Carbon fixation stage in photosynthesis

In the photosynthesis and initial carbon fixation occur at night and a 4-carbon acid is stored in the cell's vacuole. During the day, the Calvin cycle operates in the same chloroplasts.

Mechanism of nitrogen fixation

The carbon fixation stage occurs in the stroma and results in the production of .

C3 photosynthesis: activation of RuBISCO and Carbon dioxide fixation.

Moroney JV and Somanchi A (1999) How do algae concentrate CO2 to increase the efficiency of photosynthetic carbon fixation? Plant Physiology 119: 9–16.

for CO2 fixation by aquatic plants in The differences in

However, they were unable at first to identify a 2-carbon molecule that could bond with CO2 to form 3-PG. They did deduce that this was a cyclic process, because at longer times, the other carbons of 3-PG became labeled. This figure shows a model of their initial findings:

This video explains how this process (carbon fixation) works in the Calvin cycle:
30-40o .the incorporation of CO2 into RuBP is the only way for carbon fixation thereby limits plant growth.

Carbon fixation (The Calvin Cycle)

Zinc in the soil

The zinc content of unpolluted soils ranges between 10 – 80 mg kg-1 and the Zn content of sandy soils is generally lower than that of loamy soils. Freely available zinc in the soil solution binds mainly to the organic matter in the soil. In addition, it can be found adsorbed onto iron, manganese and aluminium oxides or strongly bound to the lattice of clay minerals and silicates. Additional immobilisation of zinc occurs when the sulphate and phosphate content in the soil solution are excessive. The availability of zinc is strongly affected by the pH and the total Zinc content of the soil. The proportion of exchangeable Zinc decreases with increasing pH and is already greatly reduced at pH 6. With increasing pH, the affinity of zinc to manganese oxide and iron oxide increases strongly. Under anaerobic conditions, zinc can be precipitated into the barely soluble sulphide form which is largely unavailable to plants Zinc can be leached from the soil but this process generally only occurs in acidic soils.

Zinc in the plant


Zinc is taken up by plants from the soil solution either as the Zn2+ ion (at low pH) or as the zinc hydroxide ion (at higher pH values). Plants grown in acid conditions of less than pH 6 are rarely short of Zinc since the availability under such conditions increases greatly. Zinc activates or is a component of several enzymes and therefore affects many metabolic processes in the plant.

Functions of zinc in the plant:


Zinc deficiency symptoms


Zinc toxicity

An excess of Zinc can be toxic in plants although the tolerance levels are usually high. Some plants are able to store surplus zinc in their vacuoles. Zinc toxicity results in:

Each has The second pathway is the so-called

Carbon fixation | Biology 1510 Biological Principles

Phosphorus in the soil

The total phosphorus content of soils is generally high. However, only a fraction of it is available directly to the plant and the majority is adsorbed to the soil.

Phosphate dynamics in soils

The availability of phosphorus can be categorised as follows:



~ Orthophosphate in the form of H2PO4- and HPO42-.



~ P fraction which has been adsorbed onto oxides and hydroxides of iron or aluminium as well as clay mineral.

~ calcium-, magnesium-, potassium-, sodium- and ammonium phosphate depending on the concentration of cations in the soil solution.

~ easily soluble organically bound phosphorus.



~ calcium-, iron- and aluminium phosphate (inorganic)




Effect of pH on P availability:

The availability of phosphorus in the soil depends largely on the pH value. The greatest mobilisation occurs at a pH value between 6 and 7. The danger of phosphorus fixation is greater with an increasing soil pH. However, the availability can be improved at a relatively high pH (7.5-8) through addition of organic matter and at a high pH (>8) from addition of S or gypsum.

Increasing acidity of the soil results in the development of aluminium and iron phosphate. The availability of phosphorus can be improved by liming of the soil.


Effect of phosphorus fertilisation on the soil:



Soil fertility status


The fraction of phosphorus that is easily taken up from the soil solution is the important fraction for plant nutrition. Analysing soil for its plant available nutrients is a useful tool in calculating fertiliser requirements. Most countries have a scale of available P in soils and different crops require different P levels according to the responsiveness of that crop to P. It is important that P is neither limiting nor in excess since an excess of P not only increases the risk of leaching into the environment but also can cause problems with micronutrient availability.


Phosphorus in the plant


P is mainly taken up from the soil solution in the orthophosphorus form by the root hairs. These hairs are also able to solubilise a proportion of the unstable phosphate fraction through the excretion of acids. Therefore, a well developed root system is essential for the uptake of phosphorus.

Phosphorus is irreplaceable as a main nutrient for the plant. It is the constituent part of many plant compounds and affects the entire plant metabolism.


Functions of phosphorus in the plant:




Phosphorus deficiency symptoms

Carbon fixation and light - What is the link between the light dependent and the light independent pathways?

Photosynthesis: carbon fixation by the C3 and C4 pathways ..

Typical daily patterns of CO2 fixation and the reciprocal malic acid and glucan (carbohydrates) and CO2 stress, i.e., protection against a CO2 limit-.Environment Adaptation C3 vs.