Semi‐polar root exudates in natural grassland communities

In the rhizosphere, plants are exposed to a multitude of different biotic and abiotic factors, to which they respond by exuding a wide range of secondary root metabolites. So far, it has been unknown to which degree root exudate composition is species-specific and is affected by land use, the local impact and local neighborhood under field conditions. In this study, root exudates of 10 common grassland species were analyzed, each five of forbs and grasses, in the German Biodiversity Exploratories using a combined phytometer and untargeted liquid chromatography-mass spectrometry (LC-MS) approach. Redundancy analysis and hierarchical clustering revealed a large set of semi-polar metabolites common to all species in addition to species-specific metabolites. Chemical richness and exudate composition revealed that forbs, such as Plantago lanceolata and Galium species, exuded more species-specific metabolites than grasses. Grasses instead were primarily affected by environmental conditions. In both forbs and grasses, plant functional traits had only a minor impact on plant root exudation patterns. Overall, our results demonstrate the feasibility of obtaining and untargeted profiling of semi-polar metabolites under field condition and allow a deeper view in the exudation of plants in a natural grassland community.

在根际（rhizosphere）生境中，植物会暴露于多种多样的生物与非生物因子，并通过分泌种类丰富的根系次生代谢物产生适应性响应。迄今为止，学界尚未明确根系分泌物的组成在多大程度上具有物种特异性，也不清楚其在田间条件下受土地利用方式、局部环境影响以及周边邻体群落的调控程度。本研究依托德国生物多样性探索计划（German Biodiversity Exploratories），采用植物生物测定法（phytometer）与非靶向液相色谱-质谱联用（LC-MS）相结合的分析方案，对10种常见草原植物的根系分泌物进行了分析，其中杂类草（forbs）与禾本科草本（grasses）各5种。冗余分析（redundancy analysis）与层级聚类（hierarchical clustering）结果显示，除物种特异性代谢物外，还存在一类广泛存在于所有受试物种的半极性代谢物（semi-polar metabolites）。化学多样性与分泌物组成分析表明，大车前草（Plantago lanceolata）、猪殃殃属（Galium）等杂类草分泌的物种特异性代谢物数量多于禾本科草本；而禾本科草本的根系分泌物组成则主要受环境条件调控。无论是杂类草还是禾本科草本，植物功能性状（plant functional traits）对其根系分泌模式的影响均较为有限。总体而言，本研究结果证实了在田间条件下开展半极性代谢物样本采集与非靶向谱分析的可行性，并为深入解析天然草原群落中植物的根系分泌过程提供了新的视角。