The microbial immobilization of inorganic nitrogen (N) has a vital role in controlling the size of the soil inorganic N pool and is therefore an important mechanism for the retention of N in ecosystems. As the dominant microorganisms in soil, fungi and bacteria are probably the main participants in inorganic N immobilization. However, as a result of the high diversity and complexity of soil microorganisms, quantifying the respective rates of immobilization of inorganic N by fungal and bacterial communities in soil is challenging.

Amino sugars, which are important constituents of microbial cell walls, have different origins in microorganisms. Based on their microbial source specificity, stable isotope probing based on amino sugars has been developed to disentangle the immobilization processes of inorganic N by fungi and bacteria in soils. This approach has recently been extended to indicate the inorganic N immobilization rates of fungal and bacterial communities in soils. However, mainly as a result of the actual contents of amino sugars in the respective biomasses of fungi and bacteria and the turnover rates of cell N-containing components intracellularly and extracellularly in soil are unobtainable, directly converting the synthesis rates of ₁₅N-labeled amino sugars specific for fungi and bacteria to the actual inorganic N immobilization rates in soil is challenging.

To bypass the intractable problem mentioned above, the researchers from South China Botanical Garden of Chinese Academy of Sciences propose a mathematical framework to estimate the conversion coefficients between fungal and bacterial inorganic N immobilization rates and their respective proxies by combining the gross inorganic N immobilization rate with proxies for the respective inorganic N immobilization rates of fungi and bacteria. In this way, they can obtain the respective immobilization rates of inorganic N by fungal and bacterial communities in soil.

For further reading, please refer to: https://doi.org/10.1016/j.geoderma.2020.114450, https://doi.org/10.1016/j.soilbio.2020.108114.