1. energy flow
Plants and some autotrophic bacteria fix solar energy in the form of organic compounds through photosynthesis, and then consume it for many consumers, or convert it into other forms of energy through different types of food chains. The whole energy flow process is consumed step by step, and will not be circulated.
2. Material circulation
In an ecosystem, material circulation and energy flow always go hand in hand. The energy flow is one-way flow, and finally it is converted into heat energy and consumed. The material flow is endless. Producers convert inorganic substances into organic substances while absorbing solar energy. These organic substances directly or indirectly become organic fragments, which are decomposed into inorganic substances by decomposers and return to abiotic environment for recycling by producers. There are many kinds of material circulation. This paper mainly introduces carbon cycle, oxygen cycle and nitrogen cycle.
Carbon-oxygen cycle
49% of the dry weight of organic matter is composed of carbon. When green plants carry out photosynthesis, CO2 in the atmosphere is fixed as organic matter, and carbon cycle begins. Producers, consumers and decomposers emit carbon dioxide into the atmosphere through breathing. After the death of producers and consumers, protein, fat and carbohydrates are finally decomposed into CO2, water and inorganic salts by decomposers, and CO2 returns to the atmosphere. In the long geological period, the carbon cycle has been going on, part of carbon will be fixed in the form of limestone, and part of CO2 will be released into the atmosphere after the later karstification. Another part of carbon will be stored in the form of coal or oil, which will be used by human beings or naturally degraded to become CO2, and then returned to the atmosphere for recycling, thus increasing the CO2 content in the atmosphere.
When animals and plants breathe, they need O2 in the atmosphere and exhale CO2. When green plants carry out photosynthesis, they produce O2 and release it into the atmosphere and water. At present, most of O2 in the atmosphere is the result of long-term production and accumulation of plants in the process of biological evolution. Green plants can not only produce O2 under photosynthesis, but also fix carbon and maintain the balance of carbon and oxygen. Therefore, protecting and increasing green plants is the most effective way to reduce CO2 and increase O2 content in the atmosphere.
nitrogen cycle
N2 accounts for 78% of the atmosphere, and these free N2 can't be used by most organisms. Nitrogen must be absorbed by plant roots in the form of ammonium salt, nitrite and nitrate. The process of transforming N2 into ammonium salt, nitrite and nitrate is called nitrification, which is completed by nitrogen-fixing bacteria, cyanobacteria and rhizobia. Ammonium salts and nitrates entering plants combine with carbon through biochemical reactions to form amino acids, and then protein and nucleic acids are synthesized to form plant organisms together with other substances in plants. After animals and plants die, microorganisms decompose protein into amino acids, and then into ammonia, CO2 and water. This process is called ammoniation and denitrification. Ammonia entering the soil can be reused by plants. Under anaerobic conditions, denitrification is very strong.
In nature, the processes of nitrification and denitrification are balanced. Large-scale destruction of vegetation and large-scale industrial production of nitrogen-containing chemical products will cause the destruction of nitrogen balance in nature.
3. Ecosystem information transmission
There is also information transmission between organisms in the ecosystem. Information transmission links all components of the ecosystem into a whole and has the function of regulating the stability of the system. At present, the known information transmission methods mainly include nutritional information, physical information, chemical information and behavioral information.
Nutritional information: it is a form of transmitting information between one individual or group and another through nutritional exchange. The food chain is the representative of nutrition information transmission.
Physical information: information transmitted through physical processes, including sound, light, color, etc. For example, animals make different sounds to inform their companions of the environmental information they feel or send threatening signals to other animals; Flowers transmit pollination information to butterflies with bright colors; Fireflies recognize their companions by flashing lights.
Chemical information: Metabolic substances produced by organisms, such as enzymes, auxin, sex pheromone, unsaturated lactone of sesame oil, etc. , can pass information. For example, dogs use urine and other excreta to mark the route; Tigers use feces to mark their sphere of influence; In estrus, females will send out sex pheromones to attract males; Mammals, such as dogs and pandas, judge kinship only by the smell of their excrement sticking to their cubs.
Behavioral information: In the same population, individuals transmit information to each other through body movements. For example, ants and bees use different body movements to inform their companions of the location of food and other information; Red-crowned cranes show their kindness to the opposite sex with graceful dancing.
4. The service function of ecosystem
Ecosystem provides essential material resources and living environment for human beings, and is the cornerstone of human social, economic and cultural development. The substances produced by ecosystems and ecological processes and the good living environment they maintain are called ecosystem services, including the continuous provision of products and life support functions. The ecosystem service mentioned here mainly refers to the life support function, and the ecosystem can provide many kinds of services. Here are just a few services related to water resources and environment.
Water saving and drought resistance
One of the main functions of forest ecosystem is to reduce the direct erosion of rain on the surface, delay the occurrence of floods, increase the recharge of groundwater by precipitation, conserve water and slow down drought.
According to the measurement, the rainwater intercepted by the forest canopy can account for 15% ~ 40% of the rainfall, and 5% ~ 10% of the rainfall can be absorbed by the litter. Rainfall intercepted by canopy is related to the ecological characteristics of tree species. Shade-tolerant trees have dense branches and leaves and dense crowns, and retain more water than positive trees. For example, spruce canopy can intercept 30% of the total rainfall, pine forest is 18%, and birch forest is only 9%.
The roots, branches and leaves, soil and dead branches and leaves of forest communities keep rainwater in woodlands with high relative humidity, humid air and gurgling streams. The woodland soil is loose and has good water permeability, which can accumulate most of the precipitation. Such woodland is called water source forest. The implied water content per 1hm2 of forest land is at least 300m3 more than that of non-forest land. Due to the interception of precipitation by forest plant communities, surface runoff is greatly reduced, which not only avoids soil erosion, but also effectively prevents the fluctuation of rivers, reduces flood disasters and has a good regulating effect on water resources. For example, in August of 1975, in Zhumadian, Henan Province, a sudden rainstorm caused the dam failure of Banqiao Reservoir and Shimantan Reservoir, resulting in huge loss of life and property. Because the forest coverage rate in the upper reaches of Baoshan and Dongfeng reservoirs in the same area is above 90%, although the same precipitation exceeds the storage capacity, due to the effective interception of forests, the time of centralized flood storage is greatly delayed and the flood discharge is smooth, but the two reservoirs are safe and sound.
Protect and improve environmental quality
In the natural system, organisms make chemical elements enter the circulation process through the metabolic process and the accompanying biological oxidation and reduction, which effectively prevents the excessive accumulation of waste materials from causing pollution. Some toxic substances in the environment can be eliminated or reduced by biological absorption and degradation, thus improving environmental quality.
Plants absorb a lot of CO2 and release O2 through photosynthesis. The broad-leaved forest with1hm ~ 2 can absorb 1t CO2 and release 0.73t O2 a day, which can be used by 1000 people to breathe. The oxygen content in the air of lush forests and grasslands is higher than that in bare areas.
Plant branches and leaves have a good filtering and retention effect on smoke and dust. The surface of plant leaves is uneven, fluffy or secretes mucus, which can effectively retain dust. The average 1hm2 pine forest can retain 36.4t of dust every year, and the dust content in the air above the green space is much lower than that in the street without green space, usually 37% ~ 60% less.
Many tree species have the functions of absorbing harmful gases and sterilizing. For example, plants such as oleander, magnolia grandiflora and phoenix tree can absorb HF; Trees such as Sophora japonica, mulberry, weeping willow and Podocarpus can absorb SO2. Cypress, Pinus bungeana, Cedar, Cinnamomum camphora and Lagerstroemia can secrete fungicides, which can kill tuberculosis, dysentery, typhoid fever and diphtheria. In a word, the plant community has a good air purification function.
Adjust and improve the climate
There are dense trees in the forest, developed irrigation layer and herb layer under the forest, slow airflow and small temperature difference; The surface evaporation in forest is small, generally only 40% ~ 80% of that in non-forest land, and the relative humidity is higher than that in non-forest land 10% ~ 26%. Vegetation has a good function of regulating and improving climate.
Forest transpiration plays an important role in natural water cycle and improving regional climate. The research shows that 1 hm ~ 2 forest absorbs 70 ~ 100 t of groundwater every day, and most of it returns to the atmosphere through transpiration. Leaves absorb a lot of solar radiation for photosynthesis, and water also absorbs heat when it is converted into steam. Therefore, the big forest can not only adjust the temperature, but also make the air moist, with more fog, dew, frost and snow, which significantly improves the regional climate. For example, in Leizhou Peninsula, Guangdong Province, after 1950, the afforestation area is 27× 104hm2, and the coverage rate is 36%. According to the records of the local weather station, after 20 years of afforestation, the average annual precipitation increased to 1855mm, which was 3 1% higher than that in the 40 years before afforestation, the evaporation decreased by 75%, and the relative humidity increased by 1.5%, which changed the original severe drought climate.
Urban green space can effectively regulate urban temperature. Modern cities are densely populated and industries are concentrated. Solar radiation and man-made heat have heated concrete buildings and roads all over the city, but the heat lost by evaporation is very small, which leads to the heat island effect that the temperature in the city is higher than that in the suburbs. The green space, forest and water surface around and inside the city can effectively increase the latent heat flux and change the direction of heat transmission, thus achieving the effect of regulating the urban climate. The research shows that when the urban temperature is 27.5℃ in summer, the lawn temperature is only 22 ~ 24.5℃, which is 6 ~ 7℃ lower than that of bare land and 8 ~ 20.5℃ lower than that of asphalt road. In Shanghai, the temperature of the wall with wisteria greening is 5℃ lower than the average temperature of the bare wall.
wind prevention and sand fixation
Wind erosion is a common geological disaster in north and northwest China. As a geological force, wind can not only blow the surface soil and form various wind erosion landforms, but also form and carry sand dunes, cover up farmland and make the ecological environment worse and worse. Strong wind will roll up a lot of dust in the dust source and bring it into the sky to become a sandstorm with a wide influence area.
Grassland and woodland with high coverage can effectively reduce wind erosion and play a role in preventing wind and fixing sand. When the wind passes through the shelter forest or woodland, it is blocked by the branches and leaves of plants and divided into many small airflow in different directions. The wind forces cancel each other, and the wind speed is significantly reduced, which makes the strong wind weak and greatly reduces the erosion and bearing capacity of the wind. According to local observation, the forest belt with a height of 10m m will reduce the wind force by more than 50% on average within the range of 150m on its back. Within 250 meters, the average wind power drops by more than 30%.
In the desert area of our country, 240 clumps of Salix psammophila or Artemisia sphaerocephala are planted on each mu of mobile sand dunes. After 4 years, the sand dunes can be fixed, and the near-surface wind speed will be reduced from 8 to 5. But planting 50 Salix psammophila, 200 shrubs and 200 grasses per mu will fix the dunes in five years, and the wind speed will drop to 3 ~ 4.
What are the main functions of an ecosystem?
The function of ecosystem refers to the ability of ecosystem to realize normal operation through species, species and environment. A healthy ecosystem must be self-sustaining, self-regulating and self-repairing, which requires the ecosystem to do work. The basic functions of ecosystem include energy flow, material circulation and information transmission.
1 energy flow
Objects need energy to do work, and ecosystems also need energy, but this energy is made by the ecosystem itself. Energy flow refers to the process of energy input, transmission, transformation and disappearance in the ecosystem. Energy flow is an important function of ecosystem. In an ecosystem, the close relationship between organisms, environment and organisms is realized through energy flow.
The energy flow of the ecosystem begins with the solar energy fixed by the producers through photosynthesis, and is completed by various green plants on the land and various algae in the ocean. The total energy flowing into the ecosystem is the total solar energy fixed by the producers through photosynthesis, and the energy is transmitted through the food chain and food web. The energy flowing into a trophic level refers to the energy absorbed by the organisms in that trophic level. The energy assimilated by a trophic organism is generally used in four aspects: first, its own respiratory consumption; Second, it is used for growth, development and reproduction, and its energy is stored in organic matter that constitutes organisms; The third is the unused part of the organism that flows into the next trophic level. Fourth, it is used by decomposers, and part of the energy in organic matter is decomposed by decomposers, such as corpse wreckage, debris, excrement, etc. In the ecosystem, energy flow and carbon cycle are closely linked.
The energy flow of ecosystem has the characteristics of one-way flow and decreasing. One-way flow means that the energy flow of the ecosystem can only flow from the first trophic level to the second trophic level, and then to the subsequent trophic levels in turn, and generally cannot flow in the opposite direction. This is determined by the nutritional structure formed by the long-term evolution of organisms.
Three functions and characteristics of ecosystem
The three functions of ecosystem are energy flow, material circulation and information transmission.
1, the energy flow has two characteristics, namely, the energy flow is unidirectional and the energy decreases step by step.
2. Material circulation refers to the energy flow of the ecosystem to promote the circulation of various substances between the biological community and the inorganic environment. The substances here include the basic elements of organisms: carbon, nitrogen, sulfur, phosphorus, and toxic substances represented by DDT, which can exist stably for a long time.
3. Information transmission refers to physical information transmitted through physical processes, which can come from inorganic environment/biological community, mainly including: sound, light, temperature, humidity, magnetic force, mechanical vibration, etc.
Extended data:
I. Ecological value
1, potential value
Potential value refers to the value that human beings have not yet defined.
2. Direct value
Direct value includes values that have no practical significance to human medicine, bionics, literature and art, tourism and so on.
3. Indirect value
Indirect value, also known as "ecological function", refers to the function of stabilizing and regulating the ecological environment, such as the function of flood storage and drought prevention in wetland ecosystem, and the function of preventing soil erosion in forests and grasslands. The indirect value of biodiversity is far greater than the direct value.
Second, the composition of the ecosystem
Abiotic matter and energy, producers, consumers, decomposers. Producers are the main components. Different ecosystems are: forest ecosystem, grassland ecosystem, marine ecosystem, fresh water ecosystem, farmland ecosystem, frozen original ecosystem, wetland ecosystem and urban ecosystem.
Among them, the inorganic environment is the foundation of an ecosystem, and its conditions directly determine the complexity of the ecosystem and the richness of the biological communities in it.
The response of biological community to inorganic environment. Biological communities not only adapt to the environment in the ecosystem, but also change the appearance of the surrounding environment. Various alkaline substances closely link biological communities with inorganic environment.
The primary succession of biological communities can even turn a desolate and bare land into an oasis rich in aquatic plants. The close relationship between the components of the ecosystem makes the ecosystem an organic whole with certain functions.
Baidu encyclopedia-ecosystem