Functional control of nitrogen distribution in heterogeneous plant canopies
Final Report Abstract
Acclimation of leaf photosynthetic traits to fluctuating environments is a key mechanism to maximize crop fitness. Constant tracking of light environments is crucial for efficient use of limiting resources like nitrogen (N), especially for species with continuously leaf-forming nature, such as greenhouse cucumber (Cucumis sativus L.). The purpose of this project was to develop an integrated understanding of (1) the light acclimation of photosynthetic N in both intra-leaf partitioning between functions and intra-plant distribution between leaves, and (2) the genotypic variations of light acclimation. To achieve this, we applied a modelling approach to identify the optimal photosynthesis N distribution and partitioning which maximized whole plant carbon assimilation under various scenarios of incident light levels, N supply levels, and plant densities. The model framework combined the FvCB photosynthesis model and dynamics canopy architecture model of cucumber described by a multilayer model (MLM) and a 3D functional-structural model (FSM). To capture the influences of light and N supply on the key parameters in the photosynthesis model, we proposed a photosynthetic protein turnover model, which was parameterized using data obtained under controlled environments and evaluated using data obtained in the greenhouse. Two cucumber varieties were examined, Aramon and SC-50, which were bred under contrast cultural systems, greenhouse vertical single-stem and field creeping multi-branch canopy, respectively. The light dependency of protein synthesis was able to explain the photosynthetic acclimatory response to fluctuating light, and to predict canopy photosynthesis with comparable accuracy using either the MLM or the FSM. The present model is a novel approach to quantify different components in the photosynthetic machinery as a dynamic process. The analyses indicated that both between-leaf photosynthetic N distribution and between-function photosynthetic N partitioning were optimal in Aramon simulated under the average light level during plant growth (aDPI). However, light levels diverged from aDPI could result in sub-optimum. For example, under 200% aDPI, limited acropetal photosynthetic N reallocation was predicted to cause up to 7% loss of daily plant carbon assimilation in plants grown under low N supply (2.5 mM) in comparison with the theoretical optimal distribution. On the other hand, by reinvesting N into the limiting function, up to 25% increase in daily plant carbon assimilation was expected. It was interesting to note that SC-50 had less photosynthetic N in leaves than Aramon but a more efficient partitioning strategy. These results highlight the differences in the light acclimation strategies between varieties. It also indicated that more insights could be obtained by applying our approach to other plant species with contrasting canopy structure or phenology. The proposed modelling framework provides an interpretation for acclimatory mechanisms under fluctuating light, and enables in silico manipulations and tests of photosynthetic acclimation in heterogeneous canopies. Further studies using this approach in other varieties or species would improve our understanding in physiological limits due to fluctuating light environment. For example, it may help in defining target traits of a crop species to be improved by breeder or in designing cropping systems (e.g., training system and inter-lighting) for higher N use efficiency.
Publications
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2018. Modelling dynamic photosynthetic acclimation based on nitrogen turnover under different photoperiods. Mitteilung der Gesellschaft für Pflanzenbauwissenschaften 30, Kiel, Germany, 35–36
Pao Y-C, Chen T-W, Moualeu-Ngangue DP, Stützel H
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2019. A mechanistic view of the reduction in photosynthetic protein abundance under diurnal light fluctuation. Journal of Experimental Botany 70, 3705–3708
Pao Y-C, Stützel H, Chen T-W
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2019. Environmental triggers for photosynthetic protein turnover determine the optimal nitrogen distribution and partitioning in the canopy. Journal of Experimental Botany 70, 2419–2434
Pao Y-C, Chen T-W, Moualeu-Ngangue DP, Stützel H
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2019. Functional adaptation strategies in photosynthesis to light and nitrogen availabilities of two highly productive cucumber cultivars with contrasting canopy structures. Mitteilung der Gesellschaft für Pflanzenbauwissenschaften 31, Berlin, Germany, 123–124
Pao Y-C, Chen T-W, Moualeu-Ngangue DP, Stützel H
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2020. Coordination between dynamics in canopy structure and photosynthetic acclimation strategy optimizes canopy productivity. Abstract Book, iCROPM 2020 International Crop Modelling Symposium, Montpellier, France, 58–59
Pao Y-C, Chen T-W, Stützel H
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2020. Experiments for in silico evaluation of optimality of photosynthetic nitrogen distribution and partitioning in the canopy: an example using greenhouse cucumber plants. Bio-Protocol 10, e3556
Pao Y-C, Chen T-W, Moualeu-Ngangue DP, Stützel H
