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Authors:
Mexximiliaan M.S.F. Holweg, Thomas Curren, Aurora Cravino, Elias Kaiser, Iris F. Kappers, Ep Heuvelink, Leo F.M. Marcelis.
Affiliations: Wageningen University, Netherlands & Seoul National University, South Korea.
Practical Breakdown
The production of medical cannabis requires optimized environmental conditions to maximize the yield and consistency of plant specialized metabolites (PSMs), including cannabinoids and terpenoids. This study investigates the impact of air temperature and photosynthetic photon flux density (PPFD) on the accumulation of PSMs, inflorescence dry matter production, and photosynthetic efficiency in two cannabis genotypes: ‘Original Blitz’ (THC-dominant) and ‘Harmony CBD’ (CBD-dominant).
The experiment was conducted in climate-controlled chambers with three PPFD levels (600, 900, 1200 μmol m⁻² s⁻¹) during the short-day (flowering) phase and two air temperature regimes: low (25/21°C) and high (31/27°C). Plants were grown across four cultivation cycles, with nutrient conditions held constant. Data collection included destructive and non-destructive sampling to measure plant growth, metabolite concentrations, and photosynthesis.
Key Findings
Temperature Effects on PSMs: Higher air temperature (31/27°C) significantly reduced cannabinoid concentrations in both genotypes but did not affect terpenoid levels.
Inflorescence Development: High temperatures caused inflorescence abnormalities, including “fox-tailing,” disrupting maturation and leading to lower cannabinoid accumulation.
Dry Matter Production: Increased temperature had genotype-specific effects. ‘Original Blitz’ showed no significant change, while ‘Harmony CBD’ experienced reduced inflorescence and total plant dry matter production.
PPFD Effects on Yield: Increasing PPFD led to higher dry matter production and total cannabinoid yield in ‘Original Blitz’ but did not change cannabinoid concentrations. ‘Harmony CBD’ showed a similar trend, though the effects were less pronounced.
Photosynthetic Efficiency: Photosynthesis rates declined towards the end of the flowering phase due to leaf senescence, which was accelerated under high temperatures.
Application for Cultivators
Temperature Control is Critical: High temperatures (above 31°C) negatively impact cannabinoid accumulation and can lead to developmental abnormalities. Maintaining air temperatures at or below 25°C during the flowering phase is recommended.
Maximizing Light Exposure: Increasing PPFD up to 1200 μmol m⁻² s⁻¹ enhances biomass production and total cannabinoid yield, making it beneficial for commercial cultivation. However, care should be taken to balance light intensity with temperature control to prevent heat stress.
Leaf Senescence Management: The study suggests that adjusting light strategies based on plant maturity could improve light-use efficiency. Dynamic lighting approaches, rather than fixed PPFD throughout the growth cycle, may optimize photosynthesis and yield.
Genotype-Specific Responses: Different cannabis strains respond uniquely to environmental conditions. Cultivators should conduct genotype-specific trials to determine the optimal balance of temperature and light for their specific cultivars.
This study highlights the need for precise environmental control in medical cannabis production. By optimizing temperature and PPFD, cultivators can maximize both inflorescence dry matter production and cannabinoid yield while minimizing energy inputs.
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