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The results of these experiments have shown that the crops do not thrive as well in this environment. Plants do need CO2, but they also need water, nitrogen, and other nutrients. Some do not grow much more at all. Others, like wheat, grow bigger but end up with less nitrogen. As a result, insects end up eating more to get the nitrogen they need.
The nutritional value of food plants would be similarly reduced for other animals — including humans. Also, we could end up with vegetables that have too much carbon — perhaps producing spinach that would be very tough to chew! Researching and reporting the science and impacts of climate change. Who We Are An independent organization of leading scientists and journalists researching and reporting the facts about our changing climate and its impact on the public.
With the development of improved lighting systems, environmental controls and balanced nutrients, the amount of CO 2 is the only limiting factor for maximum growth of plants. Thus, keeping the other growing conditions ideal, supplemental CO 2 can provide improved plant growth.
Timing, duration and concentration determines the efficiency of CO 2 supplementation. Carbon dioxide supplementation is not required if all the growing conditions are ideal and the rate of growth is satisfactory to the grower. However, if plants do not meet the required growth, mostly in the fall through early spring, supplemental CO 2 is beneficial. At that time of the year, the vents are closed most of the time, limiting available CO 2. Adding CO 2 one to two hours after sunrise and stopping two to three hours before sunset is the ideal duration of supplementation.
Plants are photosynthetically active one to two hours after sunrise reaching peak at to p. However, leafy greens and vegetables in a hydroponic system can be supplemented with CO 2 and a grow-lighting system 24 hours a day. Seedlings supplemented with CO 2 in flats will be ready to transplant one or two weeks earlier.
Supplementing CO 2 at an early age reduces the number of days to maturity and plants can be harvested earlier. Young plants are more responsive to supplemental CO 2 than more mature plants. The rate of photosynthesis cannot be increased further after certain intensity of light termed as the light saturation point, which is the maximum amount of light a plant can use. However, additional CO 2 increases the light intensity required to obtain the light saturation point, thus increasing the rate of photosynthesis.
Mostly in the winter, photosynthesis is limited by low light intensity. An additional lighting system will enhance the efficiency of CO 2 and increase the rate of photosynthesis and plant growth. Thus, supplemental CO 2 integrated with supplemental lighting can decrease the number of days required for crop production.
Supplemental CO 2 affects the physiology of plants through stomatal regulation. Elevated CO 2 promotes the partial closure of stomatal cells and reduces stomatal conductance. Stomatal conductance refers to the rate of CO 2 entering and exiting with water vapor from the stomatal cell of a leaf.
Because of reduced stomatal conductance, transpiration loss of water from leaf stomata in the form of water vapor is minimized and results in an increased water use efficiency WUE ratio of water used in plant metabolism to water lost through transpiration. Lower stomatal conductance, reduced transpiration, increased photosynthesis and an increase in WUE helps plants to perform more efficiently in water-stressed conditions.
Supplemental CO 2 reduces water demand and conserves water in water-scarce conditions. Temperature plays a big role in the rate of plant growth. Most biological processes increase with increasing temperature and this includes the rate of photosynthesis.
But the optimum temperature for maximum photosynthesis depends on the availability of CO 2. The higher the amount of available CO 2 , the higher the optimum temperature requirement of crops Figure 2. In a greenhouse supplemented with CO 2 , a dramatic increase in the growth of plants can be observed with increasing temperature. Supplemental CO 2 increases the optimum temperature requirement of a crop. This increases production even at higher temperature, which is not possible at the ambient CO 2 level.
Figure 2. Relationship between leaf temperature and net photosynthetic rate at ambient and CO 2 elevated condition in Populas grandidentata Jurik et al. A major effect of CO 2 supplementation is the rapid growth of plants because of enhanced root and shoot growth. The enhanced root system allows greater uptake of nutrients from the soil.
It is recommended to increase fertilizer rate with increasing CO 2 level. The normal fertilizer rate can be exhausted quickly and plants may show several nutrient deficiency symptoms. Although strict recommendations of nutrients for different crops at different levels of CO 2 are not presently available, in general nutrient requirements increase with increasing levels of CO 2.
On the other hand, some micro nutrients are depleted quicker than macro nutrients. Some studies have reported low levels of zinc and iron in crops produced at higher CO 2 levels. Further decrease in transpiration and conductance with CO 2 supplementation may affect calcium and boron uptake, which should be compensated through addition of nutrients.
Carbon dioxide is a free gas present in the atmosphere. Carbon dioxide should be supplemented in a pure form. A mixture of carbon monoxide, ozone, nitrogen oxides, ethylene and sulfur impurities in some CO 2 sources may damage the plant.
Carbon monoxide should not exceed 50 parts per million; otherwise CO 2 supplementation will be harmful rather than beneficial. There are different methods of CO 2 supplementation and the principle of CO 2 production is different depending on the method selected.
Some of the methods are discussed below. Since CO 2 is a free and heavy gas, it stays at a lower level in the greenhouse. Carbon dioxide produced by plants at night is depleted within a few hours after sunrise, thus proper ventilation integrated with horizontal airflow fans just above the plant can help in distributing available CO 2 at least to the ambient level. It is the cheapest method for maintaining an ambient level of CO 2.
But in winter, the extreme climatic conditions do not favor this method and additional CO 2 sources are required. Another natural way of increasing CO 2 in the greenhouse is through human respiration. Humans also exhale CO 2 during respiration like plants. People working in the greenhouse for pruning, irrigation and other operations can increase CO 2 levels. Using compressed CO 2 is a popular method of CO 2 enrichment. The CO 2 is in a compressed liquid form and vaporizes through use of CO 2 vaporizer and is distributed through a distribution system.
Holes are added to poly vinyl chloride PVC pipes and spread throughout the greenhouse for even distribution in larger operations.
However, CO 2 is released directly from a tank in small greenhouses.
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