EGU23-12839
https://doi.org/10.5194/egusphere-egu23-12839
EGU General Assembly 2023
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

Dynamics and stability of soil organic matter: climate vs. time

Giorgio Galluzzi1, César Plaza2, Simone Priori3, Beatrice Giannetta1, and Claudio Zaccone1
Giorgio Galluzzi et al.
  • 1University of Verona, Department of Biotechnology, Verona, Italy (giorgio.galluzzi@univr.it)
  • 2Consejo Superior de Investigaciones Científicas, Instituto de Ciencias Agrarias, Madrid, Spain
  • 3University of Tuscia, Department of Agricultural and Forestry Sciences, Viterbo, Italy

This study aims to investigate the mechanisms of soil organic carbon (SOC) sequestration with depth as a function of time and climate. Two chronosequences located along a climate gradient were investigated. The first chronosequence (ADI) consisted of fluvial terraces, whereas the second (LED) of fluvio-glacial terraces. Four sites (Q2, Q3, Q4 and Q5) located in 3 terraces (T1, T2, and T3), with age ranging from about 125,000 to 2,000 yr, were investigated for ADI, while 3 sites (Q1, Q2, and Q3) in 3 terraces (T1, T2, and T3, respectively), with age range from about 16,000 to 10,000 yr, were selected for LED. All sites were grasslands. Soil samples were collected (1 profile and 2 cores per site) by horizon, and each horizon sub-sampled by depth (each 5 cm). The sub-samples were characterized for pH, EC, total organic C, total N, texture, mineralogy, total and extractable elements, and for soil respiration. Particulate organic matter (POM) and mineral-associated organic matter (MAOM) were isolated and characterized by elemental and thermal analyses.

In ADI, the oldest site (ADIQ2) stocks 2 times more C in the topsoil (15 cm) than the youngest site (ADIQ5) (60 and 27 MgC/ha, respectively). Furthermore, in ADIQ3, 38% of the total SOC accumulated between 30 and 80 cm (48 MgC/ha). In LED, the youngest site (LEDQ3) shows the highest SOC stock to both 15 and 30 cm (86 and 138 MgC/ha, respectively). In LEDQ1, 46% of the total SOC accumulated between 30 and 90 cm (94 MgC/ha). Among sites having same age but different climate, LEDQ3 (the wettest and coldest site) stocks ~2 times more carbon than ADIQ3 (the driest and warmest site) to the first 30 cm of depth.

In LED, the ratio between the organic C in MAOM/POM in the topsoil ranges between 0.6 and 1.8, while in ADI between 1.1 and 3.9. Thermal indices (e.g., WL400-550/200-300, TG-T50) show that the stability of bulk SOM and pools generally increased with depth in ADI sites, whereas remained constant in LED. ADI soils had similar cumulative respiration (RHCUM), whereas LEDQ3 exhibited the highest RHCUM along the first 30 cm. Indeed, LEDQ3 had a 3× higher RHCUM than ADIQ3 in topsoil.

Our data show that significant amounts of organic C were accumulated in deeper soils (>30cm). Moreover, soil organic matter (SOM) stability, and especially that of MAOM, in ADI increased with depth. The relative contribution of POM to C storage was more important in LED than in ADI, especially in the topsoil. Overall, our data suggest that climate has a greater influence on the size of SOC stocks than age, which in turn exerts a major influence on the stability of SOM.

How to cite: Galluzzi, G., Plaza, C., Priori, S., Giannetta, B., and Zaccone, C.: Dynamics and stability of soil organic matter: climate vs. time, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-12839, https://doi.org/10.5194/egusphere-egu23-12839, 2023.