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.     

Optimality of nitrogen distribution among leaves in plant canopies

The vertical gradient of the leaf nitrogen content in a plant canopy is one of the determinants of vegetation productivity. The ecological significance of the nitrogen distribution in plant canopies has been discussed in relation to its optimality; nitrogen distribution in actual plant canopies is close to but always less steep than the optimal distribution that maximizes canopy photosynthesis. In this paper, I review the optimality of nitrogen distribution within canopies focusing on recent advancements. Although the optimal nitrogen distribution has been believed to be proportional to the light gradient in the canopy, this rule holds only when diffuse light is considered; the optimal distribution is steeper when the direct light is considered. A recent meta-analysis has shown that the nitrogen gradient is similar between herbaceous and tree canopies when it is expressed as the function of the light gradient. Various hypotheses have been proposed to explain why nitrogen distribution is suboptimal. However, hypotheses explain patterns observed in some specific stands but not in others; there seems to be no general hypothesis that can explain the nitrogen distributions under different conditions. Therefore, how the nitrogen distribution in canopies is determined remains open for future studies; its understanding should contribute to the correct prediction and improvement of plant productivity under changing environments.     

Photomodulation of axis extension in sparse canopies : role of the stem in the perception of light-quality signals of stand density

A fiber optic probe inserted into plant tissues was used to investigate the effects of canopy density on the light environment in different organs. The red:far-red ratio inside the stem of Datura ferox L. seedlings and the estimated phytochrome photoequilibrium were strongly reduced by the presence of neighbors forming canopies too sparse to cause any mutual shading at the level of the leaves. In such canopies, changes in plant density had little effects on the light regime inside the leaves of the succulent Aeonium haworthii (S.D.) Webb et Berth., particularly when the lamina was kept nearly normal to the direct rays of the sun. In field experiments using D. ferox and Sinapis alba L. seedlings, the elongation of the internodes responded to various types of localized light-quality treatments that simulated different plant densities in sparse canopies. The responses were quantitatively similar to those elicited by changes in plant density. The evidence supports the hypothesis that, in stands formed by plants of similar size, the red:far-red ratio of the light that impinges laterally on the stems is among the earliest environmental cues that allow plants to detect local canopy density and adjust axis extension accordingly.     

A simulation of the importance of length of growing season and canopy functional properties on the seasonal gross primary production of temperate alpine meadows

Background and Aims: Along snowmelt gradients, the canopies of temperate alpine meadowsdiffer strongly in their structural and biochemical properties.Here, a study is made of the effects of these canopy dissimilaritiescombined with the snow-induced changes in length of growingseason on seasonal gross primary production (GPP). Methods: Leaf area index (LAI) and community-aggregated values of leafangle and leaf nitrogen content were estimated for seven alpineplant canopies distributed along a marked snowmelt gradient,and these were used as input variables in a sun–shadecanopy bulk-photosynthesis model. The model was validated forplant communities of early and late snowmelt sites by measuringthe instantaneous CO₂ fluxes with a canopy closed-chamber technique.A sensitivity analysis was conducted to estimate the relativeimpact of canopy properties and environmental factors on thedaily and seasonal GPP. Key Results: Carbon uptake was primarily related to the LAI and total canopynitrogen content, but not to the leaf angle. For a given levelof photosynthetically active radiation, CO₂ assimilation washigher under overcast conditions. Sensitivity analysis revealedthat increase of the length of the growing season had a highereffect on the seasonal GPP than a similar increase of any otherfactor. It was also found that the observed greater nitrogencontent and larger LAI of canopies in late-snowmelt sites largelycompensated for the negative impact of the reduced growing season. Conclusions: The results emphasize the primary importance of snow-inducedchanges in length of growing season on carbon uptake in alpinetemperate meadows. It was also demonstrated how using leaf-traitvalues of the dominants is a useful approach for modelling ecosystemcarbon-cycle-related processes, particularly when continuousmeasurements of CO₂ fluxes are technically difficult. The studythus represents an important step in addressing the challengeof using a plant functional-trait approach for biogeochemicalmodelling.     

Plant competition for light analyzed with a multispecies canopy model

Summary Competition for light among species in a mixed canopy can be assessed quantitatively by a simulation model which evaluates the importance of different morphological and photosynthetic characteristics of each species. A model was developed that simulates how the foliage of all species attenuate radiation in the canopy and how much radiation is received by foliage of each species. The model can account for different kinds of foliage (leaf blades, stems, etc.) for each species. The photosynthesis and transpiration for sunlit and shaded foliage of each species is also computed for different layers in the canopy. The model is an extension of previously described single-species canopy photosynthesis simulation models. Model predictions of the fraction of foliage sunlit and interception of light by sunlit and shaded foliage for monoculture and mixed canopies of wheat (Triticum aestivum) and wild oat (Avena fatua) in the field compared very well with measured values. The model was used to calculate light interception and canopy photosynthesis for both species of wheat/wild oat mixtures grown under normal solar and enhanced ultraviolet-B (290–320 nm) radiation (UV-B) in a glasshouse experiment with no root competition. In these experiments, measurements showed that the mixtures receiving enhanced UV-B radiation had a greater proportion of the total foliage area composed of wheat compared to mixtures in the control treatments. The difference in species foliage area and its position in the canopy resulted in a calculated increase in the portion of total canopy radiation interception and photosynthesis by wheat. This, in turn, is consistent with greater canopy biomass of wheat reported in canopies irradiated with supplemental UV-B.     

UV-B and PAR in single and mixed canopies grown under different UV-B exclusions in the field

The purpose of this study was to investigate whether differences in canopy architecture due to the investigated species (planophile versus erectophile, single versus mixed canopies) or to UV-B effects on plant morphology, lead to differences in UV-B and UV-B/PAR doses within canopies.The development of a very small (10 mm diameter) UV-B and PAR sensor on a long 5 mm wide stick allowed us to measure the penetration of UV-B and PAR in single and mixed canopies of the grass Dactylis glomerata and white clover, Trifolium repens. The plants were grown in greenhouses covered with different thicknesses (3 and 5 mm) of UV-transmittant plexi (12 and 18% UV-B exclusion).For clover, a planophile vegetation, radiation penetration was very low for both UV-B and PAR. UV-B penetration was much less than for PAR, resulting in low UV-B/PAR ratio's within the canopy. This is explained by the low UV-B transmittance of the leaves (<0.1 %) in combination with the planophile leaves.In the grass species, both UV-B and PAR penetrated much deeper into the canopy due to the erectophile structure. The difference between UV-B and PAR penetration was generally quite small except in very tall canopies.The mixed species canopies showed results comparable to the clover canopies. Due to the strongly increased grass growth in these plots, light penetration was generally much lower than in the single species cultures. The increased growth of grass in these mixed plots could be linked to the lower UV-B/PAR dose they received.In plots grown under the higher UV-B level there was a relative decrease in UV-B/PAR ratio within the canopy for both species, compared to canopies from the lower UV-B greenhouses. This could not be explained by changes in leaf angle or biomass, but might be linked to the increase in leaf transmittance of PAR.     

Cessation of tillering in spring wheat in relation to light interception and red : far-red ratio

BACKGROUND AND AIMS: The production of axillary shoots (tillering) in spring wheat (Triticum aestivum) depends on intraspecific competition. The mechanisms that underlie this competition are complex, but light within the wheat canopy plays a key role. The main objectives of this paper are to analyse the effects of plant population density and shade on tillering dynamics of spring wheat, to assess the canopy conditions quantitatively at the time of tillering cessation, and to analyse the relationship between the tiller bud and the leaf on the same phytomer. METHODS: Spring wheat plants were grown at three plant population densities and under two light regimes (25 % and 100 % light). Tiller appearance, fraction of the light intercepted, and red : far-red ratio at soil level were recorded. On six sampling dates the growth status of axillary buds was analysed. KEY RESULTS: Tillering ceased earlier at high population densities and ceased earlier in the shade than in full sunlight. At cessation of tillering, both the fraction of light intercepted and the red : far-red ratio at soil level were similar in all treatments. Leaves on the same phytomer of buds that grew out showed more leaf mass per unit area than those on the same phytomer of buds that remained dormant. CONCLUSIONS: Tillering ceases at specific light conditions within the wheat canopy, independent of population density, and to a lesser extent independent of light intensity. It is suggested that cessation of tillering is induced when the fraction of PAR intercepted by the canopy exceeds a specific threshold (0.40-0.45) and red : far-red ratio drops below 0.35-0.40.     

Plant light interception can be explained via computed tomography scanning: demonstration with pyramidal cedar (Thuja occidentalis, Fastigiata)

BACKGROUND AND AIMS: Light interception by the leaf canopy is a key aspect of plant photosynthesis, which helps mitigate the greenhouse effect via atmospheric CO(2) recycling. The relationship between plant light interception and leaf area was traditionally modelled with the Beer-Lambert law, until the spatial distribution of leaves was incorporated through the fractal dimension of leafless plant structure photographed from the side allowing maximum appearance of branches and petioles. However, photographs of leafless plants are two-dimensional projections of three-dimensional structures, and sampled plants were cut at the stem base before leaf blades were detached manually, so canopy development could not be followed for individual plants. Therefore, a new measurement and modelling approach were developed to explain plant light interception more completely and precisely, based on appropriate processing of computed tomography (CT) scanning data collected for developing canopies. METHODS: Three-dimensional images of canopies were constructed from CT scanning data. Leaf volumes (LV) were evaluated from complete canopy images, and fractal dimensions (FD) were estimated from skeletonized leafless images. The experimental plant species is pyramidal cedar (Thuja occidentalis, Fastigiata). KEY RESULTS: The three-dimensional version of the Beer-Lambert law based on FD alone provided a much better explanation of plant light interception (R(2) = 0.858) than those using the product LV*FD (0.589) or LV alone (0.548). While values of all three regressors were found to increase over time, FD in the Beer-Lambert law followed the increase in light interception the most closely. The delayed increase of LV reflected the appearance of new leaves only after branches had lengthened and ramified. CONCLUSIONS: The very strong correlation obtained with FD demonstrates that CT scanning data contain fundamental information about the canopy architecture geometry. The model can be used to identify crops and plantation trees with improved light interception and productivity.     

Modelling photo-modulated internode elongation in growing glasshouse cucumber canopies

? Growing glasshouse plant canopies are exposed to natural fluctuations in light quantity, and the dynamically changing canopy architecture induces local variations in light quality. This modelling study aimed to analyse the importance of both light signals for an accurate prediction of individual internode lengths. ? We conceptualized two model approaches for estimating final internode lengths (FILs). The first one is only photosynthetically active radiation (PAR)-sensitive and ignores canopy architecture, whereas the second approach uses a functional-structural growth model for considering variations in both PAR and red : far-red (R : FR) ratio (L-Cucumber). Internode lengths measured in three experiments were used for model parameterization and evaluation. ? The overall trends for the simulated FILs using the exclusively PAR-sensitive model approach were already in line with the measured FILs, but they underestimated FILs at higher ranks. L-Cucumber provided considerably better FIL predictions under various light conditions and canopy architectures. ? Both light signals are needed for an accurate estimation of the FILs, and only L-Cucumber is able to consider R : FR signals from the growing canopy. Yet this study highlights the significance of the PAR signal for predicting FILs as neighbour effects increase, which indicates a potential role of photosynthate signalling in internode elongation.     

3D Architectural Modelling of Aerial Photomorphogenesis in White Clover (Trifolium repens L.) using L-systems

The objective of this work was to construct a model of aerialdevelopment of clover that takes into account morphogeneticresponses to the light environment, and to use it to analyseand understand these processes in terms of signal perceptionand integration. The plant model was interfaced with a MonteCarlo model that determines photosynthetically active radiation(PAR) and red/far-red ratio (R/FR) throughout the canopy, takinginto account the absorption, reflection and transmission oflight by individual leaves. Light intensity and quality weresensed by the plant model at discrete time intervals and atdiscrete sites of perception: apices, emerging internodes andpetiole tips. This input regulated the final size of internodesand leaves, the vertical positioning of leaves, and the branchingdelay. The empirical relations (regression functions) quantifyingthis regulation were derived from data reported in the literatureand original measurements. Simulations produced realistic visualizationsand quantitative characterizations of the modelled plants fordifferent light treatments. These results were in general agreementwith observations of real plants growing under similar conditions,suggesting that the dependence of organ size and position onlight treatments can be regarded as an integration of the responsesof individual plant organs to their local light environment.The model is used to describe the regulation of branch appearanceand the impact of self-shading on plant morphogenesis as a functionof local light environment. Copyright 2000 Annals of BotanyCompany Clover, Trifolium repens L, photomorphogenesis, plant architecture, L-system, modelling, Monte-Carlo method, competition for light, red : far-red ratio, irradiance, light quality, leaf size, self-shading     

Molecular analysis of natural leaf senescence in Arabidopsis thaliana

Using artificial canopies, several authors have shown that horizontally propagated and overall propagated radiation beneath the canopy differ substantially in spectral distribution in the red (R) and far red (FR) wavelengths. Given the lack of information about light quality under real crop canopies, the R:FR ratio of vertical and horizontal radiation beneath field-grown maize, soybean and wheat was monitored until leaf area index (LAI) reached 4, 2.5 and 6.9, respectively.
A Li-Cor 1800 spectroradiometer with a remote cosine receptor fitted with a quartz fibre-optic light-guide was used. To isolate radiation coming from a given direction, a black coated tube was fitted to the cosine receptor. The viewing angle was 15°. In open conditions, the values of R:FR from the upper hemisphere were between 1.07 and 1.20. For vertically and horizontally-propagated light, average values were 1.22 and 0.75 respectively.
Beneath the canopy, both R:FR and photosynthetic photon flux density (PPFD) from the entire upper hemisphere decreased in relation to LAI and crop height. R:FR of the horizontal component were found to be generally much lower than the vertical, which decreased significantly only in the later measurements.
The lowest R:FR values were recorded under wheat and soybean canopies. Even the very low LAIs present at early development stages were enough to cause a sharp decrease of R:FR in the horizontal fluxes. Referring to the entire upper hemisphere, PPFD transmittance and R:FR as a percentage of the external references appeared well correlated.     

Structure is more important than physiology for estimating intracanopy distributions of leaf temperatures

Estimating leaf temperature distributions (LTDs) in canopies is crucial in forest ecology. Leaf temperature affects the exchange of heat, water, and gases, and it alters the performance of leaf‐dwelling species such as arthropods, including pests and invaders. LTDs provide spatial variation that may allow arthropods to thermoregulate in the face of long‐term changes in mean temperature or incidence of extreme temperatures. Yet, recording LTDs for entire canopies remains challenging. Here, we use an energy‐exchange model (RATP) to examine the relative roles of climatic, structural, and physiological factors in influencing three‐dimensional LTDs in tree canopies. A Morris sensitivity analysis of 13 parameters showed, not surprisingly, that climatic factors had the greatest overall effect on LTDs. In addition, however, structural parameters had greater effects on LTDs than did leaf physiological parameters. Our results suggest that it is possible to infer forest canopy LTDs from the LTDs measured or simulated just at the surface of the canopy cover over a reasonable range of parameter values. This conclusion suggests that remote sensing data can be used to estimate 3D patterns of temperature variation from 2D images of vegetation surface temperatures. Synthesis and applications. Estimating the effects of LTDs on natural plant–insect communities will require extending canopy models beyond their current focus on individual species or crops. These models, however, contain many parameters, and applying the models to new species or to mixed natural canopies depends on identifying the parameters that matter most. Our results suggest that canopy structural parameters are more important determinants of LTDs than are the physiological parameters that tend to receive the most empirical attention.     

Do Variations in Local Leaf Irradiance Explain Changes to Leaf Nitrogen within Row Maize Canopies?

Numerous studies have dealt with the relationship between leafnitrogen content and leaf irradiance. However, most of themrefer to dense stands presenting reduced horizontal heterogeneityof foliage distribution. Both gradients of leaf nitrogen andleaf irradiance related to canopy depth are significant undersuch conditions, and modelling radiative exchange using a turbid-mediumanalogy and dividing the canopy into vegetation layers is sufficient.Conversely, row crops such as maize are characterized by stronghorizontal heterogeneity of foliage distribution and the one-dimensional(1D) approach may be unsuitable. We thus modelled the three-dimensional(3D) geometry of maize canopies with varying densities and atdifferent developmental stages using plant digitizing underfield conditions. The nitrogen content per unit area of eachleaf part was obtained subsequently by nitrogen analysis. Wenext calculated radiative exchange using a 3D volume-based approachwithin the canopies in order to estimate local leaf irradianceon a daily integration scale. Vertical gradients in leaf nitrogencontent per unit area observed in dense stands during the vegetativephase corresponded largely to those reported in the literature.We also identified significant gradients in nitrogen contentalong the leaves, which had not before been clearly demonstrated.Our study shows that local light climate during plant developmentplays a major role in leaf nitrogen distribution and remobilization.Moreover, brutal plant thinning involves rapid changes in leafnitrogen partitioning. It is concluded that taking account ofthe 3D heterogeneity of nitrogen and irradiance distributionmay have implications for modelling crop photosynthesis andproduction. Copyright 1999 Annals of Botany Company 3D plant architecture, horizontal gradients in leaf nitrogen, leaf irradiance, leaf nitrogen content per unit area, maize, nitrogen partitioning, nitrogen remobilization, virtual plant, Zea mays L.     

Relationships between canopy complexity and germination microsites for Phalaris arundinacea L.

Microsites that prevent seed germination are critical for slowing the invasion of native plant communities by aggressive, clonal species. A suitable model for study is the clonal grass, Phalaris arundinacea, which reproduces prolifically from seed and is spreading into wetlands across temperate North America. Knowing that light conditions control its seed germination in the laboratory and that light varies with canopy complexity in a Wisconsin fen, we tested multiple attributes of microsites under spatially and temporally dynamic canopies (namely, presence/absence of a matrix species, number of species in the canopy, plus indirect effects of three soil water levels) for their control of germination in microcosms. Our 6-species canopies + the matrix of Glyceria striata had the densest cover and reduced P. arundinacea germination to 1.9%, compared to 7.3% for 1-species canopies + the matrix. After selectively removing canopy components, germination increased to 36.1% for 6-species and 33.0% for 1-species canopies. Comparing canopies with each of the six species, germination declined in relation to increasing leaf width. Given moist soil, P. arundinacea germination microsites are determined by canopy complexity, which affects light penetration, which in turn determines germination rate.     

水稻冠层结构变化对二向反射率的影响

通过对植被二向反射特性的研究,可反演植被冠层结构信息,如叶面积指数、平均叶角、株高、覆盖率等。在大田晚稻（秀水63）移栽后第26、35、41、49、62、67和86d,对水稻冠层结构及二向反射率进行实测,并分析了二向反射率随冠层结构变化规律,结果表明,植被冠层二向反射率对入射角与观测角的敏感性随着植被冠层结构的变化而变化,蕴涵着丰富的植被结构信息。     

The effect of grasses on the quality of transmitted radiation and its influence on the growth of white clover Trifolium repens

Summary Plants of white clover Trifolium repens were grown under the canopies of three grass species, Lolium perenne, Agrostis tenuis and Holcus lanatus, and under simulated canopies of black polythene and controls were exposed to unfiltered natural radiation. The canopies were adjusted so that they transmitted equal intensities of Photosynthetically Active Radiation (P.A.R.). The ratio of red to far red radiation () was unchanged under the black polythene canopies but was reduced under canopies of Lolium and Agrostis and even more so under Holcus. The effect of canopy filtered radiation on the growth of clover was greatly to reduced internode length, mean number of nodes, the number of branched nodes and the number of rooted nodes and greatly to increase petiole length. The effect of canopies of Holcus was greater than that of the other grass species both in its effect on and on the responses of the clover plant to its shade.     

Foliage randomness and light interception in 3-D digitized trees: an analysis from multiscale discretization of the canopy

Light models for vegetation canopies based on the turbid medium analogy are usually limited by the basic assumption of random foliage dispersion in the canopy space. The objective of this paper was to assess the effect of three possible sources of non-randomness in tree canopies on light interception properties. For this purpose, four three-dimensional (3-D) digitized trees and four theoretical canopies – one random and three built from fractal rules – were used to compute canopy structure parameters and light interception, namely the sky-vault averaged STAR (Silhouette to Total Area Ratio). STAR values were computed from (1) images of the 3-D plants, and (2) from a 3-D turbid medium model using space discretization at different scales. For all trees, departure from randomness was mainly due to the spatial variations in leaf area density within the canopy volume. Indeed STAR estimations, based on turbid medium assumption, using the finest space discretization were very close to STAR values computed from the plant images. At this finest scale, foliage dispersion was slightly clumped, except one theoretical fractal canopy, which showed a marked regular dispersion. Taking into account a non-infinitely small leaf size, whose effect is theoretically to shorten self-shading, had a minor effect on STAR computations. STAR values computed from the 3-D turbid medium were very sensitive to plant lacunarity, a parameter introduced in the context of fractal studies to characterize the distribution of gaps in porous media at different scales. This study shows that 3-D turbid medium models based on space discretization are able to give correct estimation of light interception by 3-D isolated trees, provided that the 3-D grid is properly defined, that is, discretization maximizes plant lacunarity.     

Tree seedling canopy responses to conflicting photosensory cues

Light with decreased red:far-red (R:FR) ratios may signal neighbor presence and trigger plant developmental responses. There is some evidence that plant canopies forage towards increased R:FR ratios, but it is unclear to what extent R:FR versus the total amount of photosynthetically active radiation (PAR) influences canopy foraging responses among forest trees. The objective of this study was to examine the relative importance of PAR and R:FR as photosensory cues leading to tree canopy foraging responses. Seedlings of Betula papyrifera Marshall (paper birch) were grown in an experimental garden. Each seedling was germinated and grown in its own shading structure and exposed to two spatially separated light environments, in a factorial design of PAR and R:FR. Plant canopy foraging was evaluated at the end of one growing season in terms of canopy displacement, canopy area, leaf number, direction of stem lean, petiole aspect, and lamina aspect with respect to experimental light treatments. Leaf number and canopy area were greater on the high PAR sides of plants, irrespective of the R:FR treatment. Seedling canopies were displaced towards the direction of high PAR, but this relationship was not significant across all treatments. Petiole aspect was random and showed no significant directedness towards any of the light treatments. Lamina aspect and the direction of stem lean were distributed towards the direction of high PAR, irrespective of the R:FR treatment. Overall, first-year B. papyrifera seedlings used PAR, rather than R:FR ratio, as a photosensory cue for canopy light foraging.     

Sun‐induced chlorophyll fluorescence from high‐resolution imaging spectroscopy data to quantify spatio‐temporal patterns of photosynthetic function in crop canopies

Passive detection of sun‐induced chlorophyll fluorescence (SIF) using spectroscopy has been proposed as a proxy to quantify changes in photochemical efficiency at canopy level under natural light conditions. In this study, we explored the use of imaging spectroscopy to quantify spatio‐temporal dynamics of SIF within crop canopies and its sensitivity to track patterns of photosynthetic activity originating from the interaction between vegetation structure and incoming radiation as well as variations in plant function. SIF was retrieved using the Fraunhofer Line Depth (FLD) principle from imaging spectroscopy data acquired at different time scales a few metres above several crop canopies growing under natural illumination. We report the first maps of canopy SIF in high spatial resolution. Changes of SIF were monitored at different time scales ranging from quick variations under induced stress conditions to seasonal dynamics. Natural changes were primarily determined by varying levels and distribution of photosynthetic active radiation (PAR). However, this relationship changed throughout the day demonstrating an additional physiological component modulating spatio‐temporal patterns of SIF emission. We successfully used detailed SIF maps to track changes in the canopy's photochemical activity under field conditions, providing a new tool to evaluate complex patterns of photosynthesis within the canopy.