Get complete information on Crassulacean Acid Metabolism (CAM)

i. Takes place in succulents (e.g., Cactus, Bryophyllum, Kalanchoe, Sedum etc.) and other plants that normally grow in dry conditions. Such plants have a photosynthetic pathway similar to C₄ plants.

ii. CO₂ taken up by the leaves on green stems through open stomata during night and fixed as malic acid with the help of phosphoenol pyruvate.

iii. Calvin cycle takes place during the day when stomata are closed. Fomation of malic acid during dark is called acidification (Phase I) and the release of CO₂ for actual photosynthesis during day is called deacidification (Phase II).

iv. CAM is a type of adaptation that allows certain plants (e.g., pineapple) to carry out photosynthesis without much loss of water which is inevitable in plants with C₃ and C₄ mechanisms.

Factors Affecting Photosynthesis :

Blackman (1905) Proposed Law of limiting factors which states that “When a biological process is conditioned as to its rapidity by a number of separate factors, the rate of the process is limited by the pace of the slowest factor”.

1. Light

Provides energy for photosynthesis.

(i) Light quality:

Photosynthesis successfully takes place only in the visible light (3800 A – 7600 A wave length). Rate of photosynthesis is maximum in red light, average in blue light and minimum in green light.

(ii) Light intensity:

It has a direct relationship with the rate of photosynthesis. As the intensity of light (µ mol. M^-2S^-1) increases, the rate of photosynthesis increases. At higher light intensities, the rate of photosynthesis decreases.

(iii) Light duration:

Long continuous periods of light increase the rate of photosynthesis.

2. Carbon dioxide :

As the CO₂ concentration increases upto 0.9%, the rate of photosynthesis also increases. At the same time very high concentration of C0₂ becomes toxic to plants and inhibit photosynthesis.

3. Temperature :

Generally, the rate of photosynthesis increases by increase in temperature upto 40°C. High temperature results into the deactivation of enzymes and so, the dark reaction is affected. The effect of temperature varies from plant to plant. C₄ plants have higher optimum temperature than C^ plants. 25-30°C is the optimum temperature for photosynthesis.

4. Water :

It rarely acts as a limiting factor because less than 1 % of the water absorbed by a plant is used in photosynthesis. Electrons in the photochemical phase are supplied by the water but its availability for photosynthesis depends upon the closure of stomata. However, lowering of photosynthesis has been observed if the plants are inadequately supplied with water.

5. Nutrient supply :

Nitrogen has a direct relationship with photosynthesis since it is a basic part of chlorophyll and all enzymes involved in carbon reactions, so any reduction in nitrogen supply leads an adverse effect on photosynthesis. Deficiency of mineral elements (e.g., Mg, Fe, CI, Cu, Mn, P etc.) ultimately reduces photosynthesis.

6. Chlorophyll :

Emerson (1929) found the direct relationship between the chlorophyll content and the rate of photosynthesis.

Willstatter studied assimilatory number i.e., Photosynthesis/chlorophyll unit in leaves of different ages of plants and the effect of amount of chlorophyll on the rate of photosynthesis. Assimilatory number decreases with the age of the leaf.

7. Leaf Factors :

i.e., leaf age, leaf angle and leaf orientation etc. have effect on photosynthesis. Leaf age has the most prominent effect on photosynthesis. Rate of photosynthesis is maximum in just matured leaves but declines with age. In a senescence leaf there is deactivation of enzymes and degeneration of chlorophyll.