Scaling up Semi-Arid Grassland Biochemical Content from the Leaf to the Canopy Level: Challenges and Opportunities

Remote sensing imagery is being used intensively to estimate the biochemical content of vegetation (e.g., chlorophyll, nitrogen, and lignin) at the leaf level. As a result of our need for vegetation biochemical information and our increasing ability to obtain canopy spectral data, a few techniques have been explored to scale leaf-level biochemical content to the canopy level for forests and crops. However, due to the contribution of non-green materials (i.e., standing dead litter, rock, and bare soil) from canopy spectra in semi-arid grasslands, it is difficult to obtain information about grassland biochemical content from remote sensing data at the canopy level. This paper summarizes available methods used to scale biochemical information from the leaf level to the canopy level and groups these methods into three categories: direct extrapolation, canopy-integrated approach, and inversion of physical models. As for semi-arid heterogeneous grasslands, we conclude that all methods are useful, but none are ideal. It is recommended that future research should explore a systematic upscaling framework which combines spatial pattern analysis, canopy-integrated approach, and modeling methods to retrieve vegetation biochemical content at the canopy level

A physiological Plant Growth Simulation Engine Based on Accurate Radiant Energy Transfer

We present a new model for plant growth simulation, taking into account the eco-physiological processes driving plant development with unprecedented fidelity. The growth model, based on a physiological analysis, essentially simulates the internal function of the plant, and has been validated against measured biological data with excellent results. We show how to account for the influence of light through photosynthesis, and thereby incorporate the effects of a given plant's immediate environment on its architecture, shape and size. Since biological matter is controlled by water transpiration and received radiant enery, the model requires efficient and accurate simulation of radiant energy exchanges. We describe a complete lighting simulation system tailored for the difficult case of plants, by adapting state-of-the-art techniques such as hierarchical instanciation for radiosity and general BRDF modeling. Our results show that (a) our lighting simulation system efficiently provides the required information at the desired level of accuracy, and (b) the plant growth model is extremely well calibrated against real plants and (c) the combined system can simulate many interesting growth situations with direct feedback from the environment on the plant's characteristics. Applications range from landscape simulation to agronomical and agricultural studies, and to the design of virtual plants responding to their environment

온실 내 군락 내부 LED보광에 의한 파프리카의 광 이용 효율 및 물 이용 효율 평가

학위논문(석사) -- 서울대학교대학원 : 농업생명과학대학 농림생물자원학부, 2021.8. 권성민.In greenhouses, the higher plant density, the less sunlight inside the canopy due to mutual shadings by adjacent plants. As a countermeasure, inter-lighting has been introduced to compensate for the lack of light in the middle and bottom parts of the canopy. However, most research have focused on growth and yield, not light use efficiency (LUE) and water use efficiency (WUE). The objective of this study was to evaluate the LUE and WUE of sweet peppers subjected to inter-lighting in greenhouses. Two lighting treatments, natural light (control) and supplemental inter-lighting of red and blue LEDs, were applied. The inter-lighting started at 34 days after transplanting (DAT). The ratio of red and blue light in photosynthetic photon flux density (PPFD) was 8:2, and the total PPFD was adjusted to 71 μmol·m2·s1 at 20 cm distance. To quantify the transpiration from the plants, the amount of daily transpiration was measured by subtracting the drainage from the supplied nutrient solution, and hydroponic system weight change. The photosynthetic rate was obtained by measuring light response curves at light intensities of 0, 50, 100, 200, 400, 600, 900, 1200, 1500, and 2000 μmol·m2·s1 in PPFD. The LUEs were calculated based on the light interception obtained by 3D-scanned plant models and ray-tracing simulation. The WUEs were calculated using dry weight per accumulated water consumption. The calculated results showed the increase in LUE at the canopy level, which is likely due to the improvement of canopy light distribution by inter-lighting. The WUE for biomass and fruit yield were higher in inter-lighting than those in the control. These results were due to the increases in plant dry weight and fruit yield, which is greater than the increase in water consumption by inter-lighting. In this study, the improvement of LUE and WUE by inter-lighting could be quantified by optical simulation and the water consumption during the whole growth period.온실에서는 재식밀도가 높아질수록 인접한 식물간의 간섭 현상으로 캐노피 내부에 빛이 부족하게 된다. 이에 대한 대책으로 군락 중, 하단부의 빛 부족을 보완하기 위해 군락 내 보광을 도입하고 있다. 현재 대부분의 연구는 광이용 효율(LUE), 물이용 효율(WUE)이 아닌 생장과 수확량에 초점을 맞추어 왔다. 따라서 이 연구의 목적은 온실에서 군락 내 측면 보광(inter-lighting) 하에서 자란 파프리카의 LUE와 WUE를 평가하는 것이다. 자연광(대조구)과 자연광에 적색 및 청색 LED에 의한 보광 처리구가 적용되었다. 보광 처리는 정식 후 34일 (DAT)에 시작하였고, 적색 및 청색 LED 비율이 8:2인 광원은 20cm 거리에서 71mol · m-2 · s-1로 설정하였다. 식물의 증산량을 정량화 하기 위해 수경재배 무게측정 시스템으로 급액량에서 배액량을 제하여 하루 증산량을 측정했다. 광합성속도는 0, 50, 100, 200, 400, 600, 900, 1200, 1500, 2000 μmol · m-2 · s-1에서 광반응 곡선을 측정하여 얻었다. LUE는 40, 60, 80, 100 및 120 DAT에서 3D 식물 모델 및 광학 시뮬레이션으로 측정한 수광 태세를 기반으로 계산하였다. WUE는 40, 60, 80, 100 및 120 DAT에서 누적된 물 소비량 대비 건조중으로 계산하였다. 시뮬레이션 결과에서 캐노피 수준의 LUE가 증가하였는데, 이는 보광 이 캐노피 내부의 수광 개선에 기인한 것으로 보인다. 건물중 및 과일 생산량에 대한 WUE는 대조군보다 보광 처리구에서 더 높았다. 이러한 결과는 보광에 의한 물 소비보다 식물의 건조 중량과 과일 수확량의 증가폭이 더 높았기 때문이다. 본 연구에서는 광학 시뮬레이션과 전체 생장 기간 동안의 물 이용량을 분석하여 군락 내 측면 보광으로 인한 LUE 및 WUE 증가를 정량화 할 수 있게 되었다.INTRODUCTION 1 LITERATURE REVIEW 3 MATERIALS AND METHODS 5 RESULTS 15 DISCUSSION 25 CONCLUSION 28 LITERATURE CITED 29 ABSTRACT IN KOREAN 39석

Modelling and remote sensing of canopy light interception and plant stress in greenhouses

A greenhouse crop can be approached as an open system that can be affected by a number of parameters such as light, climate or nutrient supply. In the last decades efforts have been made to understand the functioning of this system and the interaction between the different parameters. The intensive nature of greenhouse cultivation combined with the economic necessity to enlarge the farm size makes the development of decision support systems (DSS) imperative to help the growers in managing their farms efficiently. The foundation of DSS are plant models and in order to work more efficiently they should be able to receive information in real time from sensors that measure different plant parameters such as light interception, leaf area index and photosynthetic stress in a non-destructive way. In order to develop functional DSS it is imperative to develop accurate models and monitoring techniques applied in the specific greenhouse environment. The aim of this thesis was to explore different techniques to simulate and monitor light interception and photosynthesis by a greenhouse grown tomato canopy. Since photosynthesis is directly linked to light absorption we opted to develop a three dimensional model that takes into account the explicit plant architecture. Different methodologies to monitor these physiological properties online by means of remote sensing were also explored. A number of physiological tomato models have been proposed the last decades, their main challenge being the correct simulation of fruit yield. For this, an accurate simulation of light interception, and thus photosynthesis, is of primary importance. 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. In Chapter 2.1 the first steps towards the development of the model are presented. Light interception is highly dependent on the canopy structure, which is affected, among others, by the distance between plant rows, the distance of plants within the row, leaf pruning and crop variety. The model was used to test different crop planting scenarios on their effect on light interception. Light interception from the planting scenarios was then compared with results of a totally homogeneous canopy. Also analysis of differences between manual measurements of leaf length, width, elevation angle and leaf orientation was conducted. Changes of leaf elevation angles at two different times of the day were also measured. In tomato differences in leaf length, width and elevation angle of the leaves were mainly observed in the upper 90cm of the plant, in the still developing zone. Changes of the architectural characteristics of structural plant characteristics affected directly light interception by the crop canopy. Nevertheless even if plant structure stayed the same, light penetration could easily be manipulated by changing the row spacing in the crop, thus affecting light interception and potentially plant production. In Chapter 2.2 the development and calibration of a functional-structural tomato model is fully described. The model was used to investigate the 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. The model consists of an architectural static virtual plant coupled with a nested radiosity model for light absorption and a leaf photosynthesis module. Different scenarios for horizontal and vertical distributions of light interception, incident light and photosynthesis were investigated under diffuse and direct light conditions. Simulated light interception showed a good correspondence to the measured values. Explicitly described leaf elevation angles resulted in higher light interception in the middle of the plant canopy compared to fixed and ellipsoidal leaf elevation 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 an east-west orientation by 10% in 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 ca. 8% increase on simulated canopy photosynthesis. Manipulation of plant structure can strongly affect light distribution in the canopy and photosynthesis. In Chapter 2.3 the idea of identifying different plant ideotypes for optimization of light absorption and photosynthesis was explored. Using the functional-structural tomato model presented in the previous chapters, a range of different plant architectural characteristics were tested for two different seasons in order to find the optimal architecture with respect to light absorption and photosynthesis. Sensitivity analyses were carried out for leaf elevation angle, leaf phyllotaxis, leaflet angle, leaf shape, leaflet arrangement and internode length. From the results of this analysis two possible ideotypes were proposed. Increasing light absorption in the top part of the canopy by 25 %, without changing light absorption of the canopy as a whole, augmented photosynthesis by 6 % in winter and decreased it by 7 % in summer. The measured plant structure was already optimal with respect to leaf elevation angle, leaflet angle and leaflet arrangement for both light absorption and photosynthesis while phyllotaxis had no effect. Increasing the length-to-width ratio of leaves by 1.5 or increasing internode length from 7 to 12 cm led to an increase of 7 – 10 % for light absorption and photosynthesis. The most important architectural traits found were the internode length and the leaf shape as they affect vertical light distribution in the canopy distinctly. A new plant ideotype with more spacious canopy architecture due to long internodes and long and narrow leaves led to an increase in photosynthesis of up to 10 %. In Chapter 3.1 ways to monitor on-line LAI and PAR interception of the canopy, under greenhouse conditions, through reflectance measurements, were explored. LAI and PAR interception were measured at the same moments as reflectance at six wavelengths in different developmental stages of tomato and sweet pepper plants. Normalized Difference Vegetation Index (NDVI) was calculated. Relationships between the measured parameters were established in experimental greenhouses and subsequently these were tested in commercial greenhouses. The best estimation for LAI and PAR interception was obtained from reflectance at 460nm for both tomato and sweet pepper. The goodness of the fit was validated with data from the commercial greenhouses and was also tested in this study. The divergence of the results from the ones reported from field experiments can be traced back to the special greenhouse environment, where more sources of reflectance are added due to construction parts and a white plastic covered background. Reflectance measurements offer a non- destructive way to estimate PAR interception and LAI (up to the value of 3) in greenhouse production systems. The relationship established between reflectance at 460 nm, PAR interception and LAI for both tomato and sweet pepper, can become a good tool for crop online monitoring in greenhouse conditions. Furthermore if information from reflectance sensors is used as input directly into the crop models, new opportunities for decision support systems in greenhouse production could be opened up. Photosynthetic stress induced by water deprivation in plants affects a number of physiological processes such as photosynthetic rate, stomatal conductance as well as the operating efficiency of PSII and non- photochemical quenching. Photochemical Reflectance Index (PRI) is reported to be sensitive to changes of xanthophyll cycle that occur during stress and could possibly be used to monitor changes in the physiological parameters mentioned before. In Chapter 3.2 the use of PRI as an early photosynthetic stress indicator was evaluated. A water stress treatment was imposed on a greenhouse tomato crop. CO2 assimilation, stomatal conductance, light and dark adapted fluorescence as well as PRI and relative water content of the rooting medium RWCs% where repeatedly measured. The same measurements were also performed on well-irrigated plants that acted as a reference. The experiment was repeated in four consecutive weeks. Results showed that PRI can be used as an early stress indicator only when light intensity at crop level was above 700μmol m-2 s-1. At lower values of light intensity the relationship of PRI to RWCs% was poor in comparison to photosynthesis or fluorescence parameters that showed a high correlation to RWCs%. For that reason we can conclude that PRI as water stress indicator cannot be independent of the ambient light conditions and its use can make sense only under conditions of high light. Finally in Chapter 4 the main achievements and limitations of this study are discussed and directions for future research are proposed. </p

Optimal Design of Plant Canopy Based on Light Interception: A Case Study With Loquat

Canopy architecture determines the light distribution and light interception in the canopy. Reasonable shaping and pruning can optimize tree structure; maximize the utilization of land, space and light energy; and lay the foundation for achieving early fruiting, high yield, health and longevity. Due to the complexity of loquat canopy architecture and the multi-year period of tree growth, the variables needed for experiments in canopy type training are hardly accessible through field measurements. In this paper, we concentrated on exploring the relationship between branching angle and light interception using a three-dimensional (3D) canopy model in loquat (Eriobotrya japonica Lindl). First, detailed 3D models of loquat trees were built by integrating branch and organ models. Second, the morphological models of different loquat trees were constructed by interactive editing. Third, the 3D individual-tree modeling software LSTree integrated with the OpenGL shadow technique, a radiosity model and a modified rectangular hyperbola model was used to calculate the silhouette to total area ratio, the distribution of photosynthetically active radiation within canopies and the net photosynthetic rate, respectively. Finally, the influence of loquat tree organ organization on the light interception of the trees was analyzed with different parameters. If the single branch angle between the level 2 scaffold branch and trunk is approximately 15° and the angles among the level 2 scaffold branches range from 60 to 90°, then a better light distribution can be obtained. The results showed that the branching angle has a significant impact on light interception, which is useful for grower manipulation of trees, e.g., shoot bending (scaffold branch angle). Based on this conclusion, a reasonable tree structure was selected for intercepting light. This quantitative simulation and analytical method provides a new digital and visual method that can aid in the design of tree architecture

A functional–structural plant model that simulates whole- canopy gas exchange of grapevine plants (Vitis vinifera L.) under different training systems

Background and Aims: Scaling from single-leaf to whole-canopy photosynthesis faces several complexities related to variations in light interception and leaf properties. To evaluate the impact of canopy strucuture on gas exchange, we developed a functional–structural plant model to upscale leaf processes to the whole canopy based on leaf N content. The model integrates different models that calculate intercepted radiation, leaf traits and gas exchange for each leaf in the canopy. Our main objectives were (1) to introduce the gas exchange model developed at the plant level by integrating the leaf-level responses related to canopy structure, (2) to test the model against an independent canopy gas exchange dataset recorded on different plant architectures, and (3) to quantify the impact of intra-canopy N distribution on crop photosynthesis. Methods: The model combined a 3D reconstruction of grapevine (Vitis vinifera) canopy architecture, a light interception model, and a coupled photosynthesis and stomatal conductance model that considers light-driven variations in N distribution. A portable chamber device was constructed to measure whole-plant gas exchange to validate the model outputs with data collected on different training systems. Finally, a sensitivity analysis was performed to evaluate the impact on C assimilation of different N content distributions within the canopy. Key Results: By considering a non-uniform leaf N distribution within the canopy, our model accurately reproduced the daily pattern of gas exchange of different canopy architectures. The gain in photosynthesis permitted by the non-uniform compared with a theoretical uniform N distribution was about 18 %, thereby contributing to the maximization of C assimilation. By contrast, considering a maximal N content for all leaves in the canopy overestimated net CO2 exchange by 28 % when compared with the non-uniform distribution. Conclusions: The model reproduced the gas exchange of plants under different training systems with a low error (10 %). It appears to be a reliable tool to evaluate the impact of a grapevine training system on water use efficiency at the plant level.EEA MendozaFil: Prieto, Jorge Alejandro. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Mendoza; Argentina.Fil: Louarn, Gaëtan. Institut National de la Recherche Agronomique; FranciaFil: Perez Peña, Jorge Esteban. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Mendoza; ArgentinaFil: Ojeda, Hernan. Institut National de la Recherche Agronomique. Unité expérimentale de Pech Rouge; FranciaFil: Simonneau, Thierry. Institut National de la Recherche Agronomique. LEPSE Montpellier; FranciaFil: Lebon, Eric. Institut National de la Recherche Agronomique. Unité Mixte de Recherche; Franci

Influence of canopy structure on light interception and productivity of greenhouse cucumber

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