Abstract
Abstract. Being the most common human-created landforms, terrace construction has resulted in an extensive perturbation of the land surface. However, our mechanistic understanding of soil organic carbon (SOC) (de-)stabilization mechanisms and the persistence of SOC stored in terraced soils is far from complete. Here we explored the factors controlling SOC stability and the temperature sensitivity (Q10) of abandoned prehistoric agricultural terrace soils in NE England using soil fractionation and temperature-sensitive incubation combined with terrace soil burial-age measurements. Results showed that although buried terrace soils contained 1.7 times more unprotected SOC (i.e., coarse particulate organic carbon) than non-terraced soils at comparable soil depths, a significantly lower potential soil respiration was observed relative to a control (non-terraced) profile. This suggests that the burial of former topsoil due to terracing provided a mechanism for stabilizing SOC. Furthermore, we observed a shift in SOC fraction composition from particulate organic C towards mineral-protected C with increasing burial age. This clear shift to more processed recalcitrant SOC with soil burial age also contributes to SOC stability in terraced soils. Temperature sensitivity incubations revealed that the dominant controls on Q10 depend on the terrace soil burial age. At relatively younger ages of soil burial, the reduction in substrate availability due to SOC mineral protection with aging attenuates the intrinsic Q10 of SOC decomposition. However, as terrace soil becomes older, SOC stocks in deep buried horizons are characterized by a higher temperature sensitivity, potentially resulting from the poor SOC quality (i.e., soil C:N ratio). In conclusion, terracing in our study site has stabilized SOC as a result of soil burial during terrace construction. The depth–age patterns of Q10 and SOC fraction composition of terraced soils observed in our study site differ from those seen in non-terraced soils, and this has implications when assessing the effects of climate warming and terrace abandonment on the terrestrial C cycle.
Highlights
Since post-Neolithic times, the construction of terraces has played an important role in the expansion and intensification of agriculture for food production (Brown et al, 2021)
Results showed that buried terrace soils contained 1.7 times more unprotected soil organic carbon (SOC) than non-terraced soils at comparable soil depths, a significantly lower potential soil respiration was observed relative to a control profile
Our results show that the buried soil layers have a significantly lower specific potential maximum heterotrophic respiration (SPR) than the non-buried layers (Fig. 4), indicating that carbon burial by terracing reduces soil potential respiration and is a mechanism that contributes to SOC stabilization in agricultural terraces
Summary
Since post-Neolithic times, the construction of terraces has played an important role in the expansion and intensification of agriculture for food production (Brown et al, 2021). The impact of terracing on soil organic carbon (SOC) stocks has been studied in diverse regions in Europe (Curtaz et al, 2015; Dunjó et al, 2003; Walter et al, 2003), Asia (Chen et al, 2020; Shi et al, 2019), South America (Antle et al, 2007), and Africa (Kagabo et al, 2013), the mechanisms responsible for the observed C gain and loss due to terracing are unclear Both positive and negative effects of terracing on SOC stock have been reported (Gao et al, 2020; Chen et al, 2020; Brown et al, 2021). This knowledge gap limits our ability to evaluate how SOC stocks in terraced systems will respond to present and future environmental change such as terrace degradation or land-use change
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