The use of biostimulants like humic substances is a promising innovative approach in agriculture to activate and sustain physiological plant processes. The development of specific bioassays is required to study their bioactivity in laboratory conditions. In previous investigations, a soil-less bioassay with cress seedlings (Lepidium sativum L.) was developed for a biostimulant used in the biodynamic agriculture, the horn-manure preparation (HMP), a fermented cow manure sprayed at low concentrations onto fields. Objectives of the present study were to refine the bioassay by investigating the interactions between the HMP bioactivity and the test factors (i) water volume, (ii) gravistimulation, and (iii) exposure to fluorescent light. The interactions between the test factors and the HMP treatment were significant in all series (p < 0.05, Wald F-test). Water overdose and gravitropic stress reduced root growth (down to − 24.2% and − 19.9%, respectively, p < 0.0001, Tukey–Kramer test). The HMP treatment partly compensated these effects by enhancing root growth by (i) water overdose (up to + 4.3%, p = 0.048, n = 4), and (ii) gravitropic stress (up to + 9.5%, p = 0.0004, n = 8). (iii) Furthermore, under the combined stress factors, fluorescent light exposure enhanced the HMP enhancing effect (up to + 12.3%, p = 0.007, n = 6). The HMP bioactivity appeared to consist of a compensatory mode of action regarding the stress factors water overdose and gravistimulation, and a synergetic interaction with fluorescent light exposure. The HMP seems to interact with the plant sensory systems, likely stimulating the plant’s adaptability to its environment by increasing self-regulating processes. The bioassay sensitivity was successfully increased by integrating these interactions in the experimental set-up and adjusting the growth environment. This approach can be used to adjust the bioassay to other biostimulants.

中文翻译：

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非生物因素和生物动力喇叭肥对独行菜的生长（生物活性之间的相互作用独行菜豌豆在生物测定L.）

诸如腐殖质之类的生物兴奋剂的使用是农业中激活和维持生理植物过程的一种有前途的创新方法。需要开发特定的生物检测方法来研究其在实验室条件下的生物活性。在以前的研究中，开发了一种无土生物测定法，其中有水芹苗（Lepidium sativum L.），用于生物动力农业中使用的生物刺激剂：牛角粪便制剂（HMP），这是一种低浓度喷洒到田间的发酵牛粪。本研究的目的是通过研究HMP生物活性与测试因子（i）水量，（ii）重力刺激和（iii）暴露于荧光灯之间的相互作用来完善生物测定。测试因子与HMP治疗之间的相互作用在所有系列中均显着（p <0.05，Wald F检验）。水过量和重力胁迫会降低根部生长（Tukey–Kramer试验，分别降至− 24.2％和− 19.9％，p <0.0001）。HMP处理通过（i）过量饮水（最高+ 4.3％，p = 0.048，n = 4）和（ii）重力应力（最高+ 9.5％，p = 0.0004， n = 8）。（iii）此外，在综合的压力因素下，荧光灯照射增强了HMP增强效果（高达+ 12.3％，p = 0.007，n = 6）。HMP的生物活性似乎包括关于水过量和去刺激的应激因素的补偿作用模式，以及与荧光暴露的协同作用。HMP似乎与植物的感觉系统相互作用，可能通过增加自我调节过程来刺激植物对环境的适应性。通过将这些相互作用整合到实验装置中并调节生长环境，成功提高了生物测定的灵敏度。该方法可用于将生物测定值调整为其他生物刺激剂。