Investigating soil-water-plant relations - From root segment modeling to field scale experiments by Axelle Koch

Plant transpiration is the main component of terrestrial evapotranspiration and represents about 40% of terrestrial rainfall. This huge amount of water is extracted from the soil by the plant root systems, which thereby play a crucial role in controlling soil moisture (SM) and its variability in time and space.

Functional-structural root-soil models (FSRSMs), which combine root functional and structural information have been developed to simulate carbon, water and nutrient transfers between plants, atmosphere and soils. These models can therefore help predict the impact of plant root architecture and the distribution of soil and root hydraulic properties on root water uptake (RWU) and investigate the key factors determining SM and RWU variability.

This PhD thesis is a combination of three-dimensional simulation at the plant scale and experimental work at the field scale to advance our comprehension of the hydraulic resistances in the soil-plant system that control transpiration and RWU. First, the 3D FSRSM R-SWMS was validated by combining root and tracer distributions obtained by magnetic resonance imaging (MRI) to inverse modeling. Second, we demonstrated the importance of rhizosphere resistance on the relationship between plant transpiration and leaf water potential. This result was obtained by using an FSRSM to represent the experimental behavior of two Maize genotypes (with and without root hairs). Finally, a field scale experiment highlighted that plant associations with complementary root systems did better tolerate water deficit than other associations by exploiting specific depth niches.