Influence of microflora and composition of root bathing solution on root exudation of maize plants

Root exudation of carbon (C) plays a major role in processes occurring in the plant rhizosphere. Environmental factors affecting root exudation have been identified but their effects are rarely quantified. The purpose of this work was to evaluate the impact of both the microflora and the chemical composition of the growth medium on root exudation, taking into account soluble exudates and mucilage ii-action. Maize plants (Zea mays L.) were grown for 12 days in hydroponic conditions and then transferred in three root bathing solutions (demineralized water, KCl or nutrient solution) during 24 hours. In each case, presence of microflora was tested with a comparison between plants inoculated with maize rhizospheric strain and axenic plants. Exudation was measured in terms of C and biomass production. A strong interaction was noticed between microflora and chemical composition of the root bathing solution. In fact, the presence of rhizospheric microflora induces a stimulation of soluble exudates only in KCl and Nutrient solutions. In demineralized water, a different response was observed with a higher C release for axenic plants, probably due to the osmotic shock induced to the roots. Concerning mucilage fractions, small quantities were recovered on all treatments. This work demonstrates that the chemical composition of the root bathing solution and presence of microorganism significantly modify the amount of soluble exudates. Attention must therefore be paid to the cultural conditions when exudation is studied because of the sensitivity of this process to root environment.