Plants in diverse ecosystems have developed various strategies to adapt to their environments, especially when it comes to photosynthesis.
The two common strategies are the C3 and C4 pathways, each named for the number of carbon atoms in the first compound produced during photosynthesis.
Let’s briefly describe what C3 and C4 plants are, and explore more about their preferred pathways to derive critical differences that distinguish the plants as we know them today.
What Are C3 Plants?
C3 plants are named after the three-carbon compound, 3-phosphoglycerate, which is the first stable product of photosynthesis in this pathway. They use the Calvin cycle in the dark reaction of photosynthesis. Put simply, these plants only conduct photosynthesis when the stomata are open.
The C3 pathway is the most common form of photosynthesis (representing about 95% of the green plants) in the flora world including trees, shrubs, and cool-season grasses.
This category of plants can be annual perennial and also classified as temperate plants. They are well adapted for cooler and shaded environments where they can efficiently carry out photosynthesis.
What Are C4 Plants?
C4 plants are named after the four-carbon compound (oxaloacetate) that is first formed during their unique photosynthetic process. This pathway, also called the Hatch-Slack pathway, evolved in some plants as an adaptation to high light intensities, high temperatures, and aridity.
Plants in this category first convert the carbon dioxide into a four-carbon compound before entering the C3 cycle. This pathway allows for more efficient photosynthesis compared to C3 plants.
C4 plants are typically found in tropical and subtropical regions where conditions are hot and dry. They include many summer grasses and crops such as maize, sugarcane, sorghum, and millet.
What Are the Differences Between C3 and C4 Plants?
Based on the descriptions above we can derive several differences between the C3 and C4 plants.
They are summarized in the table below:
| C3 Plants | C4 Plants |
| C3 photosynthesis is the oldest and the most common form. | C4 photosynthesis is a recent phenomenon evolving due to environmental changes. |
Produce three-carbon compound, (3-phosphoglycerate) as the first stable product of photosynthesis. | Produce four-carbon compound (oxaloacetate) as the first stable product of photosynthesis. |
| Common in temperate climates. | Common in tropical and subtropical climates. |
| Their optimal environments are cool and moist with moderate sunlight. | Their optimal environments are hot and dry with high temperatures. |
| Completes carbon fixation once. | Completes carbon fixation twice. |
| Covers 95% of the green plants. | Covers 5% of green plants. |
| The leaf anatomy is less specialized with photosynthetic functions occurring on the mesophyll cells. | The leaf anatomy is more specialized with photosynthetic functions occurring on the mesophyll and bundle sheath cells. |
Photosynthesis occurs when the stomata are open. | Photosynthesis occurs when the stomata are closed. |
| Examples include spinach, wheat, rice, peanuts, and soybeans. | Examples include many summer grasses, maize, sorghum, and sugarcane. |
The differences between C3 and C4 plants underscore the diversity of plant life’s strategies for survival and success. Each photosynthetic pathway offers distinct advantages and disadvantages, shaped by evolutionary challenges over the years. Overall, the resilient plants clearly show what survival for the fittest truly stands for.
Lead Editor for Insight Weeds.