Root Processes Affecting the Soil Moisture Patterns in Ecohydrology

Soil moisture patterns arise from the combined processes induced by vegetation, soil properties, climate, topography, parent material, and time. In this chapter, we focus on how vegetation induces soil moisture patterns, particularly how plantroot processes affect the soil moisture distribution. Four different mechanisms were identified as potential drivers of soil moisture variability: root growth, root water uptake and transpiration, plant competitions, and rhizosphere properties. High transpiration, root growth, and root water uptake generally increase the soil moisture variability for drying conditions. On the other hand, other mechanisms reduce the soil moisture variation under drying condition including (1) compensation, which plants extract water in the wettest part of the soil; (2) hydrotropism, which roots tend to grow toward wetter zone of the soil; and (3) plant competition, which different plants try to segregate the depths at which they take up water. In addition, rhizosphere-specific properties tend to increase the variability when the soil is wetted from dry condition or to decrease it under wet conditions. We used a plant architecture model to illustrate how soil and root properties combine to generate or destroy soil moisture relations

Ranking of mechanisms governing the phytoavailability of cadmium in agricultural soils using a mechanistic model

Aims The objective of this study was to rank the mechanisms influencing the phytoavailability of cadmium(Cd) in agricultural soils.Methods We developed a model that simulates the transport by diffusion and convection, the kinetics ofsorption and complexation in solution and the root uptake of Cd. The ranking of mechanisms was performed by simulating the Cd2+ uptake by 1 cm2 root for 30 days for French agricultural soil characteristics.Results The initial Cd2+ concentration was the most influential parameter followed by the soil buffer power for Cd2+ and by the soil water content and impedance factor. The Cd2+ was generally strongly depleted at theroot surface and the convection was almost negligible. In general, the Cd complex dissociation contributedlittle to the uptake due to a strong kinetics limitation. Conversely, the kinetics of sorption was little influential.Conclusions The initial concentration and diffusion of Cd2+ were the dominant processes governing the phytoavailability in non-polluted soils. A model considering only the transport and sorption of Cd2+ without kineticswould be adequate to predict the phytoavailability. The particular situations where these simplifications do nothold (relative error >10 %) corresponded to a high supply of labile Cd complex toward plant roots

Root System Architecture

An increasing body of evidence indicates that the engineering of root system architecture has the potential to support a second green revolution targeting crop performance under suboptimal water and nutrient supply. This chapter summarizes the recent evolution of this field and underlines important challenges to be addressed in a near future. Due to its importance for many plant functions, root system architecture has become a topic on its own in many research communities. Impressive progress has been achieved in our understanding of the developmental processes underlying root system architecture, and, in parallel, a large number of QTL studies have been reported for root architectural traits. We discuss several limitations that impede the exploitation of the genetic variability and available functional information on root system architecture in conventional breeding

Phenotyping for Root Traits

Root system architecture determines crop capacity to acquire water and nutrients in the dynamic and variable soil environment. Increasing attention is paid to searching for optimal root traits to improve resource uptake efficiency and adaptation to heterogeneous soil conditions. This chapter summarises genetic variability and plasticity in root traits relevant to increased efficiency of soil resource acquisition. Approaches available for high-throughput phenotyping of root architecture traits at both laboratory and field scales are critically assessed. The advent of several novel imaging technologies such as X-ray computed tomography coupled with image-analysing software packages offers a great opportunity to non-invasively assess root architecture and its interactions with soil environments. The use of three-dimensional structure–function simulation root models is complementary to phenotyping methods, providing assistance in the crop breeding programmes. We also discuss applications and limitations of these novel visualisation technologies in characterising root growth and the root–soil interactions