Method for improving efficiency of phytoremediation of heavy metal contaminated soil and carbon fixation amount in process of phytoremediation of heavy metal contaminated soil through cooperation of organic acid and nitrification inhibitor

Abstract

The invention discloses a method for improving the efficiency of phytoremediation of heavy metal contaminated soil and the carbon immobilization amount in the process of phytoremediation of heavy metal contaminated soil through cooperation of organic acid and a nitrification inhibitor, and relates to the technical field of phytoremediation and greenhouse gas carbon sequestration and emission reduction. According to the method, organic acid (1 kg.ha-1 polyglutamic acid) and a nitrification inhibitor (10 kg.ha-1 dicyandiamide) are added in the phytoremediation period of the hybrid pennisetum, the growth index and biomass of the remediation plant hybrid pennisetum can be increased, the extraction amount of heavy metal Cd, Pb and Zn of the hybrid pennisetum can be effectively increased, meanwhile, emission of N2O in soil is slowed down in the phytoremediation process, and the yield of the hybrid pennisetum is increased. The carbon sequestration amount of plants is increased, and the method is very suitable for popularization and application in greenhouse gas emission reduction of the heavy metal contaminated soil.

Description

Technical Field

[0001] The present invention relates to the technical field of plant restoration of heavy metal soil and carbon fixation and emission reduction, and in particular to a method for improving the efficiency of plant restoration of cadmium (Cd), lead (Pb) and zinc (Zn) composite contaminated soil and the amount of carbon fixed in the process by using an organic acid (polyglutamic acid) in combination with a nitrification inhibitor (dicyandiamide). Background Art

[0003] Among various soil remediation technologies, phytoremediation technology has the advantages of low cost and environmental friendliness. This technology mainly plants plants with the ability to enrich heavy metals on soil contaminated by heavy metals such as Cd, Pb, and Zn. The heavy metals in the soil will be transferred to the plant body as the plant grows, and then it will be mowed or harvested to remove the heavy metals in the soil. This remediation technology is suitable for remediating large areas of contaminated soil. Different agronomic control measures can improve the remediation efficiency of plants. In addition, relevant studies have also shown that tillage patterns, water control, fertilization measures, soil texture, life activities of soil microorganisms, and plant planting and management methods will significantly affect the emission of greenhouse gases such as carbon dioxide (CO2) and nitrous oxide (N2O), which makes it feasible to reduce soil greenhouse gas emissions during the process of phytoremediation of heavy metal contaminated soil. Therefore, through different agronomic controls, a method to improve the efficiency of phytoremediation of heavy metal contaminated soil and the amount of carbon fixed in the process is explored, which will provide a reference for soil heavy metal remediation technology and carbon fixation and emission reduction technology.

[0004] At present, phytoremediation technology mainly focuses on improving efficiency, while greenhouse gas emission reduction technology mainly involves transportation and industry. There are few studies on reducing greenhouse gases in soil during phytoremediation. At the same time, existing greenhouse gas emission reduction technologies have problems such as unstable emission reduction effects, low economic benefits, and narrow application scope. Therefore, it is urgent to find a method that is both suitable for heavy metal contaminated soil and can increase carbon fixation during the remediation process. Summary of the invention

[0005] The purpose of the present invention is to provide a method for improving the efficiency of phytoremediation of heavy metal contaminated soil and the amount of carbon fixation in the process by using organic acids and nitrification inhibitors to address the technical problems existing in the current greenhouse gas emission reduction technology in the process of phytoremediation of heavy metal contaminated soil.

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

[0007] A method for improving the efficiency of plant repair of heavy metal contaminated soil and the amount of carbon fixed in the process by combining an organic acid with a nitrification inhibitor comprises adding polyglutamic acid and dicyandiamide during the process of plant repair of heavy metal contaminated soil to achieve the purpose of improving the efficiency of plant repair of heavy metals, reducing greenhouse gases in the soil and increasing carbon fixation.

[0008] In the above method, the organic acid is polyglutamic acid, which is added at the seedling stage and the mature stage, and the amount added each time is 1 kg·ha -1 .

[0009] In the above method, the nitrification inhibitor is dicyandiamide, which is added at the seedling stage and the mature stage, and the amount added each time is 10 kg·ha -1 .

[0010] In the above method, the greenhouse gases are carbon dioxide (CO2) and nitrous oxide (N2O).

[0011] In the above method, the heavy metal contaminated soil is cadmium (Cd), lead (Pb), and zinc (Zn) contaminated soil.

[0012] In the above method, the plant is hybrid Pennisetum.

[0013] The advantages of the present invention are that the implementation method only requires planting hybrid Pennisetum and adding polyglutamic acid and dicyandiamide during the restoration process, without the need for other treatment methods, and the operation is simple, convenient and low-cost. According to tests, the treatment time is within a short period of three months, the heavy metal restoration efficiency is improved, the soil greenhouse gas emissions are slowed down, and the carbon fixation amount in the restoration process is increased. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is a graph showing the plant height and yield of hybrid Pennisetum under different additive treatments.

[0015] Figure 2 shows the soil greenhouse gas CO2 emission flux under different additive treatments.

[0016] Figure 3 Figure 2 shows the soil greenhouse gas N2O emission flux under different additive treatments.

[0017] Figure 4 This is the accumulation diagram of soil greenhouse gas CO2 flux under different additive treatments.

[0018] Figure 5 This is the accumulation diagram of soil greenhouse gas N2O flux under different additive treatments.

[0019] Figure 6 Figure 2 shows soil organic carbon content under different additive treatments.

[0020] Figure 7 This is a graph showing the organic carbon content of hybrid Pennisetum and the cumulative CO2-C emissions from soil under different additive treatments.

[0021] Figure 8 This is a graph showing the amount of heavy metal Cd extracted from hybrid Pennisetum under different additive treatments.

[0022] Fig. 9 This is a graph showing the amount of heavy metal Pb extracted from hybrid Pennisetum under different additive treatments.

[0023] Fig.10 This is a graph showing the amount of heavy metal Zn extracted from hybrid Pennisetum under different additive treatments. DETAILED DESCRIPTION

[0024] The preferred embodiments of the present invention will be further described below in conjunction with the accompanying drawings.

[0025] Example:

[0026] 1. The soil in this embodiment is contaminated with heavy metals Cd, Pb and Zn in Si Village, Yangshuo County, Guilin City. The soil pH is 5.35, the soil Cd background value is 3.072 mg / kg, the soil Pb background value is 2453.0 mg / kg, and the soil Zn background value is 1329.0 mg / kg. According to the "Soil Environmental Quality Standard Agricultural Land Soil Pollution Risk Control Standard (Trial)" (GB15618-2018), the Cd, Pb and Zn contents of the soil far exceed the agricultural land soil pollution risk screening value, among which the Cd and Pb contents far exceed the agricultural land soil pollution risk control value, so the soil needs to be remediated for heavy metal pollution.

[0027] 2. Three treatments were set up, including no planting and no additives (CK0), planting hybrid Pennisetum (CK), and planting hybrid Pennisetum with polyglutamic acid and dicyandiamide (PGA+DCD), with three replicates for each treatment.

[0028] 3. Divide the farmland into 9 plots, each with an area of ​​2 m × 2 m, and the plots are separated by 0.5 m ridges.

[0029] 4. Transplant the hybrid Pennisetum seedlings that have been cultivated in the greenhouse for 15 days to the field and plant them at a density of 20-25 cm between each plant. After the hybrid Pennisetum has grown steadily for three days, apply 1 kg·ha of PGA+DCD to the plot by watering during the seedling stage (4th day) and the mature stage (70th day). -1 Polyglutamic acid and 10 kg·ha -1 Dicyandiamide, CK0 treatment and CK treatment were replaced with equal volumes of water. Field management during the planting process included daily watering, weeding and other measures.

[0030] 5. On the 0th, 15th, 30th, 45th, 60th, 75th, and 90th days after transplanting, soil greenhouse gases in all plots were collected using a syringe and a static box and the greenhouse gas emission flux was detected.

[0031] (1) The calculation formula for greenhouse gas emission flux is as follows:

[0032]

[0033] Where F is the gas emission flux (CO2 in mg·m -2 ·h -1 , the unit of N2O is μg·m -2 ·h -1 ); ρ is the gas density under standard conditions (kg·m -3 ); h is the height of the sampling box (m); dc / dt is the rate of change of gas concentration in the sampling box per unit time; T is the average temperature in the box during the sampling process (℃).

[0034] (2) The greenhouse gas emission flux results were fitted and integrated using the SCIPY library in Python to obtain the cumulative greenhouse gas emissions.

[0035] 6. After the last greenhouse gas collection on day 90, the hybrid Pennisetum was harvested and its growth indicators, plant height and yield, were measured. The plant samples were digested using the HNO3-H2O2 hot plate digestion method and the heavy metal content of the samples was determined using an inductively coupled plasma emission spectrometer.

[0036] 7. The plant height and yield of hybrid Pennisetum under different additive treatments are shown in Figure 1. The plant height, aboveground yield, root yield and total yield of PGA+DCD treatment were higher than those of CK treatment.

[0037] 8. The soil CO2 emission flux under different additive treatments is shown in Figure 2. There was no significant difference in the emission flux between the treatments in the first 30 days of planting. After 30 days, the CO2 emission flux of the PGA+DCD treatment continued to increase. At 90 days, the CO2 emission flux of the PGA+DCD treatment was significantly lower than that of the CK treatment.

[0038] 9. Soil N2O emission flux under different additive treatments Figure 3 As shown in the figure, the N2O emission fluxes of the CK treatment and the PGA+DCD treatment had the same trend from day 0 to day 60. The N2O emission flux of the PGA+DCD treatment was lower than that of the CK treatment in the first 30 days, and the N2O emission flux after 60 days was close to that of the CK and lower than that of the CK0 treatment.

[0039] 10. Cumulative emissions of soil CO2 and N2O under different additive treatments Figure 4 and Figure 5As shown in the figure, the cumulative emission of CO2 in CK treatment was not significantly different from that in CK0 treatment, and the cumulative emission of N2O in CK treatment was lower than that in CK0 treatment. The cumulative emission of CO2 in PGA+DCD treatment was higher than that in CK0 and CK treatment, while the cumulative emission of N2O in PGA+DCD treatment was lower than that in CK0 treatment, and there was no significant difference between PGA+DCD treatment and CK treatment.

[0040] 11. Soil organic carbon content under different additive treatments Figure 6 As shown, there was no significant difference in soil organic carbon content among the treatments.

[0041] 12. Organic carbon content of hybrid Pennisetum and cumulative CO2-C emission in soil under different additive treatments Figure 7 As shown in the figure, under the PGA+DCD treatment, the organic carbon content in the aboveground, roots and whole plant of hybrid Pennisetum and the cumulative CO2-C emission in the soil were higher than those in the CK treatment. The organic carbon content of the whole plant of hybrid Pennisetum under the PGA+DCD treatment was 92.62 g / m 2 The cumulative soil CO2-C emission is 20.86 g / m 2 The net carbon fixation is 71.76 g / m 2 .

[0042] 13. The extraction amount of heavy metals Cd, Pb and Zn in hybrid Pennisetum under different additive treatments Figure 8 , Fig. 9 and Fig.10 As shown in the figure, PGA+DCD treatment increased the extraction of Cd, Pb and Zn from the aboveground part, roots and whole plant of hybrid Pennisetum. Among them, PGA+DCD treatment significantly promoted the accumulation of Zn in the roots of hybrid Pennisetum.

[0043] 14. Therefore, the present invention plants hybrid Pennisetum in soil contaminated by Cd, Pb, and Zn, and simultaneously adds polyglutamic acid and dicyandiamide, which to a certain extent increases the plant height and yield of the repair plant hybrid Pennisetum, and increases the plant's extraction of Cd, Pb, and Zn. In the process of plant repair, the addition of polyglutamic acid and dicyandiamide does not increase the cumulative emission of N2O. Although the addition of polyglutamic acid and dicyandiamide will increase CO2 emissions, from the perspective of carbon fixation, the addition of polyglutamic acid and dicyandiamide does not significantly affect the soil organic carbon content (i.e., it has no significant effect on the soil carbon fixation), and the carbon fixation in the hybrid Pennisetum under this treatment can offset the soil carbon emissions, and its net carbon fixation is greater than zero. This shows that the method is very suitable for promotion for the repair of heavy metal contaminated soil and the reduction of greenhouse gas emissions. Without violating the essence of the present invention and the scope of the appended claims, appropriate changes can be made to some of the operational settings of the present invention during the implementation process.

Claims

1. A method for improving the efficiency of phytoremediation of heavy metal contaminated soil and the amount of carbon fixation in the process by combining an organic acid with a nitrification inhibitor, characterized in that Adding organic acids and nitrification inhibitors can slow down greenhouse gas emissions from heavy metal-contaminated soils, increase plant carbon sequestration and improve the efficiency of phytoremediation.

2. The method according to claim 1, characterized in that: The organic acid is polyglutamic acid, which is added at the seedling stage and the mature stage, and the amount added each time is 1 kg·ha -1 .

3. The method according to claim 1, characterized in that: The nitrification inhibitor is dicyandiamide, which is added at the seedling stage and the mature stage, and the amount added each time is 10 kg·ha -1 .

4. The method according to claim 1, characterized in that: The greenhouse gases are carbon dioxide (CO2) and nitrous oxide (N2O).

5. The method according to claim 1, characterized in that: The heavy metal contaminated soil is cadmium (Cd), lead (Pb) and zinc (Zn) contaminated soil.

6. The method according to claim 1, characterized in that: The plant is hybrid Pennisetum.

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