Effect of temperature on plant processes

1. Biochemical reactions:

a) Photosynthesis

• Rate of photosynthesis is reduced due to reduction in temperature.
• When maize plants are subjected to treatment of 10oC for 10 days, the rate of photosynthesis is also reduced by 33% of the untreated plants.
• At low temperature, leaves become yellow due to degradation of chlorophyll.
• Leaves emerge at shorter interval with increase in temperature.

b) Respiration

• Temperature strongly affects respiration within the range of 0-35oC.
• The rate of respiration increases about 2-4 times for each 10oC rise in temperature.
• With further increment in temperature upto 40oC the rate of respiration decreases. Enzymes begin to denature rapidly at higher temperature beyond 40oC.

c) Transpiration

• A rise in temperature brings about increase in the rate of transpiration.

d) Activities of growth substances

• At optimum temperature the activity of auxin, gibberellins and cytokinins (growth promoters)
• are high and activity of abscisic acid (growth regulator) is low with the result that growth rate is
• At high and low temperature, the balance of growth substances changes and affect growth.

2. Other effect of temperature on crop plants

i) Heat injury: High temperature accelerates the rate of transpiration causing desiccation which may result in temporary or permanent wilting.

ii) Cold injury: Cold temperature can injure plants, which depends upon the nature and condition of plants. Protoplasm freezes when the temperature drops below freezing point.

iii) Suffocation: The lack of O2 diffusion in the plant roots takes place due to covered of snow on the field, which causes suffocation of roots of plant. In this situation, ice in contact with roots inhibits diffusion of CO2 and respiratory products, which may become harmful to plants.