Rhizodeposition in maize: short-term carbon partitioning

The aim of this study was to assess differences in rhizodeposition quantity and composition from maize cropped on soil or on 1:1 (w/w) soil–sand mixture and distribution of recently assimi-lated C between roots, shoots, soil, soil solution, and CO2 from root respiration. Maize was labeled in 14CO2 atmosphere followed by subsequent simultaneous leaching and air flushing from soil. 14C was traced after 7.5 h in roots and shoots, soil, soil solution, and soil-borne CO2. Rhizodeposits in the leachate of the first 2 h after labeling were identified by high-pressure liquid chromatography (HPLC) and pyrolysis–field ionization mass spectrometry (Py-FIMS). Leachate from soil–sand contained more 14C than from soil (0.6 % vs. 0.4%) and more HPLC-detectable carboxylates (4.36 vs. 2.69 lM), especially acetate and lactate. This is either because of root response to lower nutrient concentrations in the soil–sand mixture or decreasing structural integ-rity of the root cells during the leaching process, or because carboxylates were more strongly sorbed to the soil compared to carbohydrates and amino acids. In contrast, Py-FIMS total ion intensity was more than 2 times higher in leachate from soil than from soil–sand, mainly due to signals from lignin monomers. HPLC-measured concentrations of total amino acids (1.33 l