Models uncover how plants coordinate architectural characteristics and photosynthetic nitrogen allocation to optimize photosynthesis.

A plant’s overall growth form and the arrangement of its parts, or architectural characteristics, impact the quantity of sunlight energy that reaches the leaves within the canopy. This, in turn, affects photosynthesis, which is essential for plant growth and the production of biomass.

The efficiency of photosynthesis is heavily reliant on the limited nitrogen available for investment in proteins responsible for harvesting light energy and converting that energy into carbohydrates (carboxylation). The optimal allocation of nitrogen between these two photosynthetic functions is vital for achieving efficient photosynthesis and is referred to as their photosynthetic acclimation strategy.

During her doctoral work at Leibniz Universität Hannover, Dr. Yi-Chen Pao led a study on the coordination between photosynthetic acclimation strategy and architectural characteristics to maximize canopy photosynthesis. This work was recently published in the journal in silico Plants.

For the first experiment, the authors employed a mechanistic model of cucumber that was previously developed by Pao and colleagues to investigate the optimal coordination between photosynthetic acclimation strategy and architectural characteristics. They conducted simulations of plants with varying leaf angles and observed the patterns of photosynthetic nitrogen allocation. The parameter values used in the models were obtained from previous studies.

They found that nitrogen investment in light harvesting was higher than for conversion of carbohydrates under conditions leading to low canopy light penetration. This included times early in the day when the cumulative sunlight exposure was low and when leaves were more horizontal, resulting in self-shading.

In a second experiment the authors tested if optimal coordination between photosynthetic acclimation strategy and architectural characteristics could be observed in real-world cucumber varieties. They chose two contrasting cultivars:

The two cucumber cultivars used in experiment 2.
  • Aramon had larger, more vertical leaves and
  • SC-50 had smaller, more horizontal leaves.

Plants were grown under optimal greenhouse conditions. Over three weeks, researchers conducted measurements of various architectural characteristics of the plants, such as leaf angle, leaf area index, and the extent of light penetration through the canopy. Additionally, they measured photosynthesis and leaf nitrogen, which were used to calculate the photosynthetic nitrogen pools.

The real-world experiment confirmed their in silico findings: nitrogen investment was prioritized to carboxylation under high light and to light harvesting under low light for both cultivars. “It is not surprising that the simulation accurately predicted real-world responses. It’s amazing how plants can adapt to their environment, and we are able to capture that using simple models,” said Pao.

To determine if the two cultivars had optimal coordination between architectural characteristics and photosynthetic acclimation strategies when grown in a canopy, they ran the model simulations again, this time including architectural parameters derived from the real-world cultivar experiment. The cultivar-specific parameters included the architecture (leaf angle, size, and density) and proportion of leaf nitrogen partitioned to photosynthesis. The theoretical optimal partitioning of nitrogen between light capture and the conversion of carbohydrates was determined as the combination that resulted in the highest daily rate of photosynthesis.

Results from experiment three. Simulated optimality of photosynthetic nitrogen partitioning over a spectrum of light availability. Teal triangle is SC-50 and salmon diamond is Aramon.

Adherence to optimality varied over the spectrum of light availability for both cultivars, but SC-50 was closest to optimal. “SC-50 has horizontal leaves which capture more light, and more responsive nitrogen partitioning, which allows it to meet the needs of leaves exposed to different light levels. This is a smart strategy for coordinating function with architecture under strong light competition,” explained Pao.

The utilization of computational models played a pivotal role in offering a comprehensive viewpoint on genotypic variation in photosynthetic acclimation strategies, canopy architectures, and their optimal coordination in this study.

READ THE ARTICLE:

Yi-Chen Pao, Hartmut Stützel, Tsu-Wei Chen, Optimal coordination between photosynthetic acclimation strategy and canopy architecture in two contrasting cucumber cultivars, in silico Plants, Volume 5, Issue 2, 2023, diad014, https://doi.org/10.1093/insilicoplants/diad014


This article is part of the special issue on Multiscale Modelling of Photosynthesis

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