Revisiting diffusion-based moisture functions: why do they fail?

Diffusion-based moisture functions could provide insight into soil physical processes and potentially represent a more rigorous approach to model soil moisture-respiration relationships. However, large prediction bias remains when these functions are evaluated with field observations. Here we revisit the concept of diffusion limited substrate bioaccessibility by coupling Michaelis-Menten microbial uptake kinetics with linear mass transfer. The analytical solution of this microbial-substrate system demonstrates that moisture interacts with heterogeneous substrate distribution to control the dynamic transitions between diffusion-and reaction-limited regimes, leading to deviations of mean-field rates from spatially averaged rates. This result highlights the inadequacy of current simplified diffusion-based moisture functions in capturing the nonlinearity between substrate distribution and microbial utilization, and calls for continued development of effective upscaling approaches and experimental validation.

Automated summary

Diffusion-based moisture functions are inadequate in capturing the nonlinearity between soil moisture and microbial utilization, highlighting the need for further development of effective upscaling approaches and experimental validation.