Nguyen Hong Anh

Thesis defended on 19.12.2023

Subject : "Connecting the dots between Crop Growth Models, Root Architecture Models, and High-throughput Root Phenotyping Platforms"

Abstract :
Crop growth models (CGMs) are powerful tools to understand, predict, and optimize crop performance under various environmental conditions and management practices. However, while aboveground growth and crop yield have been the main focus of CGMs, the representation of roots is often simplified or overlooked, hampering our capacity to account for potential improvement by breeding root architecture, uptake capacity, or plasticity in response to the environment. In parallel, more or less detailed root architecture models (RAMs) based on the sequential development, branching, and elongation of topologically connected and hierarchized organs with defined functions have been developed to account for a diversity of architectures and interactions with the surrounding rhizosphere. To better account for the role of root systems in crop performance, and specifically allow predicting potential benefits of specific architectural features of root systems such as branching capacity, root orientation, and vigor, a strategy is thus to couple RAMs and CGMs. The coupling of a wheat CGM (SiriusQuality) and a RAM (ArchiSimple) was performed in parallel with this thesis. This work stepped into this coupled model to explore three domains. First, we evaluated the capacity of two different high throughput root phenotyping (aeroponic or rhizotubes®) platforms under controlled conditions to capture the genetic variability of key ArchiSimple parameters. A significant effect of the experimental setup was found for all measured parameters while no significant correlation across a panel of 14 wheat cultivars could be detected. Differences in temperature and/or irradiance but also the developmental stage between experiments and setups may partly explain the differences observed, highlighting the need for considering both developmental and environmental drivers in root phenomics studies and RAM construction and parametrization. Second, using the coupled SiriusQuality::ArchiSimple model, five ideotypes with contrasted root architecture were simulated in a combination of seven European sites and four contrasted soil types during 30 consecutive growing seasons (1990-2020). Simulations confirmed that the benefits of specific root architectural features greatly vary depending on soil and climate. The carbon cost of these architectures as well as their environmental impact on water and minerals remain to be accounted for to fully consider their cost-benefit balance, in support of a more virtuous agriculture. Finally, using non-destructive observations of root development, we challenged the over-simplistic hypotheses of ArchiSimple about primary root emission as well as the dynamic of their elongation rate and diameter. We confirmed that in wheat, primary axis emission could be easily modeled from the knowledge of tillering dynamics while their elongation rate and diameter follow predictable patterns. These results provide the foundation to develop an improved version of ArchiSimple.

Management at LEPSE :

Bertrand Muller, thesis supervisor
Pierre Martre, thesis co-supervisor