The Role of Mycorrhiza in Transformation of Nitrogen Compounds in Soil and Nitrogen Nutrition of Plants: A Review

Abstract

The role of mycorrhizal symbiosis as a control of the biogeochemical cycle of nitrogen in soils and in the nitrogen nutrition of plants is considered. The contribution of ericoid mycorrhiza (ErM) and ectomycorrhiza (EcM) to nitrogen (N) supply of host plants is well known, whereas the role of arbuscular mycorrhiza (ArM) is insufficiently understood. Exoenzymes released into the soil from the ErM and EcM mycelium favor the hydrolysis of high-molecular-weight N-containing organic compounds of plant litter and soils to \({\text{NH}}_{4}^{ + }\) or amino acids that are then transported toward plant roots and are absorbed by them. ArM-producing fungi have a limited capacity to release hydrolytic enzymes capable to decompose high-molecular-weight organic compounds into the soil (or do not have it at all). Therefore, they are specialized on the absorption of inorganic forms of N and amino acids appearing in the soil in the course of decomposition of high-molecular-weight N-containing compounds by saprotrophic microorganisms. The activity of hydrolytic exoenzymes and the role of mycorrhiza in the nitrogen nutrition of plants become more significant under conditions of the low supply with mineral N compounds and decrease upon the rise in availability of mineral N compounds. At the same time, mycorrhizal fungi and host plants may compete for the limited resource. The isotopic composition of N in plants (δ¹⁵N) and the fractionation of ¹⁵N isotope between the mycorrhizal fungi and host plants are considered indicative of the participation of mycorrhiza in the nitrogen nutrition of plants.