Biotic and Abiotic Factors on Soil Nutrient Diffusion Flux Based on Microdialysis: A Meta-Analysis

Diffusion is the primary driver of limiting nutrient transfer in terrestrial ecosystems, a process that is controlled by dynamic interactions between soil chemical, biological, and physical properties. These properties interact through complex mechanisms, and their impacts on diffusive fluxes vary significantly due to the inherent heterogeneity of soil environments. Building on Fick’s first law of diffusion, this study seeks to unravel the underlying relationships among key driving factors of nutrient diffusion in soil and to quantify their contributions using a mathematical approach.

Fick’s first law defines diffusion as the product of the diffusion coefficient times the concentration gradient, divided by the diffusive path length. Among these factors, the diffusion coefficient is therefore positively related with nutrient diffusion rates and is primarily influenced by soil chemical properties, such as pH, texture, and mineral type, and nutrient properties, such as molecular size and charge, driving nutrient sorption and immobilization reactions. Similarly, the concentration gradient between the diffusion source and sink acts as another positive driver, which is shaped by (i) dynamic source processes like organic matter mineralization, microbial turnover, and nutrient addition by fertilization and (ii) sink processes governed by biological uptake and sorption. In contrast, diffusive path length is negatively related to the diffusive flux, with longer path lengths reducing nutrient fluxes. Path length is largely determined by soil porosity and soil water content, highlighting the importance of physical soil properties and hydrology in regulating nutrient diffusion.

Through theoretical analysis, a comprehensive review of the existing literature and new measurements, we explore how these factors influence nutrient diffusion under varying land management types, across soils varying in soil pH and texture, and in biological activity. The ultimate goal of this study is to identify the primary drivers of soil nutrient diffusion, to quantify their relative contributions, and to establish a generalized mathematical model to describe their interrelationships. By adopting an integrative approach, this work aims to provide a comprehensive understanding of nutrient diffusion mechanisms across diverse soil environments, offering insights beyond single-factor and single-species studies.