Smucker, A. J. 1993. Soil environmental modifications of root dynamics and measurement. Annual Review Phytopathology 31:191-216.

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Morphology of root systems is directed by genetic codes and attenuated by historical and contemporary environmental conditions. Plant growth and survival rely upon continuous alterations by the root system, in response to the varied soil environments they inhabit. Net root-system geometry results from the combined expressions of dominant apical root meristems that successfully compete for plant photosynthates. Soil environmental conditions control the rates of extension and respiratory activities associated with root function. Soil water, nutrient, temperature, gaseous composition, microbial
inoculum and activities, mesofaunal interactions, carbon, and additional energy inputs control the net geometry and function of a specific plant root system. There is great diversity among root architectures; some of these diferences may be explained, in part, by adaptive responses although the agroecological significance of functional root architectures remains obscure.

Healthy and functional root systems are essential for the production of numerous resources used by animals, people and civilizations. To this end, the root-soil interface can be classified as one of the most important sites for inorganic and organic exchanges in support of life on this planet. Therefore, our knowledge of root health and function needs to move beyond contemporary single-parameter approaches, i.e. absorption along the total length of a uniformly distributed root system. Such single-parameter approaches greatly limit our understanding of the complexities of ion and water absorption by root systems. Similarly, root infection occurs at multiple sites along the root axis. Consequently, the description of root diseases, often rated as an index of infection or symptoms, needs to be expanded to include the intensity or the comprehensive nature of the invasion of host root systems. A description of root function and disease needs to include recent knowledge of dissimilar absorption and infection rates for each root segment within each soil horizon across both time and space. Unfortunately, these parameters of root function and disease have not been evaluated due to the paucity of quantitative methods for describing root-system geometry within the soil for the lifetime of each root segment. The absence of methods for nondestructively observing the biotic and abiotic conditions that promote root diseases has placed large constraints on our description and understanding of infection processes and associated losses of root function. Recent advances in nondestructive and quantitative evaluations of root morphology, discussed in this review, should improve future evaluations of the functional responses by roots to soilborne plant pathogens and their associated environments.

DOI: 10.1146/

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