The objective of this proposal is to clarify factors influencing morphological variation in plant roots by examining genotypic differences in root system structure and responses to soil nitrogen (N) and water. The infertile wild and cultivated accessions of lettuce (Lactuca serriola and L. sativa) will provide a devierse set of germplasm adapted to a wide range of soil water and nutrient regimes. Genotypic differences in root system structure and plastic responses to enriched soil microsites will be studied using root topological methods and growth rate measurements. Ability to extract water, ammonium, and nitrate from enriched microsites will be studied using the root topological method, growth rates, measurements of plant water balance including both direct (stomatal conductance, leaf water potential) and indirect measurements (stable carbon isotope discrimination), and short-term labeling with the stable isotope, 15N. Improved understanding of environmental effects on root growth, including differences in response among genotypes, will provide a basis for improving water and N absorption of cultivated lettuce, a shallow-rooted crop with high demand for fertilizer N and irrigation inputs.
