Ecosystem is the basic functional unit for energy conversion and material cycle between organisms and the environment, and is a unified whole that interacts through energy flow and material cycle among various organisms and between biological communities and inorganic environments. The largest ecosystem on Earth is the biosphere, and the largest ecosystem on land is the forest ecosystem. The ecosystem mainly consists of four parts. Namely the abiotic environment, producers, consumers and decomposers. Forest ecosystem (1) Abiotic environment includes: climatic factors, such as light, temperature, humidity, wind, rain and snow, etc.; inorganic substances, such as carbon, hydrogen, oxygen, nitrogen, carbon dioxide, and various inorganic salts; organic substances , such as proteins, carbohydrates, lipids and humus. Lakes and wetlands (2) Producers mainly refer to green plants, which are autotrophic organisms that can use simple inorganic substances to produce food, and play a leading role in the ecosystem. (3) Consumers are heterotrophic organisms, which mainly refer to various animals that feed on other organisms, including herbivores, carnivores, omnivores, and parasites. (4) Decomposers also belong to heterotrophs, mainly bacteria and fungi, and also include some protozoa and large scavenging animals such as earthworms, termites, and vultures. They decompose animal and plant residues, feces and various complex organic compounds, absorb some decomposition products, and decompose organic matter into simple inorganic substances, which can be reused by autotrophic organisms after recycling. The ecosystem consists of four subsystems, namely forest ecosystem, grassland ecosystem, marine ecosystem, wetland ecosystem and farmland ecosystem. (1) Forest ecosystems are mainly distributed in humid areas. Its main feature is that there are many kinds of animals and plants, the structure of the community is complex, and the density of the population and the structure of the community can be in a relatively stable state for a long time. Forest ecosystems are known as 'green reservoirs'. (2) Grassland ecosystems are distributed in arid regions, where annual rainfall is very little. Compared with forest ecosystems, grassland ecosystems have much fewer species of animals and plants, and the community structure is not as complex as the former. The plants on the grasslands are mainly herbaceous plants, and some grasslands have a small amount of shrubs. Due to the lack of rainfall, trees are very rare. Therefore, the rational use and protection of grassland must be strengthened. (3) Marine ecosystem. The ocean covers 71% of the Earth's surface. The types of life in the ocean are very different from those on land. The vast majority of plants in the ocean are tiny phytoplankton. There are many types of animals in the ocean, from single-celled protozoa to the largest individual blue whale among animals, most of which can swim in the water. Marine Ecosystem (4) Wetland Ecosystem. People usually refer to swamps and coastal tidal flats as wetlands. There are many types of wetlands in my country, with rivers criss-crossing, lakes dotted all over, and swamps scattered north and south. Moreover, wetlands are often directly used by people as a source of domestic water, industrial and agricultural water. Wetlands have huge ecological and social benefits. Wetland ecosystem (5) Farmland ecosystem is an artificially established ecosystem. Its main feature is that the role of people is very critical, and people are the main members of this ecosystem. There are fewer animal species in the farmland, and the organization of the community is single. Once the role of humans disappears, the farmland ecosystem will quickly degrade, and the dominant crops will be replaced by weeds and other plants.