The process of respiration in plants involves using the sugars produced during photosynthesis plus oxygen to produce energy for plant growth. In many ways, respiration is the opposite of photosynthesis. In the natural environment, plants produce their own food to survive.
They use the carbon dioxide (CO2) from the environment to produce sugars and oxygen (O2), which can later be utilized as a source of energy. While photosynthesis takes place in the leaves and stems only, respiration occurs in the leaves, stems and roots of the plant. The process of respiration is represented as follows:
C6H12O6 + 6O2 → 6CO2 + 6H2O + 32 ATP (energy)
Respiration takes place in all plant cells but can only use one source of fuel and that is the glucose or starch already produced by photosynthesis. This means that Photosynthesis and Respiration are locked into a kind of race. As Respiration fuels growth it is said to assimilate the products of photosynthesis i.e. assimilate the food into plant tissue. This means that for good steady plant growth, photosynthesis must produce more food than respiration requires. The measurement of this is called the Net Assimilation Rate (NAR). When photosynthesis can’t keep up with respiration, growth and repair will slow down or even stop.
As with photosynthesis, plants get oxygen from the air through the stomata. Respiration takes place in the mitochondria of the cell in the presence of oxygen, which is called “aerobic respiration”. In plants, there are two types of respiration: dark respiration and photorespiration. The first kind occurs in the presence or absence of light, while the second occurs exclusively in the presence of light. Respiration operates continually even at night and of course Photosynthesis only happens in sunlight. Both processes require a suitable temperature to work also. This explains the slow down of growth in the cooler, darker months. It also explains the need for different turf management practices where there is shade.
Role of air temperature: Plant respiration occurs 24 hours per day, but night respiration is more evident since the photosynthesis process ceases. During the night, it is very important that the temperature is cooler than during the day because plants can experience stress. Imagine a runner in a marathon. The runner respires at higher rates than a person standing still; therefore, a runner’s rate of respiration is higher and the temperature of the body increases. The same principle applies to plants, as temperature at night increases, the respiration rate increases and consequently temperature increases. This action could result in flower damage and poor plant growth.
Roots need oxygen: One of the functions of the substrate is to serve as a site for air exchange between the root zone and atmosphere. In other words, roots breathe oxygen like we do. Different plants have different oxygen requirements for their root systems. For example, the root system of a poinsettia requires a lot of oxygen, so it is best to use a substrate with high air porosity, while hostas can live well in a substrate with a high water holding capacity. A defense mechanism for plants under waterlogged or excessively dry conditions is to grow aerial roots from the stem just above the root crown; however, the ambient relative humidity must be high to sustain root growth outside the substrate.