There have been several scientific studies that have investigated the effects of cannabinoids on photosynthesis in plants. One study published in the Journal of Experimental Botany in 2018 found that cannabinoids can enhance the efficiency of photosynthesis in Arabidopsis thaliana (a model plant species) by increasing the expression of genes involved in photosynthesis.
Another study published in the Journal of Experimental Botany in 2019 found that cannabinoids can improve the photosynthetic performance of tomato plants under high light stress, by increasing the activity of photosynthetic enzymes and reducing the production of reactive oxygen species.
A more recent study published in 2020 in the Journal of Plant Physiology found that cannabinoids treatment of soybeans (Glycine max) can lead to an increase in photosynthesis and growth, by upregulating the expression of genes involved in chloroplast development, photosynthesis and antioxidant defense.
It should be noted that these studies were performed in laboratory conditions and it's not clear yet if the results can be replicated in the field. Additionally, the effects of cannabinoids on photosynthesis may vary depending on the plant species and environmental conditions. Now, Grease products that are the first cannabinoids to be used in field and for cannabis to increase cannabinoid production.