The "Paris Agreement" and its intended nationally determined contributions call for stabilizing global warming below 2°C(UNFCCC., 2015). To achieve this goal, we need to limit net greenhouse gas (GHG) emissions to 36 Pg CO2 equivalent per year(Meinshausen et al., 2009). Global change, particularly climate change caused by air temperature, rainfall, and strong heterogeneity of solar radiation distribution in time and space, is linked to the land ecological system structure, function, structure, and process of all-around and multi-level effects, such as temperature rise, extreme rainfall, and increased nitrogen concentration in the atmosphere, will change the advantage of wetland plant community composition. Accelerate soil organic carbon decomposition and inhibit plant growth, transforming the wetland from a carbon sink to a carbon release source. It is a great challenge for researchers to find a scientific and effective way to regulate the carbon and water cycle in the Earth's ecosystem. The fifth assessment of the Intergovernmental Panel on Climate Change (IPCC) identified agriculture as the most considerable GHG mitigation potential in the economic sector in the near term (up to 2030), which could be achieved primarily through Soil Organic Carbon (SOC) sequestration(Smith et al., 2014).
Wetlands are one of the world's three major ecosystems. As a sink of atmospheric CO2 and a source of CH4 release, it has the highest organic carbon storage per unit area of any terrestrial ecosystem, making it a potential indicator for the global carbon cycle. Peatlands have the highest carbon storage capacity per unit area of all terrestrial ecosystems(Yu et al., 2011). As a particular type of wetland, it accounts for one-third of the global terrestrial ecosystem soil carbon pool, or about 250–600 Pg, despite covering only 3% of the global land area. The estimated carbon storage of northern and subarctic peatland was about 455 Pg(Girham et al., 1991). The study estimates that 60 billion tons of carbon are sequestering from the atmosphere globally each year by the net primary productivity of photosynthetic plants(Cox et al., 2000). Peatland estimates global carbon accumulation range from 0.09 million tons to 50 million tons annually(Yu, Z.C., et al., 2011); carbon accounts for 1–5% of the world's annual anthropogenic greenhouse gas emissions(Friedlingstein et al., 2014). Research shows that the carbon pool sequestered in peat was less affected by global warming, with deep peat remaining stable even if the temperature rises by 9°C(Hodgkins, S.B., et al., 2018). Changes in the size of carbon sinks in peatlands may significantly affect global atmospheric CO2 concentrations(Charman et al., 2013). It is estimated that if all the carbon stored in peatlands were released into the atmosphere, it would increase the global average temperature between 0.8°C and 2.5°C. Peatlands worldwide are under great threat from human activities such as peat mining and occupation, among which agricultural reclamation and drainage are the main reasons for the large-scale reduction of peatlands and the transformation from "carbon sink" to "carbon source"(Bjørn, K., et al., 2000). Over the past 200 years, global peatland carbon stocks have fallen by about 4.1 billion tons, 60% of which was due to anthropogenic development. Currently, the drainage of peatlands causes 2 billion tons of carbon dioxide emissions each year, accounting for 6 percent of the world's anthropogenic carbon dioxide emissions. Therefore, protecting existing peatlands and expanding peatland areas is important for the current carbon-neutral background.
Soil Organic Carbon (SOC) is critical to global food production and mitigation of greenhouse gas emissions. "The '14th Five-Year Plan' for Energy Conservation and Emission Reduction" in China-proposed that agriculture had a huge carbon sink capacity through the absorption of carbon dioxide by crop photosynthesis and the enrichment and preservation of organic carbon by soil. The prospect of reducing agricultural emissions and increasing foreign exchange is comprehensive. Studies have shown that SOC uptake was mainly driven by plant carbon input. In addition, farming types that increase carbon input through crop selection and yield improvement measures can effectively improve farmland carbon sequestration capacity (Fan et al., 2019). China's peatland distribution is concentrated in the northeast Xinganling, Changbai mountain, Sanjiang plain, Ruoergai Plateau, Yunnan-Guizhou Plateau and other places.
The amount of carbon sequestration in agriculture is enormous, but to convert the amount of carbon sequestration into economic benefits, the corresponding carbon sequestration economic system must be established and improved. A carbon sink economy to increase carbon sink and promote carbon sink circulation and trade using carbon offset, carbon neutrality, or carbon investment. Realizing economic value through carbon sink is the fundamental goal of the carbon sink economy. The extension of the concept of carbon sink economy refers to various economic activities derived from enhancing carbon sink production and trading services. Related industries include ecological services associated with carbon sink production, development, management, and trading of voluntary emission reduction projects, and carbon finance.
In conclusion, the carbon sink economy and its related industries are not only ecological but also a new economic growth point. They can increase the enthusiasm of the people to develop carbon sink projects, and they are an essential part of ecological construction and the high-quality development of economic industries. For example, in most traditional farming agriculture areas in our country, because carbon investment exceeds the carbon sink ability of crops, farmland soil carbon is discharged to the atmosphere, becoming a huge carbon source. Similarly, finding carbon sink crops adapted to local conditions takes into account the dual advantages of environmental friendliness and the ability to generate income from carbon. Promote the realization of the "double carbon" policy; it has important practical and ecological significance.
Sphagnum has always played a role in plant carbon sinks due to its outstanding carbon sequestration and ability. In addition, Sphagnum is an excellent planting substrate with excellent water retention and soil fixation ability, which is widely used in the cultivation and transportation of rare flowers, so it also has certain economic value. Sphagnum is easy to grow and requires little soil nutrients, especially acidic and nutrient-poor soil with sufficient water. Local farmers call Sphagnum "Seaweed," so the government combined this title to establish a "10,000-mu Seaweed" planting base. This study explores the carbon sequestration ability and economic benefits of introducing Sphagnum into paddy fields. Moreover, the present study was conducted at the Longli County of Yunnan-Guizhou Plateau base to explore the feasibility of planting Sphagnum in farmland to increase agricultural carbon sinks and transform paddy soil into peat soil under the climate background suitable for peatland development. There are a large number of coal mines buried under the soil layer in this area. The high sulfur content in coal mines and the long-term humid environment in mountainous areas lead to soil acidification. The specific process is as follows:
2FeS2 + 7O2 + 2H2O → 2Fe3+ + 2H+ + 4SO42−
The resulting sulfuric acid weathers the surrounding rock and leaches potentially toxic metals and radioactive elements into the water. There are risks to planting rice in this area, but planting Sphagnum, a commercial crop can mitigate these risks. In addition, the area's hydrothermal and soil conditions are suitable for Sphagnum growth, which is an ideal experimental area for field planting of Sphagnum. This paper will analyze the ecological and economic value of planting Sphagnum in farmland to improve farmers' income and promote rural revitalization. The objectives of this paper are as follows: (1) to quantify the carbon emission parameters of the Sphagnum cropping system in Guizhou Province; (2) To evaluate the carbon sequestration capacity of the Sphagnum production system in farmland. This analysis provides a foundation for low-carbon agricultural planning policy formulation and proposes a method to optimize the carbon sink structure of farmland systems in southwest China's mountainous areas.