Questo è solo un mito che alcune piante producono ossigeno di notte o svolgono la fotosintesi anche durante la notte. Lo stesso caso è con il tulsi (basilico). Proprio come le piante normali, il tulsi fa la fotosintesi (cioè assume CO2 ed espira O2) durante il giorno e la respirazione (cioè assume O2 ed espira CO2) durante la notte.

Forse è l'enorme valore medicinale e sacro per cui la gente ha creato queste idee sbagliate.

Tulsi Plant does not produce oxygen in night time.

As per some of the other answers given that it does and the reason is CAM (Crassulasian Acid Metabolism), they are wrong on both accounts.

1. Tulsi is not a plant that undergoes CAM. Not enough study has been conducted to conclude Tulsi undergoes CAM even in certain conditions. CAM is a carbon fixation pathway that evolved in some plants as an adaptation to arid conditions. Tulsi is not a plant that grows in arid conditions (Try not watering your tulsi plant for a day or two).
2. Even plants that undergoes CAM do not produce oxygen in night time. In a plant using full CAM, the stomata (little holes on the back side of a leaf) in the leaves remain shut during the day to reduce evapotranspiration, but open at night to collect carbon dioxide (CO2). These CO2 are stored inside the leaves and is utilised during daytime for photosynthesis without opening it's stomata. No Oxygen is released when the plant is absorbing CO2 in the night, as no photosynthesis takes place in absence of light.

References:

1. Ranson S. L., Thomas M (1960). Crassulacean acid metabolism. Annual Review of Plant Physiology. 11 (1): 81–110
2. Smith, J. A. C., & Winter, K (1996): Taxonomic distribution of Crassulacean acid metabolism. In K. Winter & J. A. C. Smith (Eds), Crassulacean Acid Metabolism: Biochemistry, Ecophysiology and Evolution (pp 427–36). Springer-Verlag Berlin Heidelberg.