外生菌根共生对林木氮素吸收的促进作用

外生菌根真菌能与某些树木形成稳定的菌植共生体——外生菌根。外生菌根能吸收土壤中植物难以吸收的无机或有机形式营养物质，并传递至宿主植物为其所利用。由于这种养分传递的生态重要性，外生菌根真菌介导的“菌植”N传递关系受到研究人员的广泛关注。文中综述了外生菌根真菌的可利用N形式及其促进宿主植物N营养吸收的机理，主要归纳为:1）菌根增加了养分吸收面积，促进N吸收；2）外生菌根真菌编码利用N源所必需的一套酶和转运体，协助宿主对难吸收的硝酸盐和有机N的利用。在全球N沉降日益加剧的背景下，本综述将有助于了解外生菌根在当前和未来气候情景下的生态作用。

Nitrogen Uptake Promoting Mechanism of Trees in Ectomycorrhizal Symbioses

Ectomycorrhizal fungi can form a stable symbiont with certain trees, namely ectomycorrhiza. Ectomycorrhiza can absorb nutrients in inorganic or organic form in the soil that are hard to be absorbed by plants and transfer them to the host plants. Due to the ecological importance of this nutrient delivery, it is necessary to better understand the relationship of nitrogen delivery between fungi in ectomycorrhizal symbioses and host plants. This paper reviews the available nitrogen forms of ectomycorrhizal fungi and their mechanisms for promoting nitrogen uptake by host plants, which are summarized as follows: 1) Mycorrhizal colonization increases plant root nutrient uptake area and promotes N uptake; and 2) Ectomycorrhizal fungi encode a set of enzymes and transporters necessary for N source to assist the host plant in absorbing hard-to-use nitrate and organic nitrogen. This review can help better understand the ecological effects of ectomycorrhizal symbiosis in current and future climate scenarios under the background of increasing global nitrogen deposition.