Towards a quantification of the interactions between soil architecture and microbial dynamics under a dynamical soil architecture

Over the last decade, the joint development of soil imaging tools and microscale models has made possible to start quantifying the role of soil architecture on soil functions and in particular on soil microbial activity. Microscale heterogeneity of soils have been considered to explain the microbial response, developing the concept of ‘hot-spots'. A major result highlighted from these studies is that spatial accessibility between the trophic resource and soil microorganisms is a key factor (Dungait et al., 2012). Under conditions of limited access, the decomposition of soil organic matter can be drastically reduced, whereas under conditions of optimal access the physiological traits of the microorganisms control the decomposition rate (Vogel et al., 2018). Interactions between soil architecture and microbial dynamics can also be indirect through the degree of soil pore aeration. For instance, the spatial accessibility between particulate organic matter and aerated soil pores can be related to the N₂O production of soil samples (Ortega et al., 2023). New indicators quantifying the spatial accessibility are now emerging (Mbé et al., 2021 ; Rohe et al., 2021). Such spatial indicators of soil heterogeneity could feed the pedotransfer functions used to modulate organic matter decomposition rate in macroscale models of soil carbon dynamics. However the relevance and the robustness of these indicators to explain microbial activity remain to be evaluated (Schlüter et al., 2022). They have been established for static environmental conditions while soil architecture is highly dynamical, continuously changing under biotic and abiotic factors. Due to the complexity of obtaining sequential imaging datasets, few studies have imaged the 3D dynamics of soil architecture (Bottinelli et al., 2016). Mathematical models simulating the deformation of the 3D arrangement of solid particles using geomechanics laws for granular media (Duriez & Galusinski, 2021) or using fractal approaches for simplified soils (Perrier, 1995) have been developed. Other microscale modelling studies have attempted to simulate soil architecture dynamics through the action of microbes or physico-chemical processes using simplified rules (Crawford et al., 2012 ; Rupp et al., 2019). These incentive models have yet to be used to simulate microbial soil functions. We discuss these approaches and how they could be used to investigate to what extent the dynamics of soil architecture modifies the spatial accessibility between organic matter and microorganisms and in fine the soil organic matter decomposition rate.

 

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