Arbuscular mycorrhiza and soil organic nitrogen: network of players and interactions

Abstract

Arbuscular mycorrhizal (AM) symbiosis is heavily and positively implicated in phosphorus (P) acquisition from soil to plants, including many important agricultural crops. Its role in plant nitrogen (N) nutrition is generally not as prominent or beneficial, with exception of some situations when N is available predominantly in organic forms. Yet the AM fungi (AMF) are, due to their poor exo-enzymatic repertoire, unlikely to degrade organic compounds on their own, therefore they possibly depend on other microorganisms to liberate nutrients contained in those materials. Here, we review current knowledge on the roles played by the AMF in plant N nutrition in general and uptake of N from organic compounds in particular, with a specific reference to microbes and processes involved in liberation and AM fungal utilization of N from organic compounds. Future research needs and directions are outlined, as is the agronomic and societal context of such research.

Dual‐mycorrhizal plants: their ecology and relevance

“…In the field, root exudation in AM trees appears to result in increased inorganic N in the rhizosphere, whereas the extracellular enzymes stimulated by root exudates in EM root systems resulted in increased availability of amino acids . Hence, the traditional view is that an AM or AM-dominated dualmycorrhizal plant may be able to gain access to additional organic N and P by allowing colonization by EM fungi, but access to organic nutrients by AM fungi may have been underestimated (Jansa et al, 2019). This is a topic ripe to be examined using dual-mycorrhizal hosts.…”

Photosynthetic Traits and Nitrogen Uptake in Crops: Which Is the Role of Arbuscular Mycorrhizal Fungi?

“…Among fertilizers, the chemically synthesized nitrogen (N) was the main player, considering that its production via the Haber-Bosch industrial process accounted for about 2% of world’s annual energy output [ 24 ]. This massive production posed risks for environment and human health and once applied lead to soil quality loss [ 25 , 26 ]. Considering the ongoing climate changing and the consequent predicted stress scenarios that includes novel plant pathogens, intense abiotic stresses (e.g., drought and salinity) and low availability of organic N and phosphorus fertilizers, novel environmental friendly management options (e.g., smart-climate agriculture, including crop diversification and the use of beneficial root-associated microorganisms) are under scrutiny [ 26 , 27 ].…”

“…Nowadays it is well recognized that AM symbioses are able to provide many ecosystem services to their hosts, including nutrients transfer from the soil (e.g., P, zinc, copper), although less importance to N cycling and acquisition have been imputed to AMF [ 26 ].…”

“…Interestingly, genes encoding for the chitin monomer N-acetylglucosamine transporters and metabolism have been documented in Rhizophagus irregularis . These findings opened new questions about the potential AM fungi-chitinolytic capacity and the consequent N uptake that still remain to be addressed [ 26 , 63 ].…”

Higher temperatures and lower annual rainfall do not restrict, directly or indirectly, the mycorrhizal colonization of barley (Hordeum vulgare L.) under rainfed conditions

“…It has been demonstrated that N concentration in AMF mycelium was higher (5%), as compared to the plant shoots and roots (� 1%) [65]. This could be explained by the substantial nitrogen demand of AMF for the synthesis of protein and chitin, the main constituents of their cell walls [66,67].…”