An Evaluation of the Growing Environment on the Production of Secondary Metabolites in Cannabis Plants

By Scott Churchill, Vice President of Scientific Operations at MCR Labs

Introduction / Hypothesis

Cannabis can be grown in multiple environments, and each environment has its own set of benefits and disadvantages depending upon the end goal of the grower. The question asked in this experiment is whether clones sharing the same genetic information express different secondary metabolites as a function of the environmental conditions they are grown in.

Variables

The main variables in this experiment relate directly to the growing environment, indoor or outdoor. However, there are also other variables in addition to the environment that may impact compound production that we need to be aware of such as genetics, nutrition, and lighting.

While using clones enables us to focus on holding genetic variables constant, it is important to consider that some specific strains have been bred over time to consistently produce certain metabolites, such as 1:1 CBD/THC strains.

Nutrient and irrigation techniques also play a major role. In indoor growing environments you have much more control when it comes to watering schedule and nutritional uptake, while when growing outdoors you may have soil with its own nutrition, ground water, and variable rain in addition to your watering and feeding regimen.

Lighting is also a major variable. Outdoor growing environments can take full advantage of the sun’s full spectrum and intensity, but a cultivator needs to consider the movement of the sun throughout the day. Indoor cultivation has the advantage of controlling the duration and intensity of light. However, it is very difficult to mimic the full spectrum light from the sun.

Results

Overall findings show trends in higher secondary metabolites in samples grown outdoors which signifies that a more dynamic environment will induce more responses from the plant. There were also a greater number of larger, more oxygenated and sugar-conjugated species vs. lighter, less oxygenated species such a linalool, terpinolene, and borneol. This indicates that not only is there more of a response from this environment, but the response also becomes more complex and specialized.

We also observed strain-specific data that represents genetics overcoming the difference between indoor and outdoor. Two strains were found to be more impacted by genetics than by environmental conditions and showed less of a difference between indoor and outdoor than strain to strain.

We also had limited data that showed heavy metal trends. Two of the four clones were tested for heavy metals, and both showed a response for cadmium in the indoor whereas the outdoor did not.

Discussion

The targeted approach confirmed that secondary metabolites were elevated in samples grown outdoors. The limited data that we have for heavy metals data shows there is something different in the environment that results in the plant having more heavy metals in their tissues in the indoor growing environment than the outdoor. Genetics were controlled by using clones but better control over nutrition and watering is needed.

In the untargeted approach indoor and outdoor are primarily separated by PC2. Some strains are unique in that they stand up to the different environment and stay true to their genetics while others are more heavily influenced by the conditions. The types of natural products observed elevated at the different growing conditions are delineated by the examples shown such as the lighter and simpler compounds like terpenes versus the heavier flavonoid molecules expressed by the outdoor plants.

Conclusion

The cultivation method impacts both the amount and type of secondary metabolites produced. These results have implications when you are choosing growing conditions. You not only think about the costs and environmental impact or the regulatory environment, but also consider what kind of molecules of interest and therapeutic molecules you wish to express in your plants. Further work is needed to identify which environmental conditions turn on the plant’s ability to make the more complex compounds that are of therapeutic interest.