Browsing by Person "Reichel, Philipp-Severin Alfons"

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Lighting the Way: Disentangling the impact of light on yield, cannabinoids and terpenes in Cannabis sativa L.
(2024) Reichel, Philipp-Severin Alfons; Graeff-Hönninger, Simone
This thesis focuses on the evolving cultivation of C. sativa, which is rapidly changing due to increasing legalisation efforts. However, the main challenge is to bridge the gap between previously illegal knowledge and validated, accessible scientific evidence. There is still a notable lack of comprehensive government about the medicinal C. sativa sector, particularly with regard relation to the production of flowers. Knowledge of cultivation systems is proprietary. Scientific validation and stricter cultivation guidelines are urgently needed. Therefore, this thesis is dedicated to investigating the growth patterns of multiple C. sativa strains under different light spectra. The main objectives are to validate the efficacy of LED lighting systems, to determine the relationship between photosynthetic rates and flower yield, and to investigate the complex interactions in secondary metabolism. A major focus will be the investigation of changes in the heterogeneity of secondary metabolites and the development of strategies to mitigate this heterogeneity, emphasising the analysis of cannabinoids and terpenes. Ultimately, a comprehensive cultivation system will be established that demonstrates how light intensity, spectral composition, variety diversity, and plant density influence different flower positions within a C. sativa plant. This system will serve as a basis for the cultivation of medicinal C. sativa, bridging the gap between illegal practices and scientifically validated methods. The first step was to investigate parameters for optimising growth characteristics and secondary metabolite production in relation to specific strain characteristics by studying different C. sativa strains under different light spectra. Publication I addressed the following objectives: (1) to explore how different C. sativa strains adapt to various light spectra, studying growth patterns and overall morphology; (2) to investigate how distinct light spectra affect yield composition, revealing strain-specific responses to light exposure; and (3) to examine the influence of red to far-red light ratio on plant growth traits and biomass production. The publication Ⅰ involved three randomised light spectra (CHD, AP67 and SOL) and three different C. sativa strains (E19, A4 and KAN), each characterised by different growth habits. The primary objective was to estimate how these spectral variations affected plant morphology and yield. While most characteristics of the strains remained resilient to the effects of different light spectra, notable differences were observed in height and biomass distribution of main and side shoots. Plants grown under LED lamps showed a more compact growth pattern. Surprisingly, there were no discernible differences between light sources, spectra and C. sativa strains in total flower yield at 56 days after planting (DAP 56). However, changes in leaf fractions were observed as growth progressed, with sugar leaves emerging as a critical factor, particularly in the later stages of development. In the same experiment, the dried flower was divided into several flower positions to assess heterogeneity across the plant. These dried flowers from each strain were then analysed for cannabinoid and terpene composition. Detailed insights into these cannabinoid and terpene contents are provided in publication Ⅱ. The specific objectives of this thesis considered in this publication were (4) to study the impact of light spectra on the secondary metabolite development on different C. sativa strains and (5) to highlight the potential diversity of terpene and cannabinoid concentrations by identifying and comparing terpene profiles at different flower positions within each strain. Publication Ⅱ revealed a complex interaction between strain characteristics and light conditions, demonstrating that each strain retains its characteristic terpene profile regardless of light spectra. In particular, the research highlights the heterogeneity of secondary metabolites across different flower positions within the C. sativa plant, emphasising the critical role of light intensity and penetration in secondary metabolite production. Publication Ⅲ dealt with objective (6) to investigate how planting density affects individual yield, addressing competition dynamics among C. sativa to provide insights into optimal planting densities to maximise yield while considering space limitations and (7) to determine whether increased light intensity correlates with higher yields and concentrations of secondary metabolites. The main objective of publication Ⅲ was to understand the complex dynamics by which light-induced effects on individual plants can affect a high-density plant stock of 12 plants per m². The light intensity was increased from 680 PAR to 1200 PAR, a realistic level for C. sativa cultivation, and two experiments to achieve these objectives were conducted. The first experiment consisted of seven biomass sections to assess the influence of light on biomass distribution at a plant density of 2.66 plants per m². The results showed the potential of a low R: FR ratio to increase dry flower yield in the last ten days of flowering. The second experiment was designed to determine the impact of a light gradient on the distribution of secondary metabolites. Plant density remained constant throughout the experiment at 12 plants per m². The aim was to investigate if plant density correlated significantly with terpene and cannabinoid concentrations and if it induced variations in flower heterogeneity. The culmination of the findings from publications Ⅰ-Ⅲ and the ensuing discussion led to the development of an overall cultivation system consisting of three critical stages in the C. sativa growth cycle: 1) the vegetative phase under long-day conditions, 2) the initiation of flowers triggered by short-day photoperiods, and the subsequent biomass accumulation, culminating in 3) the ripening of flowers. The cultivation process begins with selecting a high-performance strain and producing healthy cuttings by propagation or hybrid seed. Rooted young plants are then placed in a suitable medium for the vegetative growth phase (stage one), characterised by long-day conditions (18:6). During this phase, the emphasis is on rapid development and biomass accumulation. In contrast, the plant structure is shaped by pruning. We recommend light defoliation of at least 20% and removal of lower lateral shoots. A gradual increase in light intensity from 400 to 950 PAR with an emphasis on 750 PAR is beneficial. Effective light spectra include SOL, AP67 and CHD, with 19%, 12% and 16% blue, respectively. Ideal conditions include CO2 levels of 900 ppm and temperatures around 25°C. In stage two (flowering), higher light levels and adapted fertilisation become important. Increased light intensity, especially at levels such as 1500 - 2000 PAR with 900 ppm CO2, will increase yield and potentially secondary metabolite production. Light spectra with a high share of green light around 510 nm and with an elevated green content can be beneficial under high intensities and densities. Controlled dimming strategies help maintain uniform light distribution, which is essential for homogenous terpene concentrations. Fertilisation should be dynamic with nitrogen concentrations below 240 mg N l-1 to avoid oxidative stress. In stage three (ripening), increasing FR (far red) can increase flower yield, making dynamic spectrum management valuable. Fertigation should be adjusted as biomass growth plateaus, gradually reducing nutrient levels in the final four weeks. At the same time, increasing the CO2 concentration to 1150 ppm at these lower N levels can benefit the final yield and secondary metabolite concentration. For this cultivation system to be successful, the fundamentals of precise environmental control, diverse strain selection and stable genetics are essential for medicinal C. sativa cultivation. Critical factors for cultivation include light intensity, distribution and penetration, and appropriate fertilisation. In addition, light uniformity and illumination within the canopy are essential for terpene standardisation. Pruning techniques and fertilisation should be adapted to the plant's growth stage. In summary, this thesis explores the dynamic field of C. sativa cultivation driven by legalisation. Recognising the key role of light in shaping successful cultivation techniques, this thesis contributes to a more comprehensive understanding of medicinal C. sativa cultivation.