Soil organic carbon dynamics matching ecological equilibrium theory

Abstract

The persistence of soil organic carbon (SOC) has traditionally been explained as a combination of recalcitrance properties and stabilization processes, which lead to the formation of complex organic compounds. However, recent conceptual advances and experimental evidence challenge this view. Here, we test these conceptual advances using a dynamic equilibrium theory of SOC founded on classic ecological theory. We postulate that the persistence of SOC is an equilibrium point where SOC losses resulting from continuous decomposition and SOC gains due to SOC protection are balanced. We show that we can describe the temporal dynamics of SOC remarkably well (average and median R 2 = 0.75) in publicly available SOC time series from experiments that investigated the effects of agricultural practices in arable soils. The predictive power of our simplistic model is not meant to compete with that of current multi‐pool SOC models or recent developments that include microbial loops. The simplicity of our analysis can, however, show how the conceptual distinction between the forces that control SOC loss and gain, and their equilibrium, can shed light on SOC dynamics. Specifically, our analysis shows that, regardless of specific mechanisms, the persistence of SOC will depend on the ultimate equilibrium between SOC gains and losses, which may depend on environmental (e.g. temperature) and ecological (e.g. spatially structured microbial activities) factors and the relative roles of these factors. Future experimental studies should quantify these roles to formulate a new generation of SOC dynamics model.

Modeling Organic Carbon Accumulation Rates and Residence Times in Coastal Vegetated Ecosystems

“…These counteracting OC dynamics were further illustrated at SM10 and SM15, which contained very similar OC stocks (99 and 98 Mg OC ha −1 , respectively) with contrasting CARs and transit times. These results fall in line with ecological equilibrium theory, which posits that soil OC persistence depends on the dynamic equilibrium between continuous losses (decay) and gains (inputs), and the extent to which protection mechanisms affect the rate of OC turnover (Caruso et al, ). Although this may be intuitive, it highlights the need to quantify OC transit times in blue carbon ecosystems because CARs alone only provide part of the picture.…”

Soil carbon sequestration potential of planting hedgerows in agricultural landscapes

“…The capacity of soils to sequester carbon is finite and soils will reach equilibrium depending on the quantity and quality of organic inputs ( Caruso et al, 2018 ) and soil properties; therefore, SOC sequestration beneath hedgerows will not continue indefinitely. For example, Falloon et al (2004) assumed that it would take between 50 and 100 years for soil carbon to reach a new equilibrium following a land use change.…”

“…Soil disturbance associated with planting a new hedgerow can result in compaction of the soil and displacement of the organic layer to deeper within the soil profile ( Laganière et al, 2010 ). This may result in higher estimates of SOC stock and sequestration rate in the initial years after planting, which, together with SOC stock saturation as soils reach a new equilibrium ( Caruso et al, 2018 ), could bias the interpretations of the long-term effects of hedgerows planting on SOC stocks and SOC sequestration rates. Thus, to assess the impact of hedgerow planting in the long term, we considered the sequestration rate of the oldest hedgerows of known age (i.e.…”

Ensemble modelling, uncertainty and robust predictions of organic carbon in long‐term bare‐fallow soils

“…The decomposition rates of individual pools in such multi‐pool SOC models are typically controlled by vastly different reaction coefficients that can result in highly non‐linear behaviour of the overall system (e.g. Caruso et al., 2018). The initial list included 34 models, but eight of them were excluded from further analysis because they showed severe limitations to run properly either under bare‐fallow soils or under the given climate conditions.…”