Photosynthesis and respiration
Photosynthesis and respiration are the two processes related to plant growth.
Photosynthesis:
CO2 + H2O ====> CH2O + O2
Respiration:
CH2O + O2 ====> CO2 + H2O+energy
Net production:
Gross assimilation - (respiration and reduction of assimilation by non-optimum temperatures).
Photosynthesis
In the photosynthesis process which takes place in green plant parts (mainly leaves) carbon dioxide in the leave tissue is bound to the chlorophyll and reduced to sucrose by absorption of light energy.
Light energy
The rate of photosynthesis on a certain day depends highly on the daylength and the light intensity (clouds or clear sky).
GROSS ASSIMILATION
Temperature
It is generally agreed that a temperature range of 20-25 °C is optimal for photosynthesis. Where the average day temperatures are about 30 °C and average night temperatures about 20 °C the net assimilation is about half of the assimilation rate at optimum temperatures.
Respiration
Respiration is divided in maintenance-respiration and growth-respiration. For
maintenance respiration
values of 20-25% are often found and for growth respiration values of 5-10%.
Respiration increases with increasing temperatures. Particularly above 30 °C, respiration increases rapidly resulting in a rapid decrease in net photosynthesis.
Tuber respiration
The heat produced by tuber respiration and the CO2 output during this process, are important factors to be considered in potato storage.
TUBER RESPIRATION
Carbon dioxide and water supply
The carbon dioxide used in the assimilation process can enter the leaves through the stomata when these are open. The stomata open if enough water is present in the plant (the plant is turgid) and the leaves are in full light. When the plant becomes dry the stomata close and the concentration of carbon dioxide rapidly falls below the optimum for maximum photosynthesis. A sound green crop and a good water supply form the bases for a high daily production of dry matter. A day without sufficient water for the crop is in fact a "lost day".
Light interception
Only the light intercepted by green leaves is used in the assimilation process. Parameters for light interception are: the amount of green plant parts present (percentage of soil coverage, LAI, crop density, etc.),.
Percentage ground cover
In a crop the percentage of the soil which is covered by green leaves can be estimated without damaging the crop. Percentage of soil cover is similar to what percentage of the incoming solar irradiation can be used for photosynthesis.
Ground coverage with green leaves---Ground coverage with green leaves
Leaf area index-LAI
For research purposes measurements of the LAI are made, but for such measurements plants have to be disturbed.
Leaf area index-LAI is the ratio of leaf surface over soil surface.
LEAF AREA INDEX