Challenges and opportunities for quantifying roots and rhizosphere interactions through imaging and image analysis

The morphology of roots and root systems influences the efficiency by which plants acquire nutrients and water, anchor themselves and provide stability to the surrounding soil. Plant genotype and the biotic and abiotic environment significantly influence root morphology, growth and ultimately crop yield. The challenge for researchers interested in phenotyping root systems is, therefore, not just to measure roots and link their phenotype to the plant genotype, but also to understand how the growth of roots is influenced by their environment. This review discusses progress in quantifying root system parameters (e.g. in terms of size, shape and dynamics) using imaging and image analysis technologies and also discusses their potential for providing a better understanding of root:soil interactions. Significant progress has been made in image acquisition techniques, however trade-offs exist between sample throughput, sample size, image resolution and information gained. All of these factors impact on downstream image analysis processes. While there have been significant advances in computation power, limitations still exist in statistical processes involved in image analysis. Utilizing and combining different imaging systems, integrating measurements and image analysis where possible, and amalgamating data will allow researchers to gain a better understanding of root:soil interactions. This article reviews the progress made in phenotyping roots using imaging and image analysis and looks forward to the potential of using the developed techniques to understand the integral interactions of roots and their rhizosphere. While discussing the utility of different techniques it also discusses the potential of combining phenotyping methods to gain a greater understanding of the dynamic processes involved in root rhizosphere interactions. Since roots are highly responsive to both the biotic and abiotic elements of the soil environment increasing our understanding of root rhizosphere interactions is a necessary step in truly understanding root function and efficiency, in varied and variable, environments.