Factors affecting photosynthesis

In high school, people should have learned the term photosynthesis. Most plants need photosynthesis to grow. If they do not absorb enough sunlight, the growth of plants will be slow. Visible photosynthesis is indeed very important for plants. However, photosynthesis will be affected by many factors. Once affected, the photosynthetic effect will be greatly reduced. Here we will introduce some factors that affect photosynthesis.

(I) Light

1. Light intensity

Different plants have different light intensity photosynthetic curves, and the light compensation point and light saturation point also vary greatly. Plants with high light compensation points generally have high light saturation points. The light compensation points and light saturation points of herbaceous plants are usually higher than those of woody plants. The light compensation points and light saturation points of sun-loving plants are higher than those of shade-loving plants.

2. Light quality

Under natural conditions, plants are exposed to light of different wavelengths to greater or lesser extents. For example, on a cloudy day, not only does the light intensity decrease, but the proportion of blue and green light also increases. The leaves of trees absorb more red and blue light, so there is more green light in the light that passes through the tree canopy. Since green light is inefficient light for photosynthesis, it will make the plants growing under the tree canopy, which already have insufficient light, use light energy even less efficiently. This is the reason why "there is no lush grass under a big tree".

3. Light exposure time

Since the length of illumination time has a great influence on the photosynthetic rate of plant leaves, the leaves must be fully pre-illuminated when measuring the photosynthetic rate.

(ii) CO2

CO2 photosynthetic curve The CO2 photosynthetic curve is similar to the light intensity photosynthetic curve, with a proportional stage and a saturation stage. When the CO2 concentration is zero under light, the leaves only release CO2 through light and dark respiration.

This is particularly evident in C3 plants.

(III) Temperature

The dark reaction in the photosynthetic process is a chemical reaction catalyzed by enzymes and is therefore affected by temperature. The effect of temperature on photosynthesis rate is greater under strong light and high CO2 concentration than under weak light and low CO2 concentration. This is because under strong light and high CO2 conditions, temperature can become the main limiting factor of photosynthesis.

(IV) Water content

There are both direct and indirect reasons why water affects photosynthesis. The direct reason is that water is the raw material for photosynthesis, and photosynthesis cannot be carried out without water. However, the water used for photosynthesis is less than 1% of the water lost through transpiration, so water shortage affects photosynthesis mainly indirectly.

(V) Mineral nutrition

The functions of mineral nutrition in photosynthesis are extremely extensive, which can be summarized as follows:

1. The components of chloroplast structure such as N, P, S, and Mg are indispensable for the formation of chlorophyll, protein, nucleic acid, and lamellar membrane in chloroplasts.

2. Important components of electron transfer bodies such as PC contain Cu, Fe-S center, Cytb, Cytf and Fd all contain Fe, and Mn2+ and Cl- are indispensable for oxygen-releasing complexes.

3. The important role of the phosphate group: ATP and NADPH that constitute the assimilative power, all the intermediates in the photosynthetic carbon reduction cycle, ADPG, the precursor of starch synthesis, and UDPG, the precursor of sucrose synthesis, all these compounds contain phosphate groups.

4. Activation or regulatory factors such as Mg2+ are required for the activation of enzymes such as Rubisco and FBPase; Fe, Cu, Mn, and Zn are involved in the synthesis of chlorophyll; K+ and Ca2+ regulate the opening and closing of stomata; K and P promote the conversion and transport of photosynthetic products, etc.

(VI) Daily variation of photosynthetic rate

Photosynthetic "nap" is a common phenomenon that occurs when plants encounter drought, and it is also a way for plants to adapt to environmental water shortages. However, the losses caused by "nap" can reach 30% of photosynthetic production, or even more, so timely irrigation should be carried out in production, or drought-resistant varieties should be selected to enhance photosynthetic capacity in order to alleviate the degree of "nap".