A method for promoting the accumulation of organic carbon in karst soils

Abstract

The present invention discloses a method for promoting organic carbon accumulation in karst soils. The method involves first investigating soil pH and initial soil calcium content, then inoculating a mixed inoculant of three arbuscular mycorrhizal fungi, namely, Glomus mosseae, Glomus intraradici, and Glomus juvenile, near plant roots. Furthermore, varying weights of calcium carbonate powder are added based on soil pH and calcium content. Finally, soil pH and calcium content are reviewed annually during the plant growing season to replenish and maintain these levels. By inoculating the mixed inoculant with arbuscular mycorrhizal fungi and adding calcium carbonate powder, the present invention promotes a K-based strategy in the microbial community, improving microbial carbon utilization efficiency and residual carbon formation efficiency, and facilitating soil organic carbon accumulation. Mineral protection of calcium further enhances soil organic carbon stability. The method significantly improves the carbon sink capacity of karst soils still in the young and middle forest stages.

Description

Technical Field

[0001] The present invention relates to the technical field of karst carbon sequestration and sink enhancement, and more specifically to a method for promoting the accumulation of organic carbon in karst soil, belonging to the field of soil ecology. Background Art

[0002] Although soil is the largest carbon pool in terrestrial ecosystems, the carbon sequestration capacity of karst soil is significantly lower than that of vegetation. This is mainly due to the following reasons: (1) the karst bedrock is widely exposed, the soil layer is generally shallow and discontinuous, and the total amount of soil carbon pool is relatively small; (2) due to the geological background of the karst area, which is characterized by a lack of soil and stone, and a lack of both water and soil, the accumulation of regional vegetation carbon is accompanied by severe depletion of soil moisture and nutrients. A large amount of restored vegetation is still in the young and middle forest stage, and the contribution of vegetation photosynthetic carbon to soil organic carbon accumulation is relatively low.

[0003] Microorganisms are the engines driving the conversion of vegetation photosynthetic carbon into soil organic carbon. The products assimilated by soil microorganisms promote the formation and accumulation of soil organic carbon. Microbial carbon use efficiency (MCUE) refers to the efficiency with which microorganisms convert absorbed carbon into their own biomass carbon. Higher MCE means that, given a constant total carbon uptake, more carbon is used to build microbial biomass. Subsequently, upon microbial death, the assimilated carbon is returned to the soil as residues, thereby promoting soil organic carbon accumulation. R-strategy microorganisms tend to thrive in unstable, resource-rich environments, while K-strategy microorganisms typically thrive in resource-limited, relatively stable environments. Furthermore, K-strategy microorganisms typically have higher CUE, meaning they are more likely to promote soil organic carbon accumulation. Soil minerals, such as calcium, play a crucial role in soil organic carbon stabilization. For example, exchangeable calcium ions stabilize soil organic carbon by forming stable organic-inorganic complexes through inner and outer cation bridges. Calcium carbonate can stabilize soil organic carbon by promoting aggregate stability and can also directly contribute to soil organic carbon stabilization through adsorption and coating. Therefore, by changing the life history strategies of microorganisms (such as encouraging microorganisms to switch from r strategy to K strategy) and improving the mineral protection capacity of soil calcium, it helps to promote the stability and accumulation of organic carbon in karst soils.

[0004] Based on this, the patent of this invention promotes the change of soil microbial communities from the r strategy to the K strategy by inoculating mycorrhizal fungi. At the same time, by adding calcium carbonate, the mineral protection ability of calcium for soil organic matter is improved, which in turn creates an environment conducive to the growth of K strategy microorganisms. K strategy microorganisms have a high microbial carbon utilization efficiency, which promotes the accumulation of microbial residual carbon. The microbial residual carbon further combines with soil calcium through minerals to form an organic-inorganic complex, thereby improving the stability of soil organic carbon. The synergistic effect of comprehensive microorganisms and calcium promotes the stability and accumulation of soil organic carbon in a large number of karst vegetation in the middle and young forest stages. Summary of the Invention

[0005] In order to solve the problem of relatively slow accumulation of soil organic carbon in young forests in karst areas, the purpose of the present invention is to provide a method for promoting the accumulation of soil organic carbon in karst areas based on the synergistic effect of changes in microbial life history strategies and enhancement of calcium mineral protection capabilities, in order to increase the soil organic carbon content.

[0006] The technical solutions adopted by the present invention to achieve the above-mentioned purpose are as follows:

[0007] (1) Investigate soil pH and initial soil calcium content: Use a soil drill to randomly collect 10 soil samples from the 0-20 cm soil layer at the sample site to be investigated and mix them evenly. Pick out visible stones and roots, then pass through a 2 mm mesh sieve and bring them back to the laboratory for natural air drying before using them to determine soil pH and soil calcium carbonate content.

[0008] (2) Inoculation of arbuscular mycorrhizal fungi: Arbuscular mycorrhizal fungi belong to the K strategy microorganisms. Inoculation of arbuscular mycorrhizal fungi can help plants absorb water and nutrients in the soil, improve soil structure, and promote the stable development of soil K strategy microorganisms. Specifically, three arbuscular mycorrhizal inoculants were selected: Glomus mossesi, Glomus endoradici, and Glomus juvenile, and mixed them in a mass ratio of 1:1:1. Then, plants with well-developed root systems and no diseases were selected, and the mixed inoculant was buried in the soil near the roots. Each plant was inoculated with 20 g of the mixed inoculant near its roots.

[0009] (3) Add calcium carbonate to the soil: Add calcium carbonate powder according to the soil pH and soil calcium carbonate content of the current survey. When the soil pH is less than 6.5 and the soil calcium carbonate content is less than 1%, the amount of calcium carbonate powder added is 4 kg / m 2 When soil pH < 6.5 and soil calcium carbonate content < 2%, the amount of calcium carbonate powder added is 2 kg / m 2 When the soil pH is between 6.5 and 7 and the soil calcium carbonate content is between 2% and 3%, the amount of calcium carbonate powder added is 1 kg / m 2 When the soil pH is > 7 and the soil calcium carbonate content is ≥ 3%, there is no need to add additional calcium carbonate powder. The specific addition method is as follows: One month after the arbuscular mycorrhizal fungus inoculant is inoculated, choose a clear, rainless day and sprinkle the calcium carbonate powder directly onto the soil surface and then mix it into the soil.

[0010] (4) Maintain soil pH and calcium content: Investigate soil pH and calcium content annually during the plant growing season to ensure that the soil calcium carbonate content is ≥ 3% and the soil pH is > 6.5. If the pH and calcium content are lower than these values, add the corresponding weight of calcium carbonate powder as required in step (3).

[0011] The beneficial effects of the present invention are:

[0012] This invention utilizes the characteristic of arbuscular mycorrhizal fungi as K-strategy microorganisms. By inoculating these fungi, plants not only improve their utilization efficiency of soil water and nutrients but also promote the stability and growth of K-strategy microorganisms in the soil. Due to the humid environmental conditions of the southwestern karst region, the added calcium carbonate powder forms abundant exchangeable calcium ions and calcium carbonate deposits in the soil through dissolution and redeposition. These deposits stabilize soil organic carbon by forming organic-inorganic complexes through calcium ion bridging. Calcium carbonate also promotes soil organic carbon stability by promoting aggregate stability and adsorption and coating. This highly stable organic carbon environment, in turn, enhances the competitive advantage of K-strategy microorganisms within the soil microbial community. In other words, inoculating arbuscular mycorrhizal fungi and adding calcium carbonate powder strengthens the competitive advantage of K-strategy microorganisms within the soil microbial community. The K-strategy microorganisms achieve higher carbon utilization efficiency, increasing the efficiency of microbial residual carbon formation and promoting the contribution of microbial residuals to soil organic carbon accumulation. Furthermore, protected by exchangeable calcium ions and calcium carbonate, microbial residuals can remain stable and long-term in the soil. Therefore, the synergistic effect of microorganisms and soil calcium promotes the accumulation and stabilization of soil organic carbon. The method of the present invention increases the content of soil organic carbon by 10.1% and can be used in the field of soil carbon sequestration and sink enhancement. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 The increase in soil calcium content promotes the competitive advantage of K-strategy microorganisms;

[0014] Figure 2 is the relationship between microbial carbon utilization efficiency and microbial residual carbon accumulation;

[0015] Figure 3 Relationship diagram of soil organic carbon, microbial life history strategies, and soil calcium. DETAILED DESCRIPTION

[0016] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited by the specific embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0017] Example 1:

[0018] The research object is a shrub forest ecosystem in the middle and young forest stage of natural vegetation recovery in a typical karst area, and the area of ​​each sample plot is 20 m * 20 m.

[0019] 1. Investigate soil pH and initial soil calcium content: Use a soil drill to randomly collect 10 soil samples from the 0-20 cm soil layer at each plot and mix them evenly. Carefully pick out visible stones and roots in the soil samples. Then, sieve them through a 2 mm mesh and bring them back to the laboratory to air dry naturally before determining soil pH, calcium carbonate, and exchangeable calcium ion content. If conditions do not permit, the exchangeable calcium ion content of the soil may not be determined.

[0020] 2. Inoculation of Arbuscular Mycorrhizal Fungi: Three arbuscular mycorrhizal inoculants, Glomus mosseae, Glomus endoradiatus, and Glomus juvenile, were selected and mixed in a 1:1:1 ratio. Based on the vegetation survey results, five dominant shrub species were selected. Three well-growing shrubs of each dominant species were selected, relatively dispersed within the plot, ensuring that the entire plot was covered by the 15 selected shrubs. Subsequently, the soil around the taproot was carefully excavated along its growth direction using a shovel. The arbuscular mycorrhizal fungi mixture was inoculated into the fine roots. The excavated soil was backfilled with a shovel, maintaining the original unexcavated soil as closely as possible. Each plant's root system was inoculated with 20 g of the mixture, ensuring that the inoculant covered the entire plant. Since the soil pH in karst shrubland is typically between 6 and 7 and is free of human disturbance such as tillage and fertilization, this is generally conducive to the survival, growth, and root infection of arbuscular mycorrhizal fungi.

[0021] 3. Add calcium carbonate to the soil: One month after inoculating the arbuscular mycorrhizal fungi mixed inoculant, choose a sunny and rainless day to add calcium carbonate powder. The purpose of choosing one month after inoculating the arbuscular mycorrhizal fungi is to minimize the damage to the mycelial network in the early stage of inoculation due to human interference, thereby avoiding affecting the activity of the arbuscular mycorrhizal fungi. The amount of calcium carbonate added per square meter of the sample plot is determined based on the soil pH and initial calcium carbonate content investigated in step 1: ① When the soil pH is < 6.5 and the soil calcium carbonate content is < 1%, the amount of calcium carbonate powder added is 4 kg / m 2 ② When soil pH < 6.5 and soil calcium carbonate content < 2%, the amount of calcium carbonate powder added is 2 kg / m 2 ③ When the soil pH is between 6.5 and 7 and the soil calcium carbonate content is between 2% and 3%, the amount of calcium carbonate powder added is 1 kg / m 2④ When the soil pH is > 7 and the soil calcium carbonate content is ≥ 3%, there is no need to add additional calcium carbonate powder. To add calcium carbonate powder, first, pass the calcium carbonate powder through a 2 mm mesh to prevent particles from being too fine or too coarse. (This is because powdered calcium carbonate dissolves quickly in the soil, resulting in a faster effect but a shorter duration; larger particles dissolve slowly, resulting in a slower effect but a longer duration.) Then, sprinkle the calcium carbonate evenly on the soil surface and allow it to mix naturally with the soil without deep plowing. This is primarily because deep plowing disrupts the aggregate structure of karst soils, which is detrimental to the growth of mycorrhizal fungi and the soil's protection of organic carbon.

[0022] 4. Maintaining soil pH and calcium content: To ensure that the soil microbial community's life history strategy is dominated by the K strategy over the long term and to maintain the soil's high mineral protection capacity for calcium, it is necessary to ensure that the soil pH and calcium carbonate content are maintained at appropriate levels. This is because in karst areas with abundant rainfall but developed underground fissures and conduits, rainwater may wash away calcium carbonate on the soil surface and exchangeable calcium ions in the soil. However, it is also important to avoid excessive addition of calcium carbonate, as excessive calcium may interfere with the availability of other nutrients in the soil, such as phosphorus, thereby affecting plant nutrient requirements. Therefore, when the soil calcium carbonate content is ≥ 3% and the soil pH is > 6.5, no additional calcium carbonate supplementation is required; if it is below these values, the calcium carbonate addition rate should be based on the protocol in step 3.

[0023] Figure 1 The increase in soil calcium content promotes the competitive advantage of K strategy microorganisms

[0024] The relationship between different soil calcium levels and the ratio of bacterial K-strategy to r-strategy microorganisms was analyzed. Soil exchangeable calcium ions were measured by exchanging the collected soil with ammonium acetate and then measuring its content using inductively coupled plasma atomic emission spectrometry. Soil bacterial community structure was determined using MiSeq high-throughput sequencing. Soil DNA was extracted using the Fast DNA® SPIN kit according to the manufacturer's instructions. The 16S rRNA V4-V5 region of the bacterial gene was amplified using the primer pair 515F (5'-GTGCCAGCMGCCGCGGTAA-3') and 907R (CCGTCAATTCCTTTGAGTTT-3'). Acidobacteria, Actinobacteria, Planctomycetes, and Chloroflexi were classified as K-strategy microorganisms, while Firmicutes, Gemmatimonadetes, and Bacteroidetes were classified as r-strategy microorganisms. The ratio of bacterial K strategy to r strategy microorganisms = the sum of the relative abundances of K strategy microorganisms / the sum of the relative abundances of r strategy microorganisms. Figure 1 It can be seen that the ratio of the relative abundance of bacterial K strategy and r strategy microorganisms increased with the increase of soil exchangeable calcium ion content and reached a very significant level ( p < 0.001), which shows that the addition of calcium carbonate to the soil changed the structure of the soil microbial community from r strategy to K strategy microorganisms.

[0025] Figure 2 Figure 2 is the relationship between microbial carbon utilization efficiency and microbial residual carbon accumulation.

[0026] Microbial carbon utilization efficiency refers to the efficiency of microorganisms in converting absorbed carbon into their own biomass carbon. 18 O-H2O, after 24h of culture, CO2 concentration, DNA content, O content in DNA and 18O abundance was combined with microbial biomass carbon content to calculate microbial carbon utilization efficiency. Microbial residual carbon refers to the conversion of organic carbon into its own cellular components through microbial anabolism. Microbial residual carbon accumulates in the soil as microbial residues after microbial death and is an important source of soil organic carbon. The method for determining microbial residual carbon is as follows: amino sugar derivatives obtained through hydrolysis, purification, and derivatization were separated using an HP-5 gas chromatography capillary (30 m × 0.25 mm × 0.25 μm) and detected using a flame ionization detector. The contents of three amino monosaccharides (muramic acid, glucosamine, and galactosamine) were quantified based on peak area using the internal standard method. The carbon content of each amino monosaccharide, as well as the bacterial and fungal residual carbon content, was calculated based on the carbon atomic weight, number of carbon atoms, and molecular weight of the three amino monosaccharides.

[0027] Mineral-bound organic matter exists stably in the soil. Therefore, the higher the content of microbial residue carbon in the mineral-bound components, the better the stability of the microbial residue carbon, which is more conducive to promoting the accumulation of soil organic carbon. Figure 2 It can be seen that the content of microbial residual carbon in the mineral-bound fraction increased with the increase of microbial carbon utilization efficiency and reached a very significant level ( p < 0.001), indicating that higher microbial carbon utilization efficiency encourages microorganisms to contribute assimilated carbon sources to the soil carbon pool in the form of residues. Furthermore, microbial residue carbon is more easily incorporated into soil minerals, promoting both the accumulation and stability of soil organic carbon. K-strategy microorganisms have higher carbon utilization efficiency than r-strategy microorganisms. Therefore, when the microbial community is dominated by the K strategy, it is beneficial to the accumulation and stability of microbial residue carbon.

[0028] Figure 3 Relationship between soil organic carbon, microbial life history strategies, and soil calcium

[0029] Soil organic carbon content was determined by ferrous sulfate titration after oxidation with potassium dichromate and concentrated sulfuric acid. The ratio of bacterial K strategy to r strategy microorganisms and soil exchangeable calcium ion were determined using the same methods as above. Figure 3 As shown in a, soil organic carbon content increased with the increase in the ratio of K strategy microorganisms to r strategy microorganisms, and reached an extremely significant level ( p < 0.001), indicating that when the microbial community is dominated by the K strategy, it promotes the accumulation of soil organic carbon. Figure 3 b shows that soil organic carbon content increases with the increase of soil exchangeable calcium ions and also reaches a very significant level ( p< 0.001), indicating that increased soil calcium content also promoted the accumulation of soil organic carbon. Overall, soil organic carbon content was significantly increased when soil microorganisms adopted a K strategy and when soil calcium content increased, indicating that microorganisms and calcium synergistically promoted the accumulation of organic carbon in karst soils.

Claims

1. A method for promoting the accumulation of organic carbon in karst soil, comprising: (1) Investigate soil pH and initial soil calcium content; (2) Inoculate arbuscular mycorrhizal fungi, including: Glomus mosseae, Glomus endoradici, and Glomus juvenile, with equal mass mixtures. Each plant is inoculated with 20 g of the mixed inoculant near its root system. (3) Add calcium carbonate to the soil, including: When soil pH <6.5 and soil calcium carbonate content <1%, the amount of calcium carbonate powder added is 4kg / m 2 ; When soil pH <6.5 and soil calcium carbonate content <2%, the amount of calcium carbonate powder added is 2kg / m 2 ; When the soil pH is between 6.5 and 7, and the soil calcium carbonate content is between 2% and 3%, the amount of calcium carbonate powder added is 1kg / m 2 ; When the soil pH is greater than 7 and the soil calcium carbonate content is ≥3%, there is no need to add additional calcium carbonate powder; (4) Maintain soil calcium carbonate content ≥3% and soil pH > 6.

5.

2. The method according to claim 1, wherein: The investigation of soil pH and initial soil calcium content in step (1) includes: Ten soil samples from the 0-20 cm soil layer were randomly collected and mixed evenly. Stones and roots were picked out, and then the samples were sieved through a 2 mm mesh. After the soil samples were naturally air-dried, their pH value and calcium carbonate content were measured.

Images