Two-dimensional solar radiation interception model for hedgerow fruit trees

A two-dimensional, hourly or daily time step model was developed, which takes canopy characteristics and row orientation into account to simulate solar radiation interception in hedgerow orchards. In order to determine the spatial and temporal distribution of soil irradiance across the tree row, the canopy path length through which the radiation must travel to reach a certain point on the soil surface is calculated. The model assumes leaves to be uniformly distributed within an ellipsoid, and radiation penetrating the canopy is attenuated according to Beer’s law. Beam or direct radiation and diffuse radiation for the PAR (photosynthetically active radiation) and NIR (near-infrared radiation) wavebands are calculated separately, as they interact differently with the canopy. The attenuation of beam radiation by the canopy is strongly dependent on canopy dimensions and architecture, zenith and azimuth angle, as well as row orientation. Radiation can penetrate neighbouring rows, so two rows on either side of the simulated row are considered. Validation of the model was carried out for a wide range of conditions (crops, row orientation, canopy density, tree size and shape). Field measurements included solar radiation, soil irradiance at different distances from the tree row with tube solarimeters, leaf area density, as well as canopy size and row orientation. Model predictions of soil irradiance were excellent in orchards with symmetrical and elliptical canopies having a uniform leaf distribution. In orchards where the canopy was non-symmetric and/or had non-uniform leaf distribution, errors in predictions of solar radiation transmittance occurred. As a result of these discrepancies, the overall MAE was 40% of the average measured value of radiant transmittance over the whole day.     

利用3D模型模拟天空与叶面散射对玉米冠层截光率的影响

该文利用并行蒙特卡罗光线跟踪模型定量分析了天空散射与叶片散射对玉米冠层截光率的影响.模拟试验表明:相同辐射强度时,冠层截获的光强与受剑照射的叶片在天空散射时都比直接辐射时多;当太阳高度角小于60°时,冠层在阴大截获的总光强小于晴大,但至少60%的叶片在阴大截获的光强大于晴大时截获的光强;叶片散射对冠层光分布的影响与波长...     

基于夏玉米冠层内辐射分布的不同层叶面积指数模拟

为了模拟夏玉米冠层内各层叶面积指数垂直分布,光合有效辐射（photosynthetically active radiation, PAR）是研究作物群体光合作用和长势的重要特征参数,阐明冠层内PAR的垂直分布规律与冠层结构等参数之间的相关关系,可为遥感定量反演冠层结构参数提供模型基础。该文基于PAR在冠层内的辐射传输规律结合冠层结构模拟不同太阳高度角的PAR透过率垂直分布模型,并用地面冠层分析仪测量值进行验证,结果表明模型对封垄前玉米抽雄期冠层内PAR透过率垂直分布模拟精度较高。通过不同太阳高度角PAR透过率的垂直分布模型结合消光系数运用不同算法分别反演层叶面积指数（leaf area index, LAI）,并与不同高度层LAI实测值进行比较。结果显示：Bonhomme& Chartier算法反演不同高度层LAI精度较高,上层均方根误差（root mean square error,RMSE）为0.18,中层RMSE为0.55,下层RMSE为0.09。不同太阳高度角反演结果存在差异,30°和45°高度角均能较好地反演下层LAI,RMSE分别为0.11与0.09;30°高度角反演中层LAI精度较高,RMSE为0.30;45°高度角反演上层LAI精度较高,RMSE为0.18。结果表明基于不同太阳高度角构建的层LAI反演模型更适于实现夏玉米不同高度层LAI的遥感估算。该研究可为模拟垄行结构冠层内LAI垂直分布提供参考。     

Cotton responses to ultraviolet-B radiation: experimentation and algorithm development

The potential impact of an increase in solar ultraviolet-B (UV-B) radiation due to human activity on higher plants has been the subject of many studies. Little work has been carried out so far on cotton responses to enhanced UV-B radiation. The objective of this study was to determine whether or not the current and projected increases in UV-B levels affect cotton growth and development, and to quantify and develop UV-B radiation functional algorithms that can be used in simulation models. Two experiments were conducted during the summer of 2001 using sunlit plant growth chambers in a wide range of UV-B radiations under optimal growing conditions. Leaves exposed to UV-B radiation developed chlorotic and necrotic patches depending on the intensity and length of exposure. Along with changes in visible morphology, cotton canopy photosynthesis declined with increased UV-B radiation. The decline in canopy photosynthesis was partly due to loss of photosynthetic pigments and UV-B-induced decay of leaf-level photosynthetic efficiency (maximum photosynthesis) and capacity (quantum yield) as the leaves aged. The total leaf area was less due to smaller leaves and fewer leaves per plant. Less plant height was closely related to a shorter average internode length rather than a fewer mainstem nodes. The UV-B did not affect cotton major developmental events such as time taken to square, time to flower, and leaf addition rates on the mainstem. Lower biomass was closely related to both smaller leaf area and lower photosynthesis. The critical limit, defined as 90% of optimum or the control, for stem elongation was lower (8.7 kJ m⁻² per day UV-B) than the critical limit for leaf expansion (11.2 kJ m⁻² per day UV-B), indicating that stem elongation was more sensitive to UV-B than leaf expansion. The critical limits for canopy photosynthesis and total dry weight were 7 and 7.3 kJ m⁻² per day, respectively. The identified UV-B-specific indices for stem and leaf growth and photosynthesis parameters may be incorporated into cotton simulation models such as GOSSYM to predict yields under present and future climatic conditions.     

Evaluation of a radiosity based light model for greenhouse cucumber canopies

Light distribution is a key factor of developmental and growth processes, and strongly depends on the foliage distribution which is affected, e.g., by the arrangement of the plants in the canopy. The precise simulation of the light distribution on organ level is an essential component for dynamical plant models which incorporate structural and physiological adaptions of plants to their environment. Combinations of static 3D plant models with 3D light models are used for analyzing the complex light distribution on leaf level in silico, but detailed measurements for evaluation of simulation results are almost non-existent. This study addressed the evaluation of a model on a high level of detail using individual leaf based light measurements in canopies of cucumber (Cucumis sativus L.). We combined a static 3D plant model derived from digitized plants on an individual organ scale with a mock-up of the surrounding canopy and a 3D radiosity based light distribution model. Variations of plant density and spacing were analyzed to cover a range of canopy architectures. An exclusion of components of the light environment by applying a shading encasement followed by a successive uncovering allowed investigating the scene under increasing levels of complexity. The combined 3D plant-light distribution approach allowed determining the interaction of the light directions and the canopy architecture as well as differences in the accuracy of the simulations. Depending on canopy architecture and shading treatment, the light distributions covered a range from exponentially shaped vertical gradients in encased treatments to nearly flat light profiles in nonencased conditions. In conclusion, simulations of leaf level PAR based on combinations of detailed 3D surfaced-based plant and light distribution models are suitable to derive light-induced physiological responses on organ level.     

田间光照条件下应用半球图像解析玉米冠层结构参数

半球图像法是一种重要的作物冠层结构参数间接获取方法,该文针对半球图像法易受田间变化光照影响,提出一种基于多曝光图像融合映射的变化光照去除方法。首先,在田间条件下获取一组不同曝光值的冠层半球图像序列,然后通过图像亮度和曝光时间的线性方程组计算冠层的光照辐射强度图,而后采用直方图均衡化思想将不同时刻光照辐射强度图向RGB空间映射,映射后半球图像亮度均衡分布,消除光线变化对图像亮度的影响。在冠层参数解析阶段,利用Beer-Lambert定律反演玉米半球图像冠层叶面积指数(leaf area index,LAI)和平均叶倾角(mean leaf angle,MLA)的计算方法。试验结果表明,变化光照条件下半球图像冠层参数解析方法与直接测量法具有较高的相关性,LAI测量相关系数为0.970。该方法扩展了半球图像法的适用范围,为田间环境下冠层参数的自动连续监测提供了解决方案。     

Foliage area and architecture of plant canopies from sunfleck size distributions

A Poisson model is developed to describe sunfleck or gap size distributions beneath clumped plant canopies. This model is based on the assumption that foliage clumps are randomly distributed in space and foliage elements are randomly distributed within each clump. Using this model, the foliage clumping index, leaf area index (L), clump area index, element area index in each clump, and element and clump widths were successfully derived for two artificial canopies and a thinned and pruned Douglas-fir forest stand. It is shown that existing theories for deriving L from measurements of canopy gap fraction have limitations, and the use of canopy architectural information derived from canopy gap size distribution can substantially improve the technique for indirectly measuring L of plant canopies.     

UV-B辐射增强对大麦生理生态的影响

在大田条件下,研究了UV-B辐射增强对大麦的生长发育、光合作用、蒸腾作用及其产量构成的影响。结果表明,UV-B辐射增强明显抑制大麦生长,使株高变矮、绿叶数减少、叶面积和干物质量下降,但抑制程度随生育期而异。在UV-B辐射增强条件下,大麦叶片叶绿素含量、净光合速率、气孔导度和蒸腾速率都有不同程度的降低,水分利用率也随之降低。UV-B辐射增强对大麦形态学和生理学上的不利影响,导致了大麦产量下降24.96%。     

Ecosystem UV-B experiments in terrestrial communities: a review of recent findings and methodologies

Ecosystem-level UV-B experiments have revealed a variety of responses in terrestrial communities. These include decreases in the growth of some plant species (usually small changes but occasionally >25%), both decreases and increases in herbivory, occasional altered decomposition patterns, changes in populations of fungi and invertebrates, and morphological changes in the growth patterns of mosses. These field experiments have been pursued both with solar UV-B exclusion using selective filters and with supplementation of UV-B using lamps. For UV-B-exclusion studies it is critical that the UV-B-excluding and UV-B-transmitting filters pass the same amount of photosynthetically active radiation (PAR, 400–700 nm) and also infrared. Canopy photosynthesis models indicate that even small differences in PAR transmittance can, under many circumstances, have significant effects on plant carbon gain. It is also important that filters in UV-B-exclusion studies allow precipitation to pass uniformly to the plots unless there is some form of irrigation underneath the filters. For UV-B-supplementation studies with lamps, many factors are involved in the realism of the ozone depletion simulation. We believe the major lamp-system error is excessive supplementation of UV-B by timer-controlled lamps when weather conditions (primarily clouds) decrease ambient solar UV-B irradiance. The choice of biological spectral weighting functions (BSWF) used in adjusting lamp flux is also critical in determining the level of ozone depletion simulated. In addition, shading by the lamp arrays influences plant growth and becomes particularly important when BSWF with substantial weighting in the UV-A are employed.     

Impact of enhanced ultraviolet-B irradiance on cotton growth, development, yield, and qualities under field conditions

The stratospheric ozone depletion and enhanced solar ultraviolet-B (UV-B) irradiance may have adverse impacts on the productivity of agricultural crops. The effect of UV-B enhancements on agricultural crops includes reduction in yield, alteration in species competition, decrease in photosynthetic activity, susceptibility to disease, and changes in structure and pigmentation. Many studies have examined the influence of supplemental UV-B irradiance on different crops, but the effect of UV-B irradiance on cotton (Gossypium hirsutum L.) crops has received little attention. Cotton is one of the most versatile of all the crops. It is a major fiber crop of the world and a major source of trade and economy in many countries. In this study, we provide quantitative examination of the effects of elevated UV-B irradiance on cotton plant (Sukang 103). The tested cotton crop was grown under natural and four regimes of supplemental UV-B irradiance in the field. With UV-B irradiance increased 9.5% throughout the growing season, the negative impacts on cotton growth included reductions in height of 14%, in leaf area of 29%, and in total biomass of 34%. Fiber quality was reduced and economic yield dropped 72%; an economic coefficient was reduced 58%. A brief discussion is included on how the impacts on cotton contrast with impacts that have been observed in other studies on other plants, including trees.     

Field crop responses to ultraviolet-B radiation: a review

This paper provides an overview of existing literature on the ultraviolet-B (UV-B) radiation effects on field crops. Earlier reviews on field crop responses to UV-B considered few physiological processes or crops. For this review, we easily located about 129 studies on 35 crop species published since 1975. Here, we report the effects of UV-B radiation on visual symptoms, leaf ultrastructure and anatomy, photosynthetic pigments, UV-B absorbing compounds, photosynthesis, growth and development, yield, genotypic differences, and finally, interactions of UV-B with abiotic and biotic factors of crop plants. Experiments conducted in glasshouses, in closed and open top chambers, and under field conditions, with varying source (solar or artificial) and intensity of photosynthetically active radiation (PAR, 50–1800 μmol m⁻² s⁻¹) and UV-B (0–50 kJ m⁻² per day) are included. It is easy to conduct experiments that purport to evaluate the effects of projected UV-B intensities on crop species by providing supplemental irradiance with lamps or by reducing UV-B with filters; however, it is very difficult to simulate UV-B irradiance spectral changes that are likely to occur in nature. Collated results for each process are presented as percent change from control along with the experimental conditions in tabular format. Many of the studies showed dramatic effects of UV-B radiation, but under conditions with supplemental UV-B irradiance that was higher than would ever occur outside experimental conditions or in which the longer wavelengths in the PAR and UV-A, which moderate UV-B effects, were greatly reduced. Only 25 of the studies reviewed used experimental conditions and supplemental UV-B irradiance that approached realism. However, unrealistic the experimental conditions might be, an increase in understanding of basic plant physiology was gained from most of the studies.Visual symptoms consisting of chlorotic or necrotic patches on leaves exposed to UV-B were not unique. Both vegetative and reproductive morphology were altered by UV-B radiation. Leaf anatomy was altered due to changes in thickness of epidermal, palisade, and mesophyll layers. Enhanced UV-B generally decreased chlorophyll content (10–70%), whereas it increased UV-B absorbing compounds (10–300%) in many crops. Decrease in photosynthesis (3–90%), particularly at higher UV-B doses, was due to both direct (effect on photosystem) and indirect (decrease in pigments and leaf area) effects. The decreases in chlorophyll pigments and photosynthesis resulted in lower biomass and yield of most crop plants. Genotypes of crop species exhibited variability in leaf wax layer thickness, loss of chlorophyll, and increase in phenolics as mechanisms of tolerance to enhanced UV-B radiation resulting in changes in biomass/yield. Results from the few studies on interaction of UV-B with other abiotic and biotic factors did not lead to useful conclusions. Studies are needed to quantify the effects of UV-B radiation on crops in order to develop dose response functions that can facilitate development of dynamic simulation models for use in UV-B and other environmental impact assessments.     

Diffuse PAR irradiance under clear skies in complex alpine terrain

The diffuse component of photosynthetically active radiation (PAR) is important for models that calculate carbon dioxide uptake in photosynthesis by vegetation. Few PAR measurements are usually available, especially in complex terrain. Thus, extrapolation based on models becomes the primary means for deriving diffuse PAR in complex terrain. Most models treat the diffuse PAR sky distribution isotropically to avoid complex calculations. However, this leads to errors in diffuse PAR estimation due to the anisotropic nature of PAR sky radiance distribution. This paper describes a model for estimating diffuse PAR at any given point within complex terrain from measurements at a reference site, by taking into account both the anisotropic nature of sky radiance distribution and topographic effects. The model has been validated using two different sites, Kederbichl, and Bartholomä in the National Park Berchtesgaden, Germany, with Schönau as the reference site. The results revealed, that by replacing the isotropic treatment with PAR sky radiance distribution modified from the sky radiance distribution function in the model MURAC, the simulation accuracy is greatly improved. The R² of measured to modelled diffuse PAR reached 0.64 and 0.65 at Kederbichl and Bartholomä sites, respectively, compared to the isotropic treatment of 0.14 and 0.33. The normalized root mean square error (NRMSE) also improved from 0.47 to 0.23 and 0.40 to 0.26 for the Kederbichl and Bartholomä sites. An analysis of the ratio of diffuse radiation on slope to that on the horizontal (R_d) with solar zenith angle and the Linke turbidity factor indicated that R_d varies over time. Moreover, the variations of R_d are quite different at the above two sites, suggesting that R_d varies spatially as well. Overall, R_d in complex terrain is jointly controlled by diffuse sky radiance distribution and topography. Different combinations of topographic and atmospheric conditions will alter time dependent patterns in R_d. This casts doubt on the commonly held view that R_d can be assumed to be constant for radiation models.     

The bare bones of leaf-angle distribution in radiation models for canopy photosynthesis and energy exchange

The effects of leaf-angle distribution in radiation models for canopy photosynthesis and energy exchange can be accurately described by using as few as three leaf-angle classes (0–30°, 30–60° and 60–90°). On this basis, simple equations have been developed and tested for reflectance, extinction and distribution of radiation in leaf canopies. In these equations the spherical leaf-angle distribution, default in most models, serves as a point of reference.     

The distribution of leaf area,radiation, photosynthesis and transpiration in a Shamouti orange hedgerow orchard. Part II. Photosynthesis,transpiration, and the effect of row shape and direction

The influence of the distribution of radiation in an orange canopy on transpiration and photosynthesis was examined by developing a model of these processes.The leaf energy balance, microclimate relationships and climatic data are combined with radiation, leaf conductance, and leaf carbon uptake models to simulate orchard photosynthesis and transpiration over 2 days. Calculated hourly values of transpiration showed good agreement with measured values of sap flow in the orange orchard.Calculated carbon uptake during the six summer months was 22 kg CO₂ per tree; however, experimental estimates of annual dry matter production yield 55 kg CO₂ per tree. The calculated figure is therefore considerably in error and indicates that present information used in carbon balance modeling of Citrus is inadequate. Even so, it is shown that radiation levels deep in the canopy, where a significant amount of leaf area and transpiration is located, are too low for significant carbon uptake to occur.As an example of the usefulness of the model, the distributions of photosynthesis, transpiration and photosynthetic radiation were simulated in hedgerow canopies of three different shapes following current pruning practices in Israel. The distribution of foliage inside the given hedgerow cross-section was calculated based on the relationship of average measured foliage density to calculated diffuse photosynthetic irradiance in the canopy. The simulation was run for rows oriented north-south and east-west and for climatic conditions of midsummer. The results of the simulation indicated that: (a) The highest photosynthesis in citrus orchards is obtained by covering the largest ground areas possible with a thick canopy, i.e., maximum leaf area index (LAI). Under such conditions most photosynthesis occurs in the upper 1 m of the canopy. (b) Although rows with slanted walls do not have the highest photosynthesis, they allow more light penetration into the canopy and have productive regions on the periphery of the canopy at all heights within the orchard. (c) Whereas row orientation has little influence on total photosynthesis of the orchard, a N-S orientation allows more light penetration into rows with slanted walls and/or wide inter-row alleys, thus reducing spatial variation in the computed photosynthesis. (d) Water use of vertically pruned citrus orchards can be decreased significantly without seriously affecting photosynthesis by reducing canopy height to as low as 3 m.     

Digital measurement of heliotropic leaf response in soybean cultivars and leaf exposure to solar UVB radiation

Inconsistencies in reported sensitivities of soybean cultivars [Glycine max (L.) Merr.] to enhanced ultraviolet-B (UVB) irradiance may in part be due to differences in the radiative environment of the experimental conditions or differences in exposure due to heliotropic response. In order to examine the impact of heliotropic movement on UVB exposure of the soybean upper trifoliate, leaf position was electronically recorded and inclination and azimuthal position of the leaves calculated for three soybean cultivars—Bay, York, and Williams 82—under greenhouse and field conditions. The UVB exposures of the top trifoliate of three soybean cultivars were modeled using anisotropic and isotropic sky radiance distributions. The Williams 82 cv. produced the greatest variation in leaf angle with solar zenith angle of the three cultivars, averaging between 19 and 47°, compared with a lower 10–27° range for York and Bay cultivars. The incidence angle data for the upper trifoliates of the field plants were not significantly different from the greenhouse plants. For clear sky conditions, overall exposure differences indicated that the Bay cultivar receives more UVB than the York or Williams 82 cultivars, in large part due to the higher variation in heliotropic movement shown by the Bay cultivar in response to the sun location.     

UV-B辐射对植物水分代谢的影响

为系统了解UV-B辐射对植物水分代谢的影响, 本文从生理、生化两个角度概述了近30年国内外相关方面的研究成果, 内容涉及UV-B辐射对植物根系活力、蒸腾速率、水分利用效率及植物不同发育期叶片脯氨酸、可溶性糖含量的影响;总结了UV-B辐射对植物气孔行为的影响及相关机理, 包括植物体内ABA、H2O2、NO等信号分子含量的变化以及这些信号分子在调节气孔行为方面发挥的作用.认为UV-B辐射对植物水分代谢产生伤害, 且此伤害作用与植物种类、发育阶段有关, 与UV-B辐照时间及剂量正相关.研究UV-B辐射对植物水分代谢的影响, 对自然及农业生产环境下规避UV-B辐射对植物产生逆境胁迫效应具有积极的环境生态学价值.     

近期激光对植物生长调节效应的研究进展

分析了激光对植物生长调节效应的研究进展,发现研究明显具有以下特点:早期研究主要集中在激光预处理种子对种子萌发、幼苗生长发育、生理生化效应的影响以及激光处理机制的初步讨论;近年来的研究集中于激光处理对环境胁迫下植物生理生化效应影响,环境胁迫因子涉及增强UV-B辐射、干旱与冷冻,其中多数研究集中于激光对增强UV-B辐射下植物生理生化效应的影响,发现激光能增强植物抗UV-B辐射损伤,提高植物抗干旱逆境及抗冷冻能力,并对其作用机理及机制进行了探讨。今后可围绕全球生态环境变化背景下,激光处理对植物生理生化效应的影响进行研究,并深入研究激光影响的分子生物学机制机理。     

Yield and yield formation of field winter wheat in response to supplemental solar ultraviolet-B radiation

The stratospheric ozone decrease has heightened concern over the ecological implications of increasing solar UV-B radiation on agricultural production and natural plant ecosystems. UV-B is absorbed, and can damage many important plant species through a variety of interacting mechanisms. The effects of enhanced UV-B exposure on yield and yield formation of winter wheat associated with photosynthetic activity and total biomass development were investigated in this study. The overall experimental design included three UV-B treatments (two supplemental UV-B treatments and an ambient level) with three replicates of each treatment. Results suggested that the supplemental UV-B can cause the decrease of yield of winter wheat up to 24% with 11.4% increased UV-B. Supplemental UVB decreased dry matter accumulation most during the jointing–booting stage when the leaf area index (LAI) was the greatest. In addition, the supplemental U-VB appeared to effect the distribution of dry matter but did not effect the net assimilation ratio of the wheat.     

日光温室黄瓜非均质冠层光合生产的模拟

用均质冠层结构的光合模型来模拟非均质的日光温室黄瓜冠层光合速率则误差较大.该文所建立的日光温室黄瓜非均质冠层光合速率模型考虑到日光温室黄瓜冠层内光照分布以及叶片光合特性的不均匀性,其包含了非均匀冠层的透光模型和描述冠层叶片光合特性差异的经验公式.利用该模型对冠层光照分布和冠层光合速率的模拟结果表明:当模拟时所取的植株高度小于1.2 m,则冠层内直射光透光率和散射光透光率的模拟结果与验证值相比符合程度较好,但是对于模拟冠层单位体积内叶面积的总光合速率的结果还有待于进一步的验证.     

Tundra plants protect the soil surface from UV

In the Arctic, seasonal ozone depletion is resulting in periods of enhanced UV-B radiation at ground level while regional climate change is associated with increasing temperatures. These changes are likely to alter plant distribution, biodiversity and morphology, which may have knock-on effects for microbially driven biogeochemical cycling and other soil processes. Our study examined the transmission of solar UV radiation through arctic tundra plants using a portable UV radiometer and the DLR-biofilm biological UV dosimeter. A strong negative correlation was found between vegetation cover and UV transmission to the soil surface. Penetration of UV to the soil beneath tundra plants varied depending upon plant morphology, being greater through low creeping plants than cushion plants, grasses or mosses. UV transmission to the soil surface beyond the foliage edge also varied with plant morphology and the presence of flowers.