Heuermann Diana, Döll Stefanie, Schweneker Dörte, Feuerstein Ulf, Gentsch Norman, von Wirén Nicolaus
Physiology and Cell Biology, Leibniz Institute of Plant Genetics and Crop Plant Research Gatersleben, Seeland, Germany.
Stress and Developmental Biology, Leibniz Institute of Plant Biochemistry, Halle (Saale), Germany.
Front Plant Sci. 2023 Apr 6;14:1122285. doi: 10.3389/fpls.2023.1122285. eCollection 2023.
Plants release a large variety of metabolites via their roots to shape physico-chemical soil properties and biological processes in the rhizosphere. While hydroponic growth conditions facilitate accessibility of the root system and recovery of root exudates, the natural soil environment can alter root metabolism and exudate secretion, raising the question to what extent the quantity and composition of root exudates released in hydroponic growth systems reflect those recovered from soil-grown roots.
Using a root washing method, we sampled root exudates from four field-grown cover crop species with wide taxonomic distance, namely white mustard, lacy phacelia, bristle oat, and Egyptian clover. A set of primary metabolites and secondary metabolites were analysed in a targeted and untargeted LC-MS-based approach, respectively, for comparison with exudates obtained from hydroponically cultured plants.
We found that hydroponically cultivated plants released a larger amount of total carbon, but that the recovery of total carbon was not indicative for the diversity of metabolites in root exudates. In the field, root exudates from phacelia and clover contained 2.4 to 3.8 times more secondary metabolites, whereas carbon exudation in hydroponics was 5- to 4-fold higher. The composition of the set of metabolites identified using the untargeted approach was much more distinct among all species and growth conditions than that of quantified primary metabolites. Among secondary metabolite classes, the presence of lipids and lipid-like molecules was highly indicative for field samples, while the release of a large amount of phenylpropanoids, organoheterocyclic compounds or benzenoids was characteristic for clover, mustard or oat, respectively, irrespective of the cultivation condition. However, at the compound level the bulk of released metabolites was specific for cultivation conditions in every species, which implies that hydroponically sampled root exudates poorly reflect the metabolic complexity of root exudates recovered from field-grown plants.
植物通过根系释放出大量的代谢产物，以塑造根际土壤的物理化学性质和生物过程。虽然水培生长条件便于根系接触和收集根系分泌物，但自然土壤环境会改变根系代谢和分泌物分泌，这就引发了一个问题，即水培生长系统中释放的根系分泌物的数量和组成在多大程度上反映了从土壤种植根系中回收的分泌物。
我们采用根系冲洗法，从四种分类距离较远的田间种植覆盖作物物种（即白芥、蕾丝花、硬毛燕麦和埃及三叶草）中采集根系分泌物。分别采用基于液相色谱-质谱联用（LC-MS）的靶向和非靶向方法分析了一组初级代谢产物和次级代谢产物，以便与水培植物获得的分泌物进行比较。
我们发现，水培植物释放的总碳量更多，但总碳的回收量并不能指示根系分泌物中代谢产物的多样性。在田间，蕾丝花和三叶草的根系分泌物中次级代谢产物含量高出2.4至3.8倍，而水培条件下的碳分泌量则高出5至4倍。使用非靶向方法鉴定的代谢产物组的组成在所有物种和生长条件下比定量的初级代谢产物更为不同。在次级代谢产物类别中，脂质和类脂质分子的存在对田间样本具有高度指示性，而大量苯丙烷类化合物、有机杂环化合物或苯类化合物的释放分别是三叶草、芥菜或燕麦的特征，与种植条件无关。然而，在化合物水平上，每个物种释放的大部分代谢产物都特定于种植条件，这意味着水培采样的根系分泌物很难反映从田间种植植物中回收的根系分泌物的代谢复杂性。
