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There are many biological processes that occur, mostly simultaneously, in a living plant. Some processes continue even after the cultivar is harvested like in the case of the [[Harvesting, Drying and Curing\|curing process]]. ~~==Gas exchange==~~ Plants draw in CO<sub>2</sub>, Oxygen, and water vapor from the air around them via the Stomata. These compounds are essential to other processes such as photosynthesis and Respiration. Airflow/wind speed has a strong effect on transpiration rate, gas exchange, and photosynthesis.<ref>https://doi.org/10.1016/S0273-1177(02)00747-0 - Effects of air current speed on gas exchange in plant leaves and plant canopies (2003)</ref> ==Photosynthesis== * Thrives where CO<sub>2</sub> concentration is > 200ppm (cannabis specifically thrives in >400ppm CO<sub>2</sub>) * Cannot survive in very hot environments * Loses 97% of water via transpiration Cannabis stands out from other plants for its tolerance to high light intensity. see [[Light#Ideal_light_conditions\|Ideal light conditions]] ==Respiration== Most plants are constantly respiring and cannabis is no exception. In the process of respiration, plants uptake CO<sub>2</sub> and expel Oxygen. CO<sub>2</sub> is essential to the process of photosynthesis. If a plant is exposed to less than 200ppm it will be unable to photosynthesize at all and will most likely die. Airflow or "wind speed" has a strong effect on the rates of respiration and transpiration.<ref>https://doi.org/10.1016/S0273-1177(02)00747-0 - Effects of air current speed on gas exchange in plant leaves and plant canopies (2003)</ref> The rate of respiration is directly correlated with the stomata density on growing leaves.<ref>John W. Kimball, 2020. Gas Exchange in Plants. Available at: https://bio.libretexts.org/@go/page/5785 [Accessed March 11, 2022].</ref> ~~In the dark plants respire instead of photosynthesizing. In this period they uptake Oxygen and expel Carbon dioxide via Gas exchange.~~ === Supplimenting additional CO<sub>2</sub> === In a city typical Co<sub>2</sub> levels are around 400-450ppm. This is acceptable for a growing plant but raising levels above 1000ppm can increase growth rates by up to 30%<ref>B. A. Kimball, 1983, Carbon Dioxide and Agricultural Yield: An Assemblage and Analysis of 430 Prior Observations - https://doi.org/10.2134/agronj1983.00021962007500050014x</ref> <ref>Hendrik Poorter, 1993, Interspecific Variation in the Growth-Response of Plants to An Elevated Ambient CO2 Concentration - http://dx.doi.org/10.1007/BF00048146</ref> when combined with sufficient light intensity by enabling higher rates of photosynthesis. For more on the limitation of low Co<sub>2</sub> at high levels of light intensity see: [[Light#Upper limit of light intensity\|Upper limit of light intensity.]] For more on how co<sub>2</sub> is applied in a grow setting see: [[Growing environments#Adding extra Co2\|Adding extra Co<sub>2.</sub>]] == Transpiration == The cultivar constantly moves water around internally via capillary action and releases water ~~vapour~~vapor into the environment through the stomata, this is the process of transpiration. The density of stomata and how open they are will determine the rate of transpiration. The [[Temperature and Humidity#VPD\|VPD]] of a plant's environment will affect its stomal response and in turn, its rate of transpiration. For higher VPD values rate of transpiration is generally higher up until a maximum threshold<ref>Plant responses to rising vapor pressure deficit, Grossiord 2020 - https://doi.org/10.1111/nph.16485</ref>. For Cannabis the maximum VPD is around 1.6kPa (Seedlings should be exposed to 0.4-0.8kPa until they are established). The rate of transpiration is also correlated to the light intensity the plant is being exposed to i.e. High light intensity equals a high rate of transpiration. ~~The~~Of course, the inverse correlation between humidity and rate of transpiration has been known since the 1930s.<ref>RELATIVE HUMIDITY VARIATIONS AFFECTING TRANSPIRATION, Hiram F. Thut 1938 -https://doi.org/10.1002/j.1537-2197.1938.tb09265.x</ref> Wind speed and CO<sub>2</sub> levels also ~~indicates~~cause a plant response that will affect the rate of ~~nutrient uptake~~transpiration. The rate of transpiration also affects the rate of water uptake through roots, this is because 97% of water Cannabis absorbs is lost via transpiration (this is a typical characteristic of a C3 plant). A higher water intake means that [[nutrients]] can be delivered more quickly. ==Circadian rhythm== Like animals, plants also have a Circadian rhythm, a sort of internal biological clock that is programmed by external stimuli. It has been shown that matching a plant's environment to its natural circadian rhythm can increase photosynthesis<ref>https://doi.org/10.1126%2Fscience.1115581 - Plant Circadian Clocks Increase Photosynthesis, Growth, Survival, and Competitive Advantage (2005)</ref><ref>https://doi.org/10.3389/fpls.2015.00245 - Interactions between circadian clocks and photosynthesis for the temporal and spatial coordination of metabolism (2015)</ref><ref>https://doi.org/10.1016/j.scienta.2014.03.014 - Leaf photosynthesis, plant growth, and carbohydrate accumulation of tomato under different photoperiods and diurnal temperature differences</ref> [http://www.plantcell.org/content/18/4/792 More on circadian rhythm in plants] [~~http://www.plantcell.org/content/18/4/792 More on circadian rhythm in plants]<ref>~~https://doi.org/10.1105/tpc.106.040980 Plant Circadian Rhythms - C. Robertson McClung April 2006~~</ref>~~] [https://www.researchgate.net/post/Is-there-any-report-on-circadian-rhythm-in-plants-grown-in-hydroponics/54e06adbd685cc12538b464d/citation/download Plant responses to circadian rhythm]