(1) The aggravation of the greenhouse effect is mainly due to the excessive burning of coal, oil and natural gas in modern industrial society. After burning these fuels, a large amount of carbon dioxide gas is released into the atmosphere. Carbon dioxide is also called greenhouse gas. The main way of carbon dioxide consumption is absorbed by plants for photosynthesis. Green plants absorb carbon dioxide in the air through photosynthesis, produce organic matter, store energy and release oxygen, which is conducive to maintaining the balance of carbon and oxygen in the atmosphere. It is automatic.

(2) The process [C] in the figure is that the remains of animals and plants are decomposed by bacteria and fungi, forming inorganic substances such as carbon dioxide, water and inorganic salts, and then returning to the environment to be used by plants. It can be seen that bacteria and fungi, as decomposers, promote the material circulation in nature; Animals A and B eat plants directly or indirectly, and promote material circulation as consumers.

(3) The food chain is the relationship between consumers and producers. Not including abiotic parts and decomposers, but the starting point is the producer. So a food chain in this agricultural ecosystem is crops → pigs → people.

This kind of agricultural ecosystem is characterized by realizing the recycling of materials and multi-level utilization of energy in the agricultural ecosystem, so it has the advantages of energy saving, environmental protection, efficient use of energy, reducing environmental pollution and improving economic benefits. Therefore, the model has high popularization value.

(4) To reduce the carbon dioxide in the atmosphere, one is to reduce its emissions, and the other is to absorb part of carbon dioxide through photosynthesis. Therefore, there are many ways to meet the "low-carbon life" in daily life, such as double-sided paper, walking instead of cars, or turning off the lights.

So the answer is: (1) carbon dioxide; Photosynthesis (making organic matter);

(2) bacteria, fungi, etc. (or microorganisms; Or decomposer); Consumers;

(3) crops → pigs → people;

Realizing the recycling of materials and multi-level utilization of energy in agricultural ecosystem has the advantages of energy saving, environmental protection, efficient utilization of energy, reducing environmental pollution and improving economic benefits;

(4) two-sided paper (or walk instead of car, etc.). ).