A gnotobiotic system for studying root carbon release using lettuce (Lactuca sativa L.)

A cultivation system was developed for studies of root exudation and plant-microbial interactions under gnotobiotic, hydroponic conditions. The system was tested by determining root carbon release from lettuce (Lactuca sativa L. cv. Grand Rapids) grown axenically at different ionic strengths for 3 weeks. Growth of the axenic plants was similar at 25, 50 or 100% of the full strength nutrient solution (NS) during the first 2 weeks. After 3 weeks, however, plant dry weights and total uptake of K, Ca, P, S, Mn, Fe, Zn and Cu were highest when the full strength NS was supplied. Also, the concentration of dissolved organic carbon (DOC) in the NS was higher in the 100% compared with the more dilute NSs. Estimated net root release of DOC after 3 weeks varied from 6 to 14 mg g(-1) root dry weight. The DOC relative release rate (RRR) was lower than the relative plant growth rate (RGR), indicating a reduction of the amount of DOC released per gram root dry weight with increasing plant growth. We conclude that the cultivation system allows axenic studies of root carbon release during 3 weeks with a high number of experimental units and a low incidence of contamination. (C) 2003 Elsevier B.V. All rights reserved.