Grassland species structure optimization carbon promoting and sink increasing method

Abstract

The invention provides a grassland species structure optimization carbon promoting and sink increasing method, relates to the field of grassland carbon sink, and is characterized in that an annual leguminous plant vicia villosa and a gramineous plant lolium multiflorum are selected for mixed sowing based on ecological characteristics of grassland. The mixed sowing of the two green manure not only can increase the diversity and stability of grassland ecology, but also can quickly grow and die within one year, thereby increasing the input of dead root biomass. In addition, the leguminous plant Vicia villosa can fix nitrogen in the atmosphere, so that the grassland soil structure can be rapidly improved, and grassland plant growth can be promoted; the gramineous plant lolium multiflorum can effectively relieve the effective loss of soil phosphorus caused by the growth of the sweet potato, and the gramineous plant lolium multiflorum and the sweet potato can achieve the effects of mutual promotion and synergistic growth. The method is simple to operate, rapid and efficient, and has better popularization value.

Description

Technical Field

[0001] The present invention relates to the field of grassland carbon sink, and in particular to a method for promoting carbon sink by optimizing grassland species structure. Background Art

[0002] In recent decades, the global average annual temperature and carbon dioxide concentration have continued to rise, and global climate change has become a focus of concern for governments, the public and the scientific community. Studies have shown that soil carbon enhancement technology is an effective means to address global climate change and mitigate the greenhouse effect.

[0003] Grassland ecosystems are widely distributed on the earth. At the same time, grassland ecosystems are a huge carbon pool, accounting for one-third of the global terrestrial ecosystem carbon pool, second only to forest ecosystems. Compared with forest ecosystems, grasslands have higher vegetation coverage and shorter vegetation growth cycles, and have huge carbon sink potential. According to the assessment report released by the Intergovernmental Panel on Climate Change, 1ha of natural grassland can fix 1.3t of carbon per year, which is equivalent to reducing CO 2 Emissions were 6.9t. Improving the carbon sequestration capacity of grassland ecosystems is an important nature-based solution to achieve carbon neutrality. Grassland ecosystems have the dual functions of mitigating and adapting to climate change, which can enhance the carbon sequestration capacity of ecosystems and enhance their ability to adapt to climate change. Grassland biomass varies greatly from year to year and is sensitive to climate change and human activities. Accurately estimating the carbon sequestration capacity of grassland ecosystems is the scientific basis for the research and development of grassland sequestration technology and the sustainable use and management of grassland resources.

[0004] The organic carbon content in the soil is the result of a balance between the amount of plant residues entering the soil and the loss due to decomposition by soil microorganisms. Under natural conditions, the amount of plant residues entering the soil is determined by the vegetation type, so the vegetation type plays an important role in the accumulation of soil organic carbon. Differences in vegetation types lead to different amounts of litter and root biomass, which form different microclimates on the soil surface and inside, and affect the input and output of soil organic carbon by acting on soil microorganisms, resulting in significant differences in soil carbon storage and density between different vegetation types. The concentration of soil nutrients in different vegetation types is different, and the difference in soil nutrient content plays a key role in GPP and NEP. In nutrient-rich vegetation types, the higher the leaf nitrogen concentration (LNC), the stronger the photosynthesis it causes, and the significantly reduced C loss. Differences in vegetation coverage, litter, and plant root volume caused by vegetation types are also important factors affecting soil carbon sinks. Higher vegetation coverage, surface residual biomass, and underground biomass will promote the accumulation of organic carbon in the surface soil (0-15 cm). Therefore, it is of great significance to develop a carbon sequestration plan suitable for grasslands by combining multiple factors such as grassland soil conditions, climate, topography, and economic costs. Summary of the invention

[0005] The purpose of the present invention is to provide a method for promoting carbon sink by optimizing grassland species structure, which is simple and quick to operate, can quickly and efficiently improve the soil carbon sink of grassland according to the ecological environment of grassland, and has good promotion value.

[0006] The embodiment of the present invention is achieved as follows:

[0007] A method for promoting carbon sink by optimizing grassland species structure, characterized by comprising:

[0008] Plant glossy vetch and multiflora ryegrass in the grassland.

[0009] The beneficial effects of the embodiments of the present invention are:

[0010] The present invention provides a method for promoting carbon sink by optimizing grassland species structure. Based on the ecological characteristics of the grassland itself, the annual legume plant Vicia glabra and the gramineous plant Lolium multiflorum are selected for mixed sowing. The mixed sowing of these two green manures can not only increase the diversity and stability of grassland ecology, but also grow rapidly and die within one year, thereby increasing the input of dead root biomass. In addition, the legume plant Vicia glabra can fix nitrogen in the atmosphere, achieve rapid improvement of grassland soil structure and promote grassland plant growth; and the gramineous plant Lolium multiflorum can effectively alleviate the lack of effectiveness of soil phosphorus caused by the growth of Vicia glabra, and the two can promote each other and grow synergistically. The method is simple to operate, fast and efficient, and has good promotion value. DETAILED DESCRIPTION

[0011] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0012] The following is a detailed description of a method for promoting carbon sequestration by optimizing grassland species structure according to an embodiment of the present invention.

[0013] The embodiment of the present invention provides a method for promoting carbon sink by optimizing grassland species structure, which comprises:

[0014] Plant glossy vetch and multiflora ryegrass in the grassland.

[0015] There have been many studies on increasing the organic carbon content in the soil by planting green manure in the existing technology. However, traditional green manure planting usually adopts the practice of in-situ harvesting and plowing to return the field. There are problems such as low carbon sequestration efficiency, high economic and labor costs, and being unfavorable to improving soil fertility in terms of grassland soil carbon sequestration and sink. At the same time, the practice of in-situ harvesting and plowing to return the field will destroy the soil structure, which is not conducive to the formation of soil aggregates, and will hinder grassland soil carbon sequestration and emission reduction.

[0016] Nitrogen is an important component of chlorophyll, and chlorophyll is a key molecule in photosynthesis. With enough nitrogen, plants can synthesize more chlorophyll, thereby improving the efficiency of photosynthesis and increasing carbon fixation. Therefore, plant nitrogen fixation can improve the availability of nitrogen, promote photosynthesis and carbon assimilation accumulation, and play an important role in plant growth and ecosystem carbon cycle. The present invention adopts the annual leguminous plant glossy purple flower vetch, which has high yield, fast growth, strong adaptability, cold and drought resistance, dense stems and leaves, tender and juicy, and its protein content can reach more than 20%. It is rich in vitamins, amino acids and minerals, and is a high-quality feed for cattle, sheep, pigs and other livestock. As a high-quality biological fertilizer source, glossy purple flower vetch plays an important role in crop nutrient supply, farmland weed control, soil fertilization, regulation of bacterial community structure, water conservation and atmosphere regulation. At the same time, Vetch has good nitrogen fixation ability and can establish a symbiotic relationship with nitrogen-fixing bacteria, fixing nitrogen in the atmosphere into ammonia that can be used by plants, and converting it into amino acids, proteins and other nitrogen-containing organic matter, providing nitrogen nutrients required for plant growth. Secondly, it can also allow plants to synthesize more chlorophyll and improve the efficiency of photosynthesis, thereby fixing carbon to a greater extent and improving the carbon fixation efficiency of grasslands.

[0017] Lolium multiflorum belongs to the annual grass family. It has high yield, good grass quality, high nutritional value, and good palatability. It is an excellent forage grass among the grass family forage grasses. It can be used as green fodder, hay or silage, and is more suitable for grazing. Lolium multiflorum is also a good green manure crop. When planted in farmland, it can be used as green manure in the area before spring plowing and autumn planting. At the same time, it is also a pioneer grass species for reclaiming wasteland and an excellent variety for soil and water conservation. The inventors found that in the case of a single planting of glossy purple flower vetch, the growth of glossy purple flower vetch has a high demand for phosphorus, and the growth activity of nitrogen-fixing bacteria will further increase the demand for phosphorus, which will lead to a serious lack of soil phosphorus effectiveness, thereby limiting the growth of glossy purple flower vetch and affecting the storage of soil organic carbon and soil nutrients. This phenomenon can be effectively alleviated by mixed seeding of multiflora ryegrass. On the one hand, multiflora ryegrass itself has a relatively low demand for phosphorus, which helps to reduce the consumption of soil phosphorus. On the other hand, during its growth, multiflora ryegrass can secrete substances such as organic acids, which help to activate the phosphorus in the soil, thereby converting ineffective phosphorus into effective phosphorus and alleviating the problem of lack of soil phosphorus effectiveness.

[0018] Optionally, the sowing rate ratio of glossy purple vetch to multifloral ryegrass is 1:0.25-0.75. Under this ratio, the synergistic effect of glossy purple vetch and multifloral ryegrass is better, which can not only ensure a better carbon fixation effect, but also better alleviate the problem of lack of effectiveness of soil phosphorus.

[0019] Furthermore, the planting density of glossy purple vetch is 20-30 g / m 2 The planting density of multiflora ryegrass is 8-13g / m 2 Within this seeding rate range, the planting density of Vetch and Lolium multiflorum is more suitable, and the carbon fixation efficiency is higher.

[0020] The sowing time of glossy purple vetch and multiflora ryegrass is from March to April or from September to October every year. Sowing in this period can avoid the hot summer and cold season, which is conducive to the rapid growth of glossy purple vetch and multiflora ryegrass.

[0021] When sowing, choose an area with fertile soil, good drainage and plenty of sunshine for sowing; before sowing, maintain the pH of the sowing area at 6.0-8.0. It can be regulated by applying chemicals such as lime. On the one hand, regulation can provide suitable soil physical and chemical factors such as pH for the growth of green manure, and is beneficial to improve soil structure, promote the formation of soil aggregates, and protect soil organic carbon; on the other hand, this pH range is conducive to microbial activity, which can promote rapid nitrogen fixation by nitrogen-fixing bacteria, achieving the effect of nitrogen fixation and carbon promotion.

[0022] The sowing depth of glossy purple vetch and multiflora ryegrass is 1 to 2 cm. After sowing, the sowing area can be lightly compacted by foot or light roller to ensure that the seeds are in full contact with the soil.

[0023] In addition, before sowing, the seeds of Vicia glabra and Lolium multiflorum are pretreated by soaking in warm water, which can break the dormancy period of the seeds and promote germination. When soaking, the water temperature is 30-50℃ and the soaking time is 3-4 hours. Under this condition, the germination rate of the seeds is relatively high.

[0024] The present invention further comprises uniformly mixing the pretreated seeds with a liquid inoculum of nitrogen-fixing bacteria. Optionally, the nitrogen-fixing bacteria is rhizobium; after mixing, ensure that the surface of each seed is covered with the liquid inoculum of rhizobium, and after inoculation, take out the seeds and dry them in the shade until the seeds are no longer adhered to each other.

[0025] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0026] Example 1

[0027] This embodiment provides a method for promoting carbon sink by optimizing grassland species structure, which includes:

[0028] S1. Plant selection:

[0029] We purchase certified glossy vetch and multiflora ryegrass seeds, ensuring that the germination rate of the seeds is above 90%.

[0030] S2. Soil preparation:

[0031] Remove weeds, stones and other debris from the lawn area and ensure that the land surface is flat. According to the test results of the soil, make corresponding improvements, such as fertilizing, adjusting the pH, etc. Choose an area with fertile soil, good drainage and sufficient sunlight for replanting, avoid places that are too dark or waterlogged, and remove weeds and fallen leaves on the surface appropriately to ensure that the seeds can directly contact the soil.

[0032] S3. Seed weighing and pretreatment:

[0033] According to the size of the grassland, weigh 20g / m of glossy purple vetch seeds. 2 , Multiflora ryegrass seeds 8g / m 2 . Soak the seeds in 40℃ warm water for 3 hours before sowing to break the seed dormancy and promote germination.

[0034] S4. Inoculation of nitrogen-fixing bacteria:

[0035] Take out the pre-treated seeds, mix them with the purchased rhizobium liquid inoculant, and gently stir the seeds to ensure that the surface of each seed is covered with the rhizobium inoculant.

[0036] S5. Seed sowing:

[0037] The inoculated seeds should be sown within 24 hours. Spot sowing should be carried out in late March, with a sowing depth of about 1 cm. After sowing, the sowing area should be lightly compacted by foot to ensure that the seeds are in full contact with the soil. Using a light roller or plate to gently compact the grass seeds so that they are in close contact with the soil will help promote germination. Depending on the size and requirements of the grass seeds, a thin layer of soil should be covered to protect the grass seeds and promote their germination and growth.

[0038] S6. Management and maintenance:

[0039] Keep the soil moist after sowing, but avoid overwatering that causes waterlogging. The frequency and amount of watering should be adjusted according to soil moisture and weather conditions. Regularly remove weeds from the lawn to keep it clean and healthy. Pay attention to the growth of grass seeds and detect and prevent diseases and insect pests in a timely manner.

[0040] S7. Monitoring and Evaluation:

[0041] Regularly evaluate the growth of the plants, record the coverage, growth height, carbon content and health status. If the survival rate is low, appropriate replanting is required.

[0042] In this embodiment, the germination time of Vetch glabra seeds is 20 days, and the germination rate is 82%; the germination time of Lolium multiflorum seeds is 14 days, and the germination rate is 93%.

[0043] Example 2

[0044] This embodiment provides a method for promoting carbon sink by optimizing grassland species structure, which includes:

[0045] S1. Plant selection:

[0046] We purchase certified glossy vetch and multiflora ryegrass seeds, ensuring that the germination rate of the seeds is above 90%.

[0047] S2. Soil preparation:

[0048] Remove weeds, stones and other debris from the lawn area and ensure that the land surface is flat. According to the test results of the soil, make corresponding improvements, such as fertilizing, adjusting the pH, etc. Choose an area with fertile soil, good drainage and sufficient sunlight for replanting, avoid places that are too dark or waterlogged, and remove weeds and fallen leaves on the surface appropriately to ensure that the seeds can directly contact the soil.

[0049] S3. Seed weighing and pretreatment:

[0050] According to the size of the grassland, weigh 30g / m of glossy purple vetch seeds. 2 , Multiflora ryegrass seeds 13g / m 2 . Soak the seeds in 50℃ warm water for 4 hours before sowing to break the seed dormancy and promote germination.

[0051] S4. Inoculation of nitrogen-fixing bacteria:

[0052] Take out the pre-treated seeds, mix them with the purchased rhizobium liquid inoculant, and gently stir the seeds to ensure that the surface of each seed is covered with the rhizobium inoculant.

[0053] S5. Seed sowing:

[0054] The inoculated seeds should be sown within 24 hours. Drill sowing should be carried out in early October, with a sowing depth of about 1 cm. After sowing, the sowing area should be lightly compacted by foot to ensure that the seeds are in full contact with the soil. Using a light roller or plate to gently compact the grass seeds so that they are in close contact with the soil will help promote germination. Depending on the size and requirements of the grass seeds, a thin layer of soil should be applied to protect the grass seeds and promote their germination and growth.

[0055] S6. Management and maintenance:

[0056] Keep the soil moist after sowing, but avoid overwatering that causes waterlogging. The frequency and amount of watering should be adjusted according to soil moisture and weather conditions. Regularly remove weeds from the lawn to keep it clean and healthy. Pay attention to the growth of grass seeds and detect and prevent diseases and insect pests in a timely manner.

[0057] S7. Monitoring and Evaluation:

[0058] Regularly evaluate the growth of the plants, record the coverage, growth height, carbon content and health status. If the survival rate is low, appropriate replanting is required.

[0059] In this embodiment, the germination time of Vetch glabra seeds is 21 days, and the germination rate is 85%; the germination time of Lolium multiflorum seeds is 16 days, and the germination rate is 89%.

[0060] Example 3

[0061] This embodiment provides a method for promoting carbon sink by optimizing grassland species structure, which includes:

[0062] S1. Plant selection:

[0063] We purchase certified glossy vetch and multiflora ryegrass seeds, ensuring that the germination rate of the seeds is above 90%.

[0064] S2. Soil preparation:

[0065] Remove weeds, stones and other debris from the lawn area and ensure that the land surface is flat. According to the test results of the soil, make corresponding improvements, such as fertilizing, adjusting the pH, etc. Choose an area with fertile soil, good drainage and sufficient sunlight for replanting, avoid places that are too dark or waterlogged, and remove weeds and fallen leaves on the surface appropriately to ensure that the seeds can directly contact the soil.

[0066] S3. Seed weighing and pretreatment:

[0067] According to the size of the grassland, weigh 15g / m of glossy purple vetch seeds. 2 , Multiflora ryegrass seeds 10g / m 2 . Soak the seeds in 40℃ warm water for 4 hours before sowing to break the seed dormancy and promote germination.

[0068] S4. Inoculation of nitrogen-fixing bacteria:

[0069] Take out the pre-treated seeds, mix them with the purchased rhizobium liquid inoculant, and gently stir the seeds to ensure that the surface of each seed is covered with the rhizobium inoculant.

[0070] S5. Seed sowing:

[0071] After inoculation, the seeds should be sown within 24 hours. Drill sowing should be carried out in early March to ensure that the seeds are evenly spread over the sowing area and the sowing depth is about 1 cm. After sowing, gently compact the sowing area by foot to ensure that the seeds are in full contact with the soil. Use a light roller or plate to gently compact the grass seeds so that they are in close contact with the soil, which will help promote germination. Depending on the size and requirements of the grass seeds, cover with a thin layer of soil to protect the grass seeds and promote their germination and growth.

[0072] S6. Management and maintenance:

[0073] Keep the soil moist after sowing, but avoid overwatering that causes waterlogging. The frequency and amount of watering should be adjusted according to soil moisture and weather conditions. Regularly remove weeds from the lawn to keep it clean and healthy. Pay attention to the growth of grass seeds and detect and prevent diseases and insect pests in a timely manner.

[0074] S7. Monitoring and Evaluation:

[0075] Regularly evaluate the growth of the plants, record the coverage, growth height, carbon content and health status. If the survival rate is low, appropriate replanting is required.

[0076] In this embodiment, the germination time of Vetch glabra seeds is 18 days, and the germination rate is 81%; the germination time of Lolium multiflorum seeds is 15 days, and the germination rate is 91%.

[0077] Comparative Example 1

[0078] This comparative example provides a method for optimizing grassland species structure to promote carbon sequestration. The specific method is basically the same as that in Example 1, except that Vetch glabra is not planted and only Lolium multiflorum is planted.

[0079] In this comparative example, the germination time of Lolium multiflorum was 15 days, and the seed germination rate was 85%.

[0080] Comparative Example 2

[0081] This comparative example provides a method for optimizing grassland species structure to promote carbon sequestration. The specific method is basically the same as that in Example 1, except that Lolium multiflorum is not planted, and only Vetch glabra is planted.

[0082] In this comparative example, the germination time of Vetch seeds was 26 days, and the germination rate was 79%.

[0083] Comparative Example 3

[0084] This comparative example provides a method for optimizing grassland species structure to promote carbon sequestration. The specific method is basically the same as that in Example 1, except that Vetch. glabra is replaced by an equal amount of Medicago sativa L.

[0085] In this comparative example, the germination time of alfalfa seeds was 16 days, and the germination rate was 89%; the germination time of multiflora ryegrass seeds was 13 days, and the germination rate was 90%.

[0086] Comparative Example 4

[0087] This comparative example provides a method for optimizing grassland species structure to promote carbon sequestration. The specific method is basically the same as that in Example 1, except that the sowing rate of Vetch glabra is increased to 50 g / m 2 , the sowing rate of multiflora ryegrass was increased to 20g / m 2 .

[0088] In this comparative example, the germination time of Vetch seeds was 21 days, and the germination rate was 81%; the germination time of Lolium multiflorum seeds was 13 days, and the germination rate was 90%.

[0089] Comparative Example 5

[0090] This comparative example provides a method for optimizing grassland species structure to promote carbon sequestration. The specific method is basically the same as that in Example 1, except that the sowing rate of Vetch glabra is reduced to 8g / m 2 , the sowing rate of multiflora ryegrass was reduced to 3g / m 2 .

[0091] In this comparative example, the germination time of Vetch seeds was 20 days, and the germination rate was 83%; the germination time of Lolium multiflorum seeds was 14 days, and the germination rate was 91%.

[0092] Test example

[0093] The method for optimizing grassland species structure to promote carbon sequestration provided by Examples 1 to 3 and Comparative Examples 1 to 7 was adopted to carry out sowing in the respective experimental plots, and the experimental plots without planting green manure were used as blank cases. After one year of planting and cultivation, the surface soil of the experimental plots was sampled, and the samples were measured to evaluate the annual nitrogen and carbon fixation effects. The measurement results are shown in Table 1.

[0094] Table 1 Comparison of nitrogen fixation and carbon promotion effects of grassland water and fertilizer management

[0095]

[0096]

[0097] As can be seen from Table 1, after using the methods of Examples 1 to 3 of the present invention, the annual total carbon fixation of soil green manure reaches 3.0 to 3.3 tons / hectare, and under the influence of the nitrogen fixation effect of green manure, the annual carbon fixation of the grassland itself can be increased by 36% to 41%. This shows that nitrogen fixation has a significant carbon-promoting effect and can significantly enhance the carbon sink function of grassland soil.

[0098] In comparison, in Example 1, multiflora ryegrass was planted alone, and its annual total carbon fixation was only 1.1 tons / hectare; in Example 2, glossy-leaved purple flower vetch was planted alone, and its annual total carbon fixation was only 1.6 tons / hectare. In the case of mixed sowing in Example 1, the annual carbon fixation of each green manure was significantly higher than the annual carbon fixation of each green manure when planted alone. It can be seen that in the case of mixed sowing, the two green manures have a synergistic effect. In addition, in Example 1, multiflora ryegrass was planted alone, and the soil available phosphorus deficiency rate reached 11%, and in Example 2, glossy-leaved purple flower vetch was planted alone, and the soil available phosphorus deficiency rate reached 15%. In the case of mixed sowing of the two (Example 1), the soil available phosphorus deficiency rate can be reduced to 7%.

[0099] In Comparative Example 3, the glossy purple vetch was replaced with an equal amount of lucerne, and the total annual carbon fixation of green manure reached 2.6 tons / hectare, of which the contribution of multiflora ryegrass was 1.3 tons / hectare and the contribution of lucerne was 1.3 tons / hectare, and the annual organic carbon increase of the grassland was only 30%. It can be seen that the carbon fixation effect of lucerne is significantly lower than that of the combination of glossy purple vetch and multiflora ryegrass (Example 1).

[0100] Comparative Examples 5 and 6 investigated the effect of planting density on carbon fixation. It can be seen that when the sowing amount is increased (Comparative Example 5), the annual total carbon fixation of green manure has decreased, indicating that excessive planting density has restricted the growth of green manure and grassland itself, and the annual increase in organic carbon in grassland has only reached 30%. When the sowing amount is reduced (Comparative Example 6), the annual total carbon fixation of green manure has also decreased significantly, indicating that the sowing amount has not reached saturation and the carbon fixation effect of green manure has not been fully exerted.

[0101] In summary, the present invention provides a method for optimizing grassland species structure to promote carbon sinks. Based on the ecological characteristics of the grassland itself, the annual legume Vetch and the Gramineae multiflora ryegrass are selected for mixed sowing. The mixed sowing of these two green manures can not only increase the diversity and stability of grassland ecology, but also grow rapidly and die within a year, thereby increasing the input of dead root biomass. In addition, the legume Vetch can fix nitrogen in the atmosphere, achieve rapid improvement of grassland soil structure and promote grassland plant growth; and the Gramineae multiflora ryegrass can effectively alleviate the lack of effectiveness of soil phosphorus caused by the growth of Vetch, and the two can promote each other and grow synergistically. The method is simple to operate, fast and efficient, and has good promotion value.

[0102] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for promoting carbon sink by optimizing grassland species structure, characterized in that: include: Plant glossy vetch and multiflora ryegrass in the grassland.

2. The method for promoting carbon sink by optimizing grassland species structure according to claim 1, characterized in that: The sowing rate ratio of the glossy-leaved purple vetch to the multiflora ryegrass is 1:0.25-0.

75.

3. The method for promoting carbon sink by optimizing grassland species structure according to claim 2, characterized in that: The planting density of the glossy purple vetch is 20-30 g / m 2 .

4. The method for promoting carbon sink by optimizing grassland species structure according to claim 2, characterized in that: The planting density of the multiflora ryegrass is 8 to 13 g / m 2 .

5. The method for promoting carbon sink by optimizing grassland species structure according to claim 3, characterized in that: The sowing time of the glossy-leaved purple vetch and the multiflora ryegrass is from March to April or from September to October every year.

6. The method for promoting carbon sink by optimizing grassland species structure according to claim 1, characterized in that: When sowing, choose an area with fertile soil, good drainage and sufficient sunlight; maintain the pH of the sowing area at 6.0-8.0 before sowing.

7. The method for promoting carbon sink by optimizing grassland species structure according to claim 1, characterized in that: The glossy-leaved purple vetch and the multiflora ryegrass are sown in the form of spot sowing or row sowing, and the sowing depth of the glossy-leaved purple vetch and the multiflora ryegrass is 1 to 2 cm.

8. The method for promoting carbon sink by optimizing grassland species structure according to claim 1, characterized in that: Before sowing, the seeds of the Vetch glabra and the Lolium multiflorum are pretreated by soaking them in warm water; during the soaking, the water temperature is 30-50° C. and the soaking time is 3-4 hours.

9. The method for promoting carbon sink by optimizing grassland species structure according to claim 8, characterized in that: The pretreated seeds are uniformly mixed with a liquid inoculum of nitrogen-fixing bacteria.

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