Dataset of a multi-pulse labelling experiment with 13C CO2 to trace root-derived carbon in the soil.

Description of the study The data provided here comes from an experimental study on root-derived carbon. We attempted to quantify SOCnew, which is here all the carbon released by the root that has not been sampled as root biomass, for 12 crop species. To do that, we performed a multi-pulse labelling of the plants with 13C-enriched CO2, to trace the fresh carbon into the soil. Then, we performed for 524 days a following incubation experiment, in the field, with litterbags, to assess the persistence of SOCnew and to compare it to that of roots. Description of the files This folder contains 6 csv files and 3 R codes. The latter are in the markdown format, so that they can be run by the user, and their corresponding html file is available for reading only. The files “Raw_Data_Horizon”, “t0” and “Incubation_data” are data files that serve as a basis for calculations. The two codes “SOCnew_calculation” and “incubation_experiment_calculations” perform calculations by using the latter data files. The results of the calculations are summarized in the three following files: “SOCnew_results_perhorizon”, “results_permesocosm” and “Incubation_results”. The code “statistical_analysis” provides a list of the tests performed with the data. Variable lists for the different data tables 1. Raw_Data_Horizon This data table reports the raw value per horizon (soil layer). Each mesocosm has two lines: one for the upper horizon and one for the lower horizon. •species_lat: latin name of the species •species: common name of the species •cell: climatic cell in which the mesocosm was placed. It stands as a replicate. The experiment was performed across three climatic chambers. Each species grew in a different climatic cell. •family: the plant family to which the species belongs •depth: Soil horizon. H = 0 – 20 cm and F = 20-45 cm •m_soil_bulkonly_105: mass of the bulk soil per horizon after correcting for the gravimetric humidity. Unit = kg. •m_soil_rhizosheat_105: mass of the rhizosheath soil per horizon after correcting for the gravimetric humidity. This is only the rhizosheath that was sampled, not the total rhizosheath that might be present in the column. The latter is estimated in another data table. Unit = kg. m_rhizosheath_105 + m_soil_bulkonly_105 = whole soil dry mass of the mesocosm per horizon. •SOLO_m_soil_rhizosheat_105: subsample of the previous rhizosheath mass “m_rhizosheath_horizon_105” that was carefully sampled for a single plant, for which the root system was weighted. This soil mass is used to calculate the whole rhizosheath soil mass in the mesocosm, by doing a cross product with the root masses. Unit = kg. •OC_bulk_tf: organic carbon concentration of the bulk soil at the end of the experiment. Unit = kg kg-1. •d13C_bulk_tf: δ13C isotopic signature of the organic carbon in the bulk soil at the end of the experiment. Unit = ‰. δ13Csample = 1000 * [(13C/12C)sample/ (13C/12C)PDB – 1] •OC_rhizosheath: organic carbon concentration of the rhizosheath soil at the end of the experiment. Unit = kg kg-1. Analysis was performed when at least 13 grams of soil was available. •d13C_rhizosheath: δ13C isotopic signature of the organic carbon in the rhizosheath soil at the end of the experiment. Unit = ‰. δ13Csample = 1000 * [(13C/12C)sample/ (13C/12C)PDB – 1]. Analysis was performed when at least 13 grams of soil was available. •OC_roots: organic carbon concentration of roots. Unit = kg kg-1. •d13C_roots: δ13C isotopic signature of roots. Unit = ‰. δ13Csample = 1000 * [(13C/12C)sample/ (13C/12C)PDB – 1] •OC_shoots: organic carbon concentration of aboveground biomass. Unit = kg kg-1. •d13C_shoots: δ13C isotopic signature of aboveground biomass. Unit = ‰. δ13Csample = 1000 * [(13C/12C)sample/ (13C/12C)PDB – 1] •dry_roots: dry mass of roots per horizon per mesocosm. Unit = kg. •SOLO_dry_roots: subsample of the previous root biomass, that was sampled separately with a careful recovery of the rhizosheath. It corresponds to the root biomass of one single plant, that was extracted by hand. If there is only one plant in the mesocosm, this biomass might still be different from the total root biomass of the mesocosm, as a part of root biomass was recovered with a sieve, after the extraction by hand. Unit = kg. 2. t0 This data table reports carbon concentrations for a subsample of mesocosms before sowing, at the beginning of the experiment. The sample is a composite sample of the soil horizon after homogenization and before potting. The data are used as a reference for further calculation on carbon inputs. •species: common name of the species •cell: climatic cell in which the mesocosm was placed. •depth: Soil horizon. H = 0 – 20 cm and F = 20-45 cm •t0_OC: Organic carbon concentration. Unit = kg kg-1. •t0_d13: δ13C isotopic signature of the organic carbon. Unit = ‰. 3. SOCnew_results_perhorizon This table reports the results of the calculations of SOCnew (rhizodeposition and fine root debris not sampled) and of rhizosheath mass, per horizon. •species: common name of the species •cell: climatic cell in which the mesocosm was placed. •family: the plant family to which the species belongs •depth: Soil horizon. H = 0 – 20 cm and F = 20-45 cm •SOCnew: quantity of SOCnew per horizon, i.e. net rhizodeposition and fine root debris < 2 mm, calculated with a mixing equation (1): SOCnew=δ13 Csoil−δ13 Creference δ13 Croot−δ13 Creference ×OCsample (1) with δ13Csoil and δ13Croot being the δ13C of the soil sample and of the corresponding labelled root respectively. δ13Creference is the δ13C of the soil before the plants were sown, at the corresponding horizon. Unit = kg. •M2_SOCnew: quantity of SOCnew per horizon, calculated with a mixing equation (2) using the isotopic signature of aboveground biomass as an end member this time: SOCnew=δ13 Csoil−δ13 Creference δ13 Cshoots−δ13 Creference ×OCsample (2) with δ13Csoil and δ13Cshoots being the δ13C of the soil sample and of the corresponding labelled aboveground biomass respectively. δ13Creference is the δ13C of the soil before the plants were sown, at the corresponding horizon. Unit = kg. •estimated_rhizosheath: mass of the estimated rhizosheath per horizon. Unit = kg. •SOCnew_estimated_rhizosheath: quantity of SOCnew per horizon in the rhizoseath. Unit = kg. 4. results_permesocosm This table reports observations and results of the previous calculation for the entire mesocosm. For instance, for SOCnew, both horizons have been summed. •species: common name of the species •cell: climatic cell in which the mesocosm was placed. •family: the plant family to which the species belongs •plant_number: plant density = number of plant per mesocosm •BBCH: phenological stage at the end of the experiment according to the BBCH scale (Meier 2003) •root_C: quantity of root carbon per mesocosm. Unit = kg. •shoot_C: quantity of aboveground biomass carbon per mesocosm. Unit = kg. •R_S_C: Root:Shoot ratio (root_C/shoot_C) for the whole mesocosm. •C_N_root: Carbon:Nitrogen ratio of roots •C_N_shoot: Carbon:Nitrogen ratio of aboveground biomass •SOCnew: SOCnew quantity. Unit = kg. •specific_SOCnew: specific SOCnew = SOCnew/root_C. Unit = kg kg-1. •estimated_rhizosheath: calculated rhizosheath mass. Unit = kg. •SOCnew_estimated_rhizosheath: calculated SOCnew quantity retrieved in the rhizosheath. Unit = kg. 5. Incubation_data This table reports the carbon data measured in the litterbags, as well as all the informations to calculate SOCnew and root decomposition. Each line stand for one litterbag •species: common name of the species •method: Type of litterbag. Method 1 = SOCnew decomposition (only labelled SOCnew) and Method 2 = root decomposition (unlabelled soil with labelled roots). •cell: climatic cell in which the mesocosm was placed during the previous experiments. Each cell is a replicate. •d13_bags: δ13C isotopic signature measured for the whole content of the bag at ti. Unit = ‰. δ13Csample = 1000 * [(13C/12C)sample/ (13C/12C)PDB – 1] •d13_roots: δ13C isotopic signature of the roots used as an end member in the isotopic mixing equation. Unit = ‰. •t0_soil_mass: mass of the fresh unlabelled soil added in the bags •t0_roots_mass: mass of the dry labelled roots added in the bags •family: the plant family to which the species belongs •days: days since the start of the incubation •OC_bags: organic carbon concentration in the whole bag. kg kg-1. •OC_roots: organic carbon concentration of the added roots. 6. Incubation_results This table reports the results of the incubation experiment. •species: common name of the species •cell: climatic cell in which the mesocosm was placed during the previous experiments. Each cell is a replicate. •days: number of days from the start of the incubation to the sampling •SOCnew_remaining: Calculated proportion of the labelled SOCnew retrieved in the bag at the sampling date. Unit = %. •roots_remaining: Calculated proportion of the labelled roots retrieved in the bag at the sampling date. Unit = %.