Influence of plant morphology on root exudation of maize subjected to mechanical impedance in hydroponic conditions

Mechanical impedance stimulates maize root exudation. The purpose of this work was to evaluate the direct effect of mechanical impedance on root exudation from the indirect effect involving root morphological modifications induced by mechanical impedance. Maize plants were grown in axenic hydroponic culture conditions for 4, 8, 12 and 16 days, and mechanical impedance was simulated by glass beads. At the end of the culture, exudation of plants in a nutrient solution was measured during 24 h. At harvest, plant growth and development parameters as well as carbon exudation were measured. The results demonstrated a major influence of mechanical impedance on root growth with a reduction in root elongation. Comparisons with previous studies in soil conditions have indicated that the glass-bead system realistically simulated mechanical impedance. The carbon exudation rate fluctuated from 0.2 to 1.2 mg C plant(-1) day(-1) and a fraction of this carbon (0.06 to 0.11 mg C plant(-1) day(-1)) was recovered from glass beads in impeded conditions. The difference in exudation between both treatments for comparable plant morphologies lead to the conclusion that the mechanical impedance had a direct effect on exudation rate. Correlations between plant morphology and root exudation suggest that root morphology is probably involved in the modification of root exudation.