Institut für Kulturpflanzenwissenschaften

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Impacts of different light spectra on CBD, CBDA and terpene concentrations in relation to the flower positions of different cannabis Sativa L. strains
(2022) Reichel, Philipp; Munz, Sebastian; Hartung, Jens; Kotiranta, Stiina; Graeff-Hönninger, Simone
Cannabis is one of the oldest cultivated plants, but plant breeding and cultivation are restricted by country-specific regulations. The plant has gained interest due to its medically important secondary metabolites, cannabinoids and terpenes. Besides biotic and abiotic stress factors, secondary metabolism can be manipulated by changing light quality and intensity. In this study, three morphologically different cannabis strains were grown in a greenhouse experiment under three different light spectra with three real light repetitions. The chosen light sources were as follows: a CHD Agro 400 ceramic metal-halide lamp with a sun-like broad spectrum and an R:FR ratio of 2.8, and two LED lamps, a Solray (SOL) and an AP67, with R:FR ratios of 13.49 and 4, respectively. The results of the study indicated that the considered light spectra significantly influenced CBDA and terpene concentrations in the plants. In addition to the different light spectra, the distributions of secondary metabolites were influenced by flower positions. The distributions varied between strains and indicated interactions between morphology and the chosen light spectra. Thus, the results demonstrate that secondary metabolism can be artificially manipulated by the choice of light spectrum, illuminant and intensity. Furthermore, the data imply that, besides the cannabis strain selected, flower position can have an impact on the medicinal potencies and concentrations of secondary metabolites.
Practicing the pot culture: pursuing sustainable agronomic management techniques for indoor medicinal cannabis cultivation
(2025) Massuela, Danilo Crispim; Graeff-Hönninger, Simone
With the legalization of cannabis cultivation in Germany, the country took an important step into becoming one of the major economies to legalize the cultivation of cannabis for personal use in the EU. In addition, the demand for cannabis products in different sectors is constantly increasing, and further rapid growth is forecasted. The institutionalization and representation of cannabis cultivation in the scientific literature are paramount to enabling efficient, secure, sustainable, and equitable good cultivation practices in the German cannabis industry and governmental decision-making processes. While exploring the potential of medicinal cannabis production, there is also the necessity to cultivate significant amounts of inflorescences to supply this craving demand. Indoor cultivation systems are the preferred method. The system is characterized by the highest degree of control over environmental variables of light (intensity, spectrum, duration), carbon dioxide concentration, temperature, air (humidity and distribution), water and nutrients (irrigation regimes and fertilizer – composition and concentration), and management techniques. Besides the mentioned advantages above, these systems are discussed to be the most unsustainable form of cannabis cultivation, with a high carbon footprint, energy demand, and resource utilization. Considering the absence of peer-reviewed scientific information in the cannabis industry, many businesses rely on management techniques from non-peer-reviewed sources, like commercial datasheets or gray literature. Much of the research in this field is conducted privately by companies in the cannabis industry. This thesis aims to contribute to the scientific knowledge of cannabis cultivation. The primary objective of this thesis was to investigate the production of medicinal cannabis in indoor cultivation systems. The specific focus was on applying agronomic management techniques to optimize yield components of medicinal cannabis. More precisely, emphasis was given to the balancing act of inflorescence biomass accumulation and the concentration of CBD in the inflorescences over time under abiotic stress induction, such as pruning, nutrient, and water deprivation. The effect of each tested agronomic management technique on yield components is presented in publications Ⅰ-Ⅲ. Publication I investigated the optimum harvest time and canopy management based on the total accumulated CBD yield. The findings highlighted that nine weeks of flowering was considered the optimum harvesting time for the tested genotype, as no significant enhancement in CBD yield was found after that. Additionally, it was demonstrated that pruning techniques can modify plant architecture and growth, leading to different inflorescence allocations in plant height. Inflorescences at the top position have significantly higher CBD concentrations. Thus, applying pruning techniques like topping can enhance CBD yield due to optimized canopy formation and area utilization in indoor cultivation systems. Publication II examined the impact of induced nutrient deprivation on plant biomass and CBD yields and the nutrient use efficiency of N, P, and K for three fertilizer concentrations of organic and mineral fertilizers. The results highlighted the dynamics of nutrient accumulation and re-mobilization among plant organs over time and the efficiency of nutrient utilization when plants are exposed to nutrient deprivation during flowering. Finally, inducing nutrient stress at the flowering stage could increase plant nutrient use efficiency and reduce fertilizer inputs without penalizing yields. The re-mobilization of already acquired nutrients presents this compensation. Publication III evaluated drought stress treatments' influence on CBD concentration and plant biomass production. As water and irrigation techniques are of paramount agronomical importance, the impact of moderate and severe drought treatments for two high-CBD genotypes with significantly different growth characteristics and water demands was tested. The drought events occurred at three phenological stages of inflorescence formation and maturation. Results highlighted different genotypic reactions and the adverse effects of applying severe stresses, significantly affecting photosynthesis, respiration, and plant water status. On the other hand, applying moderate stress can enhance water use efficiency by reducing water inputs without penalizing yield. Furthermore, the findings of this work showed that harvesting at the optimum time, pruning plants, and inducing moderate nutrient and drought stress during the flowering stage could be beneficial to enhance CBD yields while reducing resource input and increasing time, space, fertilizer, and water use efficiency. Overall, this thesis provided a broad dataset and findings that can support growers in investigating the effect of interventions on yield components, the effectiveness of agronomic management techniques like improved canopy and root zone management, and the effects of abiotic stresses on the overall optimization of cultivation systems. This thesis further expands on the critical questioning of the sustainability of indoor systems, highlighting major environmental issues of cultivation, such as the high amounts of energy and water utilization, waste generation, air pollution, and GHG emissions. This led to the reflection on alternative cultivation systems to supply the growing demand for medicinal cannabis in Germany. It is worth saying that indoor cultivation is possibly still the best system to provide medical – GACP/GMP pharmaceutical grade – cannabis due to the high level of environmental control, safety, and contamination protection. Nonetheless, there is still much to be improved in those systems, and future developments should aim either at (I) “high-tech” systems with efficient lights, soilless hydroponics or DWC under closed water and nutrient cycles, improved sensors and automation systems for less human interaction to avoid contamination and minimum energy and resources deployment. Future systems should possibly include the verticalization of cultivation areas and the use of AI to guarantee fewer variations in climate conditions and, therefore, higher standardization of inflorescences in production batches and/or (II) a shift towards “soil-sun grown” cannabis and protected environment production, especially using greenhouse and tunnels in outdoor conditions. As demonstrated, those systems have higher yield potential and improved sustainability of cultivation while using the sun as a primary energy source and the soil as the basis for cultivation. At the same time, regenerative practices would be the preferred form of soil fertility management, organic nutrient cycling, and crop nutrition. It is essential to note those systems' limitations in acquiring pharmaceutical-grade certification of medical inflorescences. However, inflorescences per se might not be the best medical product as the standardization of cannabinoid concentration in inflorescences is challenging and subject to natural variation. Nonetheless, “soil-sun grown” can be a primary significant cultivation system to produce medicinal cannabis – cannabis plants that can be used for medicinal purposes – as practiced for most medicinal plants and other crops of medicinal value (herbs, teas, essential oils). These systems can be scaled up more easily than indoor cultivation and can yield large harvests to provide inflorescences and biomass to extract cannabinoids, terpenes, flavonoids, etc., which can later be used to generate medical products. Observing the experience of other countries, it is expected that a tremendous demand for cannabis in Germany will not be medical pharmaceutical inflorescences from the pharmacy (as before the legalization) but rather medicinal/recreational inflorescences from individuals, cultivation clubs, and model projects. In summary, this thesis explores the dynamic field of cannabis cultivation driven by societal demands and recognizes the crucial role of adapting cultivation systems to market needs. As suggested in the discussion, categorizing medical and medicinal cannabis products is necessary to fit cultivation systems to meet consumer demand. Furthermore, the moment permits historical reparation and the insertion of marginalized groups in a transformative landscape of cannabis cultivation. If we want to pursue socially equitable cannabis, we cannot simply ignore what has been done to smallholder farmers in traditional cannabis-producing regions through the war on drugs. Enabling the import of cannabis inflorescences and extracts from regions under ecologically and socially sustainable cultivation practices with certification labels can be a milestone in promoting fairer agricultural trades, providing legal livelihood opportunities, and developing strong value chains, like other delicacies such as tea and spices, cocoa, and coffee. Thus, certified imports from traditional producers can be vital, given the global climate and energy crisis challenges.

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