,Abies veitchii and A. mariesii

亚高山的针叶树物种分布在广泛的海拔范围内,因此它们必须具备抵抗严酷自然条件(如高海拔和长期的黑暗)的能力。 在日本中部的亚高山地带,两种常绿的针叶树冷杉(Abies veitchii)和马尾冷杉(Abies mariesii)分别在低海拔和高海拔地区占据优势。本研究的目的是探讨叶龄、海拔和光照条件对两个物种叶片形态和生理性状的影响。我们以两种针叶树的幼树为样本,分别在两种针叶树下部 (1600米)和上部(2300米)的林下层和冠层间隙中取样,并分析叶龄、海拔和光照条件对冷杉和马尾冷杉的光合作用和叶片性状的影响。研究结果表明,两种针叶树的光合作用和叶片性状对叶龄呈现相似的响应,但其对海拔和光照条件则表现出不同的响应。冷杉最大光合速率与单位叶面积质量和非结构性碳水化合物浓度呈负相关。两种树木的单位叶面积质量在高海拔处均增加,而非结构性碳水化合物浓度仅在冷杉中增加。因此,冷杉的最大光合速率在高海拔时降低。此外,两个物种的最大光合速率均与氮浓度呈正相关。在林下层,叶片氮浓度在冷杉中下降,而在马尾冷杉中上升。在林下条件下,只有马尾冷杉的单位叶面积质量下降、叶绿素-氮比增加,表明在黑暗条件下,马尾冷杉比冷杉有更高的捕光效率。本研究表明,与冷杉相比,马尾冷杉的光合和叶片特性具有更强的耐阴性,光合速率受海拔的影响较小,从而使马尾冷杉在林下植被中生存,并在高海拔地区占据优势。     

Influence of light intensity,temperature and humidity on photosynthesis and transpiration ofSasa nipponica andArundinaria pygmaea

Photosynthesis and transpiration were simultaneously measured under different light intensity, temperature and humidity conditions inSasa nipponica andArundinaria pygmaea grown in exposed and shaded habitats. Both species showed a saturated light curve for photosynthetic rate. The saturation point was lower in shaded plants. The apparent quantum yields were larger inS. nipponica and in shaded plants, while the maximum photosynthesis was higher inA. pygmaea and exposed plants. The temperature response of photosynthesis showed an optimum curve in both species. The optinum temperatures were 20 C inS. nipponica and 25 C inA. pygmaea. The influence of humidity on photosynthesis was insignificant for both species. The responses of transpiration to light intensity and relative humidity showed a saturated curve and an optimal one, respectively. There was a significant relationship between transpiration and stomatal frequency, both of which were higher inS. nipponica, while water use efficiency was higher inA. pygmaea. These results suggest thatS. nipponica adapts itself better to shaded, low temperature and less water stress habitats as compared withA. pygmaea.     

Dynamics of photosynthesis in fluctuating light

Our understanding of the molecular mechanisms of plant photosynthesis is expanding from insights into static fluxes in constant irradiance to an understanding of complex dynamic patterns in fluctuating light. Knowledge about regulatory interactions, information about relevant biological features that emerge in fluctuating light, and the new standards for sharing biological models allow world-wide consortia aimed at the comprehensive modeling of photosynthetic dynamics.     

Row structure and foliage geometry as determinants of the interception of light rays in a sorghum row canopy

Abstract. The interception of light rays by the canopy of a widely spaced sorghum row crop was assessed from a series of hemispherical photographs taken on five occasions during its vegetative growth. Analysis of the photographs shows that most of the temporal and spatial variation in the canopy's interception could be accounted for by treating the row as an array of solid parallel walls with rectangular cross sections. Within the space occupied by rows, the effect of the distribution of foliage elements on interception could be assessed by the porosity of a single row. The north-south asymmetry observed in the distribution of ray interception indicates that this sorghum canopy, grown under unirrigated, arid summer conditions, adopted a light-avoiding growth pattern.     

叶片叶肉结构对环境光强的适应及对光合作用的影响

本文利用Kubelka-Munk理论描述了平行光在叶片内的吸收和散射,同时利用叶片分层光合作用非直角双曲线光反应模型,给出了整张叶片光合作用计算式。最后利用优化理论阐明了叶片叶肉分化成光合特性具有明显差异的栅栏组织和海绵组织可能是对叶片内光梯度的一种适应;同时证明了叶片叶肉在一定环境光强下存在一个最佳的栅栏组织和海绵组织比例,并且这个比例随环境光强增大而增大,这最佳比例也受叶肉组织光合特性差异的影响。     

Blue light effects on rose photosynthesis and photomorphogenesis

Through its impact on photosynthesis and morphogenesis, light is the environmental factor that most affects plant architecture. Using light rather than chemicals to manage plant architecture could reduce the impact on the environment. However, the understanding of how light modulates plant architecture is still poor and further research is needed. To address this question, we examined the development of two rose cultivars, Rosa hybrida‘Radrazz’ and Rosa chinensis‘Old Blush’, cultivated under two light qualities. Plants were grown from one‐node cuttings for 6 weeks under white or blue light at equal photosynthetic efficiencies. While plant development was totally inhibited in darkness, blue light could sustain full development from bud burst until flowering. Blue light reduced the net CO₂ assimilation rate of fully expanded leaves in both cultivars, despite increasing stomatal conductance and intercellular CO₂ concentrations. In ‘Radrazz’, the reduction in CO₂ assimilation under blue light was related to a decrease in photosynthetic pigment content, while in both cultivars, the chl a/b ratio increased. Surprisingly, blue light could induce the same organogenetic activity of the shoot apical meristem, growth of the metamers and flower development as white light. The normal development of rose plants under blue light reveals the strong adaptive properties of rose plants to their light environment. It also indicates that photomorphogenetic processes can all be triggered by blue wavelengths and that despite a lower assimilation rate, blue light can provide sufficient energy via photosynthesis to sustain normal growth and development in roses.     

Modelling the effects of elevated atmospheric CO2 on crown development, light interception and photosynthesis of poplar in open top chambers

An open-top chamber experiment was carried out to examine the likely effects of elevated atmospheric [CO₂] on architectural as well as on physiological characteristics of two poplar clones ( Populus trichocarpa × P. deltoides clone Beaupré and P. deltoides × P. nigra clone Robusta). Crown architectural parameters required as input parameters for a three-dimensional (3D) model of poplar structure, such as branching frequency and position, branch angle, internode length and its distribution pattern, leaf size and orientation, were measured following growth in ambient and elevated [CO₂ ] (ambient + 350 μmol mol^–1) treated open-top chambers. Based on this information, the light interception and photosynthesis of poplar canopies in different [CO₂] treatments were simulated using the 3D poplar tree model and a 3D radiative transfer model at various stages of the growing season. The first year experiments and modelling results showed that the [CO₂] enrichment had effects on light intercepting canopy structure as well as on leaf photosynthesis properties. The elevated [CO₂] treatment resulted in an increase of leaf area, canopy photosynthetic rate and above-ground biomass production of the two poplar clones studied. However, the structural components responded less than the process components to the [CO₂] enrichment. Among the structural components, the increase of LAI contributed the most to the canopy light interception and canopy photosynthesis; the change of other structural aspects as a whole caused by the [CO₂] enrichment had little effect on daily canopy light interception and photosynthesis.     

Green light drives photosynthesis in mosses

Temperate forests are characterised by variable light quality (i.e. spectral composition of light) at or near the forest floor. These understory environments have a high concentration of green light, as red and blue light are preferentially absorbed by upper canopy leaves. Understory species may be well-adapted for using green light to drive photosynthesis. Angiosperms have been shown to use green light for photosynthesis, but this ability has not been demonstrated in shade-dwelling bryophytes. In this study, net photosynthetic rate (P_N) of three temperate understory species of moss (Dichodontium pellucidum (Hedw.) Schimp., Leucobryum albidum (Brid. ex P.Beauv) Lindb. and Amblystegium serpens (Hedw.) Schimp.) was measured under green, red?+?blue, and red?+?blue?+?green light to assess green light use efficiency. All three species were capable of photosynthesising beyond their respiratory demands using solely green light, with higher green light use efficiency measured in plants collected from areas with greater canopy cover, suggesting growth in a green light concentrated environment increases green light use efficiency. Each species was also collected from sites differing in their degree of canopy cover and grown under three light treatments (high light, low light, and green light). Photosynthetic efficiency (chlorophyll fluorescence), tissue nitrogen and carbon isotope concentrations were assessed after a short growth period. Growth conditions had little effect on leaf chemistry and monochromatic green light did not significantly degrade photosynthetic efficiency. This study provides the first evidence to date of positive net ‘green light photosynthesis’ in mosses.     

Implications of shoot structure on the rate of photosynthesis at different levels in a coniferous canopy using a model incorporating grouping and penumbra

1. The connection between high leaf area index (LAI) and photosynthetic production with two attributes of coniferous canopy structure: small leaf size and grouping of needles on shoots, was analysed using a simulation model.
2. The small size of conifer needles gives rise to penumbras, which even out the distribution of direct sunlight on the leaf area and thereby act to increase the rate of canopy photosynthesis per unit of LAI.
3. Grouping, by producing a non-uniform distribution of leaf area, causes a decrease in total canopy light interception at any given LAI, but improves the photosynthetic light capture by shoots in the lower canopy.
4. Application of the model on a case study showed that: (a) grouping had a negative effect on the rate of photosynthesis in the upper canopy, but deeper down in the canopy the situation was reversed; (b) in the lower canopy, photosynthetic rates were up to 10 times higher as a result from the combined effect of grouping and penumbra; (c) grouping did not improve the rate of canopy photosynthesis per unit of LAI, however, it can have a positive effect on the total photosynthetic production by allowing a higher productive LAI to be maintained; (d) penumbra, on the other hand, increased the rate of canopy photosynthesis by as much as 40% for moderate values of the LAI.     

Effect of light interception by non-photosynthetic organs on canopy photosynthetic production

A canopy photosynthesis model was derived on the assumption that the light diminution within a canopy is caused by both leaves and non-photosynthetic organs. The light diminution by leaves and that by non-photosynthetic organs were taken into account separately in the Lambert-Beer equation of light extinction. The light flux density on the leaf surface at each depth was evaluated from the leaf's share of light. The light flux density on the leaf surface thus obtained was incorporated into the Monsi-Saeki model of canopy photosynthesis. The proposed model was applied for estimating gross canopy photosynthesis in a 19-year-oldLarix leptolepis plantation where 38% of the light diminution was due to non-photosynthetic organs. The daily canopy photosynthesis on one summer day calculated using the present model was about 22% less than that calculated by the conventional Monsi-Saeki model, in which light interception by non-photosynthetic organs is neglected. The degree of such reduction in canopy photosynthesis through shading by non-photosynthetic organs was assessed in relation to parameters affecting light extinction, leaf photosynthetic characteristics, and light regime above the canopy.     

叶幕PAR光能截留和分配对葡萄群体光合同化物源库关系的调控

 田间自然条件下在葡萄园群体水平上多年的研究证明：叶幕PAR光能截留率与葡萄群体净光合速率、叶幕和单叶PAR光能截留率与果实干物质总量占地上部生物量干重的百分比、与果实总糖产量占果实本身干物质总量的百分比、以及与果皮色素产量占果实本身干物质总量的千分比之间呈现显著或极显著的线性正相关关系。说明利用叶幕结构变异调节叶幕PAR光能截留和分配,可以对光合同化物源库关系和果实中物质代谢方向进行有效的调控。PAR光能截留率较高和分配合理的叶幕,不但通过较高的群体光合速率为产量和品质形成提供了丰富的同化物“源”,而且通过调节器官间“库”关系使同化物以较高的比例流向果实,同时使果实中物质代谢过程有利于合成构成品质的要素。     

Importance of the description of light interception in crop growth models

Canopy light interception determines the amount of energy captured by a crop, and is thus critical to modeling crop growth and yield, and may substantially contribute to the prediction uncertainty of crop growth models (CGMs). We thus analyzed the canopy light interception models of the 26 wheat (Triticum aestivum) CGMs used by the Agricultural Model Intercomparison and Improvement Project (AgMIP). Twenty-one CGMs assume that the light extinction coefficient (K) is constant, varying from 0.37 to 0.80 depending on the model. The other models take into account the illumination conditions and assume either that all green surfaces in the canopy have the same inclination angle (θ) or that θ distribution follows a spherical distribution. These assumptions have not yet been evaluated due to a lack of experimental data. Therefore, we conducted a field experiment with five cultivars with contrasting leaf stature sown at normal and double row spacing, and analyzed θ distribution in the canopies from three-dimensional canopy reconstructions. In all the canopies, θ distribution was well represented by an ellipsoidal distribution. We thus carried out an intercomparison between the light interception models of the AgMIP–Wheat CGMs ensemble and a physically based K model with ellipsoidal leaf angle distribution and canopy clumping (KellC). Results showed that the KellC model outperformed current approaches under most illumination conditions and that the uncertainty in simulated wheat growth and final grain yield due to light models could be as high as 45%. Therefore, our results call for an overhaul of light interception models in CGMs.