Research progress on the uptake of organic nitrogen by terrestrial plants

In some ecosystems such as arctic tundra, alpine meadow and boreal forest where nitrogen mineralization is strongly limited, it is found that many plants are able to directly absorb organic nitrogen (N) in soil. This phenomenon urges people to rethink the traditional concept of terrestrial N cycling based on N mineralization. In this review, we analyze the recent work about the types of organic N that plants can absorb, the roles of mycorrhiza in these nutrition-acquiring processes and experimental designs and methods utilized in theses studies. The organic N sources that plants can absorb include free amino acids and low molecular weight peptides. The roles of mycorrhizal fungi and saprotrophic fungi are important during the process of obtaining N sources in polyphenol-protein complexes by plants. The design of organic N uptake experiments could be performed with the help of isotope techniques and mathematic models. In the future, how to examine the uptake of organic N by plants under field conditions needs to be carefully considered in research.