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 t he plant rhizosphere. Environmental factors affecting root exudation have b een identified but their effects are rarely quantified. The purpose of this work was to evaluate the impact of both the microflora and the chemical co mposition of the growth medium on root exudation, taking into account solub le exudates and mucilage ii-action. Maize plants (Zea mays L.) were grown f or 12 days in hydroponic conditions and then transferred in three root bath ing solutions (demineralized water, KCl or nutrient solution) during 24 hou rs. In each case, presence of microflora was tested with a comparison betwe en plants inoculated with maize rhizospheric strain and axenic plants. Exud ation was measured in terms of C and biomass production. A strong interacti on was noticed between microflora and chemical composition of the root bath ing solution. In fact, the presence of rhizospheric microflora induces a st imulation of soluble exudates only in KCl and Nutrient solutions. In demine ralized water, a different response was observed with a higher C release fo r axenic plants, probably due to the osmotic shock induced to the roots. Co ncerning mucilage fractions, small quantities were recovered on all treatme nts. This work demonstrates that the chemical composition of the root bathi ng solution and presence of microorganism significantly modify the amount o f soluble exudates. Attention must therefore be paid to the cultural condit ions when exudation is studied because of the sensitivity of this process t o root environment.