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Organic carbon decomposition rates with depth and contribution of inorganic carbon to CO 2 emissions under a Mediterranean agroforestry system
Author(s) -
Cardinael Rémi,
Chevallier Tiphaine,
Guenet Bertrand,
Girardin Cyril,
Cozzi Thomas,
Pouteau Valérie,
Chenu Claire
Publication year - 2020
Publication title -
european journal of soil science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.244
H-Index - 111
eISSN - 1365-2389
pISSN - 1351-0754
DOI - 10.1111/ejss.12908
Subject(s) - topsoil , subsoil , soil carbon , environmental science , mineralization (soil science) , total organic carbon , soil water , soil organic matter , calcareous , soil science , agronomy , environmental chemistry , chemistry , geology , biology , paleontology
Agroforestry systems have been much studied for their potential to store soil organic carbon (SOC). However, few data are available on their specific impact on potential SOC mineralization, especially at depth in subsoils. Moreover, many soils of the world, especially in arid and semiarid environments, also contain large stocks of soil inorganic carbon (SIC) as carbonates. Consequently, the organic carbon dynamics have been poorly investigated in these soils due to the complexity of measurements and of the processes involved. To assess mineralization rates of SOC with depth, we incubated soil samples from an 18‐year‐old agroforestry system (both tree row and alley) and an adjacent agricultural plot established on a calcareous soil in France. Soil samples were taken at four different depths: 0–10, 10–30, 70–100 and 160–180 cm. Total CO 2 emissions, the isotopic composition (δ 13 C, ‰) of the CO 2 and microbial biomass were measured. The SIC concentrations ranged from 48 to 63 g C kg −1 soil and the SOC concentrations ranged from 4 to 17 g C kg −1 soil. The contribution of SIC‐derived CO 2 represented about 20% in the topsoil and 60% in the subsoil of the total soil CO 2 emissions. The microbial biomass and the SOC‐derived CO 2 emissions were larger in the topsoil, but the decomposition rates (day −1 ) remained stable with depth, suggesting that only the size of the labile carbon pool was modified with depth. Subsoil organic carbon seems to be as prone to decomposition as surface organic carbon. No difference in CO 2 emissions was found between the agroforestry and the control plot, except in the tree row at 0–10 cm. Our results suggest that the measurement of soil respiration in calcareous soils could be overestimated if the isotopic signature of the CO 2 is not taken into account. It also advocates more in‐depth studies on carbonate dissolution–precipitation processes and their impact on CO 2 emissions. Highlights We measured SOC mineralization and inorganic carbon contribution to CO 2 emissions in agroforestry Subsoil organic carbon was as prone to decomposition as surface organic carbon Inorganic carbon contribution to CO 2 emissions ranged from 20 to 60% depending on soil depth Measurement of soil respiration in calcareous soils could be overestimated