ALBERT

Description: Aims Application of carbon (C) and nitrogen (N) isotopes is an essential tool to study C and N flows in plant-soil-microorganisms systems. When targeting single plants in a community the tracers need to be added via e.g., leaf-labeling or stem-feeding approaches. In this study we: (i) investigated if bicarbonate can be used to introduce 14 C (or 13 C) into white clover and ryegrass, and (ii) compared the patterns of 14 C and 15 N allocation in white clover and ryegrass to evaluate the homogeneity of tracer distribution after two alternative labeling approaches. Methods Perennial ryegrass and white clover were pulse labeled with 15 N urea via leaf-labeling and 14 C either via a 14 CO 2 atm or with 14 C bicarbonate through leaf-labeling. Plants were sampled 4 days after labeling and prepared for bulk isotope analysis and for 14 C imaging to identify plant parts with high and low 14 C activity. Subsequently, plant parts with high and low 14 C activity were separated and analyzed for 15 N enrichment. Results Bicarbonate applied by leaf-labeling efficiently introduced 14 C into both white clover and ryegrass, although the 14 C activity in particular for white clover was found predominantly in the labeled leaf. Using 14 C imaging for identification of areas with high (hotspots) and low 14 C activity showed that 14 C was incorporated very heterogeneously both when using bicarbonate and CO 2 as expected when using pulse labeling. Subsequent analysis of 15 N enrichment in plant parts with high and low 14 C activity showed that 15 N also had a heterogeneous distribution (up to two orders of magnitude). Conclusion Bicarbonate can efficiently be used to introduce 14 C or 13 C into plant via the leaf-labeling method. Both 14 C and 15 N showed heterogeneous distribution in the plant, although the distribution of 15 N was more even than that of 14 C.