LAUSR

Background and aimsUnder the scenario of global change, continuous 13C-enriched CO2 labeling is a powerful tool for evaluating the interaction between plants and soil, especially the influence of elevated CO2 on the input of plant-derived C (new C) into soil in the short term. However, the methodological validity concerning the acquisition of isotopic signals and their implications in plants and soil remains ambiguous.MethodsWe conducted an experiment simulating elevated CO2 with wheat planted in growth chambers. 13C-enriched CO2 with identical 13C abundance was supplied at two CO2 concentration levels (350 versus 600 ppm) until wheat harvest. The δ13C values of plant tissues and soil were measured periodically during the growing season.ResultsThe δ13C values of wheat tissues under elevated 13CO2 were 15–17% higher than those under ambient 13CO2 after the heading stage, implying that the 13C signals themselves in plants and soil were not directly representative of the influence of elevated CO2 on the C fixation in the plant and thereby the flow of plant-derived C into soil. The proportion of plant-derived C in the soil (fnew) was calculated separately at each CO2 concentration by taking the initial soil as a reference and the corresponding δ13C values as parameters in the mixing model, and we found that elevated CO2 significantly enhanced the new soil C input by approximately 35.5% during our 62-day labeling. In our experiment, the fnew value under elevated CO2 could be overestimated by up to 1.7 times if the alteration of 13C signatures in photosynthates caused by the change in CO2 concentration is ignored.ConclusionsFor methodological clarification, we suggest that 1) 13C labeling is essential in all CO2 treatments to achieve CO2 concentration-dependent 13C signals in plants and soil, and that 2) the influence of elevated CO2 on soil C turnover can be estimated by the difference in the fnew under the two CO2 concentrations.