EGU2020-10139
https://doi.org/10.5194/egusphere-egu2020-10139
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Contribution of inorganic carbon to CO2 emissions under a Mediterranean agroforestry system

Tiphaine Chevallier1, Rémi Cardinael1,2,3, Bertrand Guenet4, Thomas Cozzi2, Cyril Girardin2, and Claire Chenu2
Tiphaine Chevallier et al.
  • 1Eco&Sols, IRD, CIRAD, INRA, Montpellier SupAgro, Univ Montpellier, Montpellier, France (tiphaine.chevallier@ird.fr)
  • 2AgroParisTech, UMR Ecosys, Avenue Lucien Brétignières, 78850 Thiverval-Grignon, France
  • 3CIRAD, UPR AIDA, F-34398 Montpellier, France
  • 4Laboratoire des Sciences du Climat et de l’Environnement, LSCE/IPSL, CEA-CNRS- UVSQ, Université Paris-Saclay, Gif-sur-Yvette, France

In the last years, soil organic carbon (SOC) dynamics have been explored for agronomic and environmental issues in different agro systems. Many soils of the world, especially in arid and semi-arid environments, contain large stocks of soil inorganic carbon (SIC) as carbonates. Yet, the SOC dynamics has been poorly investigated in these soils, due to the complexity of measurements and of the processes involved. Indeed, few previous studies have shown links between SIC and SOC dynamics. Theses interactions are initiated by biological activities, i.e. CO2 production, are explained through equilibrium equations between soil carbonates and bicarbonates. However, few data were available on the specific impact of SIC on SOC mineralization especially at increasing soil depth.

Alley agroforestry systems increased SOC content in the tree rows without any change in the SIC content.  The heterogeneity in organic inputs and SOC contents induced by alley agroforestry allows the investigation of the interactions between SIC and SOC on CO2 emissions.

To assess contributions of SIC to CO2 emissions with depth, we incubated carbonaceous soil samples coming from an 18-year-old agroforestry system (both tree row and alley) and an adjacent agricultural plot. Soil samples were taken at four different depths: 0-10, 10-30, 70-100 and 160-180 cm. Total CO2 emissions, the isotopic composition (δ13C, ‰) of the CO2 and microbial biomass were measured. The SIC concentrations were from 48 to 63 g C kg-1 soil and the SOC concentrations from 4 to 17 g C kg-1 soil. The total amounts of CO2 emissions from soil were correlated to C contents and decreased with depth (from 183-569 µgC g-1 soil in top soil vs 21-25 µgC g-1 soil in subsoil).

The contribution of SIC-derived CO2 was not homogenous along the soil profile. It represented about 20% in the topsoil and 60% in the subsoil of the total soil CO2 emissions. As the SOC content and the microbial biomass, the SOC-derived CO2 emissions were larger in the topsoil especially in the tree row compared to the alley and the agricultural plot. The SIC-derived CO2 emissions were also larger in topsoil and in tree rows at 0-10 cm than in alleys or agricultural plots (71 µg C g-1 soil vs 45-48 µg C g-1 soil) or in the subsoil (13-15 µg C g-1 soil), whereas the amount of SIC was similar in top and subsoil and in tree rows, alleys or agricultural soils. This indicate that CO2 emissions from SIC were linked to the SOC content and its mineralization.  In addition, our results suggest that the measurement of soil respiration in calcareous soils could be overestimated if the isotopic signature of the CO2 is not taken into account. It also advocates more in-depth studies on carbonate dissolution-precipitation processes and their impact on CO2 emissions.

Reference:

Cardinael, R., Chevallier, T., Guenet, B., Girardin, C., Cozzi, T., Pouteau, V., and Chenu, C. 2019 Organic carbon decomposition rates with depth and contribution of inorganic carbon to CO2 emissions under a Mediterranean agroforestry system, Eur J Soil Sci, https://doi.org/10.1111/ejss.12908.

How to cite: Chevallier, T., Cardinael, R., Guenet, B., Cozzi, T., Girardin, C., and Chenu, C.: Contribution of inorganic carbon to CO2 emissions under a Mediterranean agroforestry system, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10139, https://doi.org/10.5194/egusphere-egu2020-10139, 2020

Comments on the presentation

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Presentation version 1 – uploaded on 28 Apr 2020
  • CC1: Comment on EGU2020-10139, Ana López Ballesteros, 06 May 2020

    Congrats for the work done! I just wanted to share some previous work where we find relatively high CO2 emissions (using eddy covariance systems) in water-limited systems where biological activity is heavily restrited due to water stress. Although many of these sites have calcaric soils, we did not measure the relative fraction of CO2-flux associated to SIC. Here is an example:

    http://dx.doi.org/10.1016/j.agrformet.2016.12.021

    Best

    Ana

     

    • AC1: Reply to CC1, Tiphaine Chevallier, 06 May 2020

      Thank you for sharing your research.  I was wondering if what we have measured in jars can be also measureable on the field. Your work give a nice clue to answer. Thanks !

       

    • AC2: Reply to CC1, Rémi Cardinael, 06 May 2020

      Thank you Ana, very interesting!

      Apparently, it is also sometimes possible to detect massive changes in SIC stocks due to management, for example with N fertilization and resulting soil acidification. See this paper just out:

      https://onlinelibrary.wiley.com/doi/full/10.1111/gcb.15101

      Regards,

      Rémi

      • CC2: Reply to AC2, Ana López Ballesteros, 06 May 2020

        Thanks for the paper Remi! Very relevant when working with agricultural systems.