Tree species rather than type of mycorrhizal association drives inorganic and organic nitrogen acquisition in tree-tree interactions

A field study was conducted to evaluate the effects of associated mycorrhization type on tree-tree interactions using the framework of the MyDiv tree diversity experiment established at the Bad Lauchstädt Experimental Research Station of the Helmholtz Centre for Environmental Research (UFZ) (Saxony-Anhalt, Germany). Inorganic and organic net N uptake capacity was quantified in fine roots of AM (i.e. Acer pseudoplatanus L., Fraxinus excelsior L., and Prunus avium L.) as well as EM associated tree species (i.e. Carpinus betulus L., Fagus sylvatica L., and Tilia platyphyllos Scop.) using 15N/13C isotopes. Trees grew either in monocultures or 2-species mixtures, either only ectomycorrhizal, only arbuscular mycorrhizal, or in combination. Generally, ammonium was preferred over glutamine and glutamine over nitrate. Inorganic and organic N sources were not used complementarily depending on a species´ mycorrhizal association, but their uptake rather depended on the competitor indicating species-specific effects. At the species level, inorganic and organic N acquisition differed among the studied tree species. N acquisition within tree species changed N source-specific depending on the competitor.

Methods
see publication in Tree Physiology for full description of methods

本研究依托亥姆霍兹环境研究中心（Helmholtz Centre for Environmental Research, UFZ）巴劳赫斯塔特实验研究站（位于德国萨克森-安哈尔特州）搭建的MyDiv树木多样性实验框架，开展野外实地研究，旨在评估菌根共生类型对树木间相互作用的影响。本研究采用¹⁵N/¹³C同位素示踪技术，量化了丛枝菌根（Arbuscular Mycorrhizal, AM）共生树种（即假挪威槭*Acer pseudoplatanus* L.、欧洲白蜡*Fraxinus excelsior* L.与欧洲甜樱桃*Prunus avium* L.）以及外生菌根（Ectomycorrhizal, EM）共生树种（即欧洲鹅耳枥*Carpinus betulus* L.、欧洲山毛榉*Fagus sylvatica* L.与阔叶椴*Tilia platyphyllos* Scop.）的细根对无机态与有机态氮的净吸收能力。供试树木以单优群落或两物种混交群落的模式种植，群落配置分为仅含外生菌根共生树种、仅含丛枝菌根共生树种，以及二者混合配置三种类型。整体来看，树木对铵态氮的吸收偏好显著高于谷氨酰胺，对谷氨酰胺的吸收偏好又高于硝酸盐。研究未发现基于树种菌根共生类型的无机与有机氮源互补利用现象，氮源吸收反而受共存竞争者的调控，体现出物种特异性效应。在物种水平上，供试树种间的无机与有机氮获取策略存在显著差异；同一树种的氮获取模式，会因共存竞争者的不同而随氮源类型发生改变。

方法
详见发表于《Tree Physiology》的论文以获取完整方法描述。