Balancing Photosynthesis and Respiration
To maximize plant growth and yield, growers need to promote the correct balance between photosynthesis and respiration. Photosynthesis only happens in the light. Light energy is absorbed by chlorophyll and other pigments, and the energy is shuttled to reaction centres to manufacture sugars for energy storage. Growers can help maximize photosynthesis by providing their plants with plenty of full spectrum light and increasing the levels of carbon dioxide in the air. Warmer temperatures also increase photosynthesis. But temperature extremes should be avoided. Heat stress can cause the plant to stop performing normal photosynthesis, reducing its ability to store energy.
Respiration happens both day and night
In the presence of oxygen and metabolic enzymes, some of the stored sugars produced through photosynthesis are used as fuel to provide the energy needed for growth and reproduction. This process is known as cellular metabolism. Since oxygen is necessary for the process, growers can help increase the metabolism of their plants by providing plenty of dissolved oxygen at the root zone. So avoid over watering in soil, and oxygenate the water in hydroponics.
Temperatures also affect Metabolism
Too cold, and root metabolism ceases. Too warm, and the water can’t hold enough dissolved oxygen, limiting metabolism and setting up conditions for root rot. So the ideal water temperature for root metabolism is between 68-75° F.
Air temperature is also important for balancing photosynthesis and metabolism, especially the difference between day and night temperatures. The greater the difference between day and night temperature, the more the plant stretches. Growers should try to make sure that there is no more than about a 10° difference between day temperature and night temperature. Stretching is a waste of space and an inefficient use of the plant’s energy. In fact, computer-controlled greenhouses often have photo-sensors that measure accumulated sunlight during the day. As light levels increase, more carbon dioxide is added to the air to increase photosynthesis. The computer also measures the total amount of accumulated sunlight during the day, and adjusts the night-time temperatures according to how much light energy the plants received the previous day. Photosynthesis minus respiration equals growth!
Adjust Nutrient Solution
Adjustments can also be made to the nutrient solution to help balance photosynthesis and respiration. For example, raising the EC of the nutrient solution restricts vegetative growth, and lowering the EC of the nutrient solution promotes vegetative growth. Trace elements are also essential for photosynthesis and metabolism, especially iron, copper and manganese. Metals contribute to the electron transport chain for energy transfer. So adding organic chelators such as amino acids, humic acid and fulvic acid can have a dramatic effect on the balance between photosynthesis and respiration.
B-vitamins are also critical to cellular metabolism, both for plant cells and beneficial microorganisms. The engine of the plant cell is driven by a series of enzymes in the Krebs cycle. Some of those enzymes are inactive unless turned on by specific co-factors. B-vitamin derivatives form the co-factors that turn on many of these key enzymes, allowing cellular metabolism to function at full capacity. Since B-vitamins function at the microscopic level, it only takes a little to have a positive effect on the plant.
Other organic bio-stimulants can also have a dramatic effect on photosynthesis and respiration. For example, amino acid blends increase chlorophyll production, and the combination of seaweed extracts and humic acids stimulate the production of plant-protection enzyme called superoxide dismutase. During accelerated photosynthesis and metabolism, superoxide free radicals are generated that can damage cell membranes, chloroplast membranes and mitochondrial membranes. But superoxide dismutase breaks the damaging free radicals and protects the power generator of the plant. So to preserve the balance of power between photosynthesis and respiration, organic bio-stimulants are more important than ever!
Harley N. Smith