Plants allocate a significant fraction of their biomass to sub-surface root systems. The resulting root systems are complex networks whose structural properties influence plant functions such as anchorage and resource uptake. However, the quantitative link between plant structure and plant function remains unclear because of the paucity of data on the spatial and temporal distribution of root systems for the majority of plant species. One of the main barriers to analysis is the lack of non-invasive experimental methods to monitor and characterize the growth of plant root systems dynamically in time. Here, we utilize a recently developed gel-based growth and imaging system to characterize root system architecture (RSA) properties of 10 different varieties of rice (Iyer-Pascuzzi et al., in prep). Using this system we observe the growth of complex root systems and automatically measure properties of the network as a whole after germination. These ontogenetic series reveal different profiles of root growth and allow us to characterize invariant features of root system growth (when they exist) as well as heritable phenotypic differences between varieties.
The dynamics of a growing root network are assessed by automatically computing a set of 12 structural properties related to how a root network grows in space. Several of the properties we estimate, such as specific root length and average root width, are already known to be important factors contributing to plant fitness. In particular, we find that some properties, such as network area and total length, grow linearly with time for all varieties. Quantification of multiple individuals for each variety demonstrates that growth profiles are heritable and that intra-variety differences of linear growth rates are less than between-variety differences. We also present preliminary evidence for allocation tradeoffs in rice root system growth between extension (as measured by the depth of a root system) and exploration (as measured by the number of roots). Varieties which allocate more biomass to extension immediately after germination show less exploration capacity, whereas the converse also holds – over the first two weeks of growth. Finally, we describe ongoing attempts to characterize those aspects of root system development that are most conserved and those that are most divergent between rice varieties as part of ongoing efforts for improving crop yields and crop resilience.