Abstract:

Arbuscular mycorrhizal fungi （AMF） could form symbionts with host plants and were widely found in terrestrial ecosystems， and AMF could significantly enhance the nitrogen （N） absorption capacity of host plants. The symbiosis of AMF with hosts could promote the absorption of N of plants through direct and indirect ways. The direct way was to improve the root traits， expand the total area and active absorption area of root by symbiosis of AMF and hosts. In addition， mycelium was formed in plant roots to expand the exploration area of soil. At the same time， extraneous mycelia could also form mycelial bridge between host roots to improve the N absorption capacity and N communication between hosts. The indirect way was that mycorrhizal symbiosis could promote the increase of host’s root secretion and mycelial secretion， and improve soil Nabsorption of hosts. In addition， mycelium could carry a large number of bacteria， and mycelium secretions could stimulate the growth and activity of microorganisms， and then changed the microbial composition of host’s roots. Meanwhile， the interaction between AMF and rhizobium could improve the host’s ability to fix N and absorb N. In addition of affecting the host’s absorption of N， AMF could also affect the host’s transport pathway of N. It showed the extraneous mycelia in mycorrhizal symbionts absorbed inorganic N in the soil and converted the inorganic N into arginine （Arg）， which was transported to the mycelia in the root through mycelia， where Arg was decomposed into urea and ornithine （Orn）， and NH{}_{\mathrm{4}}^{+}-N was formed again through the cycle of ornithine. And the NH{}_{\mathrm{4}}^{+}-N was transfered to host cells via ammonium transporter （AMT） for plant growth. The effects of AMF on nitrogen uptake and N transport in plants were reviewed， which provided a reference for mycorrhizal interaction in plant N uptake and transport.

Key words: arbuscular mycorrhizal fungi, nitrogen, route of transit

摘要：

丛枝菌根真菌（arbuscular mycorrhizal fungi，AMF）能与寄主植物形成共生体，广泛存在于陆地生态系统中，接种AMF可使寄主植物具有更强的氮（N）素吸收能力。AMF与寄主共生能够通过直接与间接途径促进植物对N的吸收。直接途径为AMF与寄主共生可改善植物根系性状，扩大根吸收总面积与活跃吸收面积，并在植物根部形成菌丝，扩宽对土壤的探索面积；同时，根外菌丝还可在寄主根间形成菌丝桥，提升寄主间N吸收能力及N的交流。间接途径为菌根共生可促进寄主根分泌物以及菌丝分泌物的增加，提高寄主对土壤N素的吸收；此外，菌丝能够承载大量细菌，且菌丝分泌物能刺激微生物生长与活性，进而改变寄主植物根系微生物组成；同时，AMF与根瘤菌互作能够提升寄主对N素的固定与吸收能力。AMF除影响寄主对N的吸收外，还可影响寄主体内N的转运途径，主要表现为菌根共生体中根外菌丝吸收土壤中的无机N，将无机N转化成精氨酸（arginine，Arg），通过菌丝体运输到根内菌丝，被分解成尿素和鸟氨酸（ornithine，Orn），通过鸟氨酸循环再次形成NH{}_{\mathrm{4}}^{+}-N，并通过铵转运蛋白（ammonium transporter，AMT）将NH{}_{\mathrm{4}}^{+}-N转移给寄主细胞，供植物生长所需。综述了AMF影响植物对N素吸收及N素转运机制的研究，以期为菌根互作对植物N素的吸收和转运研究提供参考。

关键词: 丛枝菌根真菌, 氮素, 转运途径