CN103698476A - Isotopic tracer method for determining carbon sources and carbon sinks of perennial vegetation in situ - Google Patents

Abstract

The invention discloses an isotope tracer method for in-situ determination of perennial vegetation carbon source carbon sink, which is characterized in that it is carried out according to the following steps: Step 1: measure the local air carbon dioxide concentration and record it as C0; Samples, get G1, G2, G3; Step 3: Collect gas recovery performance samples of the device, get G4, G5; Step 4: Collect local atmospheric carbon dioxide samples, get G6; Step 5: Perform steps 1 to 4 once a month ; Step 6: Carry out the carbon source and carbon sink calculation of C0 and G1, G2, G3, G4, G5, G6 obtained in the above steps, and obtain the annual respiration carbon amount per hectare of vegetation ( _year A, tons), annual net per hectare of vegetation The amount of fixed carbon ( _year B, tons) and the annual fixed carbon amount per hectare of vegetation ( _year D, tons). The beneficial effect of the invention is that the measuring method has high precision and simple operation.

Description

An Isotope Tracer Method for In Situ Determination of Carbon Source and Sink in Perennial Vegetation

technical field

The invention belongs to the technical field of environmental science and technology, and relates to an isotope tracer method for in-situ measurement of perennial vegetation carbon source and carbon sink.

Background technique

Human activities have led to a sharp increase in the concentration of carbon dioxide in the atmosphere, and the resulting greenhouse effect and global changes have attracted great attention from countries all over the world. The estimation of carbon sources and carbon sinks has become an important content in the study of adapting to global climate change and increasing sinks and reducing emissions. Scholars at home and abroad have done quantitative research on carbon sinks and carbon sources and their estimation methods. Among them, the carbon balance of terrestrial ecosystems is one of the core issues in global change science, and many research methods for carbon balance of terrestrial ecosystems have been established. The ground carbon isotope method is one of the most useful methods for analyzing terrestrial carbon balance, especially for exploring the dominant factors of terrestrial carbon balance and its response to global change. However, due to the complexity of terrestrial ecosystems, ground-based isotope methods extrapolate small-scale research results to regional or even global levels, which will cause large errors. At the same time, the ground isotope method mostly uses the micro-area marking method, and sets a specific area of micro-area for marking, and adds one to the calculation after sampling and measuring plants and soil. The operation is difficult, and it is not suitable for multi-micro-area measurement, especially measured in different seasons.

Contents of the invention

The purpose of the present invention is to provide an isotope tracer method for in-situ determination of carbon source and carbon sinks of perennial vegetation, which solves the problems of large error and complicated operation of the existing ground isotope method for determination of carbon source and carbon sinks.

Technical scheme of the present invention is to carry out according to the following steps:

Step 1: Measure the local air carbon dioxide concentration and record it as C0 (mg/L);

Step 2: Determination operation on the vegetation cover plot:

①Choose 5 representative plant-covered plots for the experiment, cover each plot with a bottomless plexiglass box, and perform the same operation on each glass box as follows: Dig a trench along the bottom of the box so that the bottom edge of the box is embedded in the soil 5cm , then cover with fine soil along the bottom of the box, compact it, open all air inlets and outlets, and balance for 15 minutes; ②Add 99% abundance, 1mg Na ₂ ¹³ CO ₃ Solid sample 1, record Na ₂ ¹³ CO ₃ solid sample 1 as G1, connect one of the air inlets of the bottomless plexiglass box to the gas generating device with a latex tube, close the other three air inlets and all gas outlets, and use Inject 5ml of 0.1N hydrochloric acid solution into the gas reaction bottle in the gas generating device with the syringe. After a few minutes, fill the gas reaction bottle with water through the external funnel in the gas generating device, discharge all the air, and close the air inlet connected to the gas generating device. switch, remove the gas generating device, empty the water in the gas reaction bottle in the gas generating device, and let the whole device stand still for 2 hours to make the vegetation in the bottomless plexiglass box carry out photosynthesis; ③ in the four gas absorbing devices Add 100g of ethanolamine to each gas receiving bottle, connect the four gas outlets of the bottomless plexiglass box with the four gas absorption devices with latex tubes, and connect the four vacuum pumps with the four gas absorption devices with rubber tubes; ④Start the vacuum pump and turn on all Switch the gas outlet to recover the gas. After 1 minute, turn on all the gas inlet switches. After about 15 minutes, turn off all the gas inlet and gas outlet switches, turn off the vacuum pump, and stop the recovery; ⑤Repeat the above ② and ④ every morning. times, the time is 6:00-8:00 and 8:30-10:30 respectively, repeat ② and ④ twice in the afternoon, the time is 13:00-15:00 and 15:30-17:30 respectively, in Turn on the vacuum pump from 18:00 in the afternoon to 6:00 in the morning of the next day, and open all the air inlets and outlets of the bottomless plexiglass box to continue to receive the gas. After 6:00 in the morning, remove the gas absorption device. At this time, all The liquid mixed sample in the gas receiving bottle is recorded as G2; ⑥ Replace all gas absorbing devices with new receiving bottles and receiving liquid, use latex tubes to connect the four gas outlets of the bottomless plexiglass box with the four gas absorbing devices, start the vacuum pump, Open all air inlets and air outlets until 6:00 in the morning of the third day, remove all gas absorption devices, record the liquid mixed sample in all gas receiving bottles as G3, and remove all devices;

Step 3: Appraisal of device gas recovery performance:

1) Carry out on a flat ground without plants, cover the bottomless plexiglass box, cover and compact with fine soil along the bottom edge, connect the gas generating device with a rubber hose at the air inlet, connect the gas receiving bottle at the air outlet, and open all the air inlets , gas outlet, and balance for 15 minutes; 2) add 99% abundance, 1 mg of Na ₂ ¹³ CO ₃ solid sample 2 to the gas reaction bottle in the gas generating device, and the Na ₂ ¹³ CO ₃ solid sample 2 at this time is recorded as G4, use a latex tube to connect one of the air inlets of the bottomless plexiglass box to the gas generator, close the other three inlet switches and all gas outlet switches, and inject 0.1N into the gas reaction bottle in the gas generator with a syringe Hydrochloric acid solution 5ml, after a few minutes, fill the gas reaction bottle with water through the external funnel in the gas generating device, discharge all the air, close the air inlet connected to the gas generating device, remove the gas generating device, and empty the gas generating device 3) add 100g ethanolamine to each of the gas receiving bottles in the four gas absorption devices, and connect the four gas outlets and the four gas outlets of the bottomless plexiglass box with latex tubes. Connect the absorption device, connect the four vacuum pumps with the four gas absorption devices with rubber hoses; 4) Start the vacuum pump, open all gas outlets, and perform gas recovery. After 1 minute, open all air inlets, and after about 15 minutes, close all air inlets. Turn off the vacuum pump at the air port and air outlet, and stop the recovery; 5) Repeat the above 2) and 4) twice a day in the morning, respectively, at 6:00-8:00 and 8:30-10:30, and repeat 2) in the afternoon and 4) twice each, at 13:00-15:00 and 15:30-17:30; turn on the vacuum pump during 18:00 in the afternoon of the same day-6:00 in the morning of the next day, and turn on the bottomless plexiglass All the air inlets and outlets of the box continue to receive gas, and the gas absorption device is removed after 6:00 in the morning. At this time, the liquid mixed sample in all gas receiving bottles is recorded as G5;

Step 4: Local Atmospheric Carbon Dioxide Collection:

Carry out on a flat ground without plants, cover the bottomless plexiglass box, cover and compact with fine soil along the bottom edge, connect the gas generating device with a rubber hose at the air inlet, connect the gas receiving bottle with the air outlet, and open all the air inlet and outlet Inlet, equilibrate for 15 minutes, add 100ml ethanolamine to the gas receiving bottle in the gas absorption device, connect the gas outlet and the gas absorption device with a latex tube, connect the vacuum pump to the gas absorption device with a rubber tube, open the gas outlet switch, start the vacuum pump, and carry out the gas Recovery, after about 15 minutes, stop the recovery, and record the liquid sample in the gas receiving bottle as G6;

Step 5: Steps 1 to 4 are carried out once in the middle of each month, and the experiment is carried out for 1 year;

Step 6: Carry out carbon source and carbon sink calculation:

Samples G1, G2, G3, G4, G5 and G6 were tested for carbon concentration respectively, and the measurement method used the existing technology and norms to calculate the total carbon content, which was respectively recorded as C1, C2, C3, C4, C5 and C6, and the unit was mg;

Samples G1, G2, G3, G4, G5 and G6 were respectively measured on the isotope ratio mass spectrometer for ¹³ C abundance, which were recorded as α1, α2, α3, α4, α5 and α6;

Calculation method of carbon source and carbon sink:

Calculation of device gas recovery rate:

β(%)=C5(α5-α6)/C4(α4-α6)×100

Tracer ¹³ C amount in one test:

χ1(mg)=C1(α1-α6),

The amount of tracer ¹³ C recovered on the first day per m ² vegetation:

χ2(mg)=C2(α2-α6)/β,

On the second day of the experiment, there was no ¹³ C labeling, and all the collected 13C was produced by respiration, so the amount of trace ¹³ C produced by respiration per m ² vegetation per day:

χ3(mg)=C3(α3-α6)/β,

Assuming that ¹² C and ¹³ C are not selective in photosynthetic fixation and respiration, the total amount of carbon represented by each mg of traced ¹³ C is:

φ(mg)=1000C0/χ1,

Among them, 1000 is the volume L of the plexiglass box, C0 is the atmospheric carbon concentration mg/L,

On the second day of the experiment, there was no ¹³ C mark, and all the collected 13 C was produced by respiration, so the amount of carbon respiration per m ² of vegetation per day is:

A=φ×χ3,

On the first day of the experiment, ¹³ C was fixed by plant photosynthesis, and ¹³ C was released by plant respiration at the same time, the difference between the traced ¹³ C amount χ1 in each experiment and the traced ¹³ C amount χ2 recovered per m ² vegetation on the first day The value is the amount of ¹³ C that is net fixed by vegetation per m ² per day, then the net carbon fixed by vegetation per m ² per day:

B=φ×(χ1-χ2),

The amount of carbon fixed by photosynthesis per ^m2 of vegetation per day is the sum of the net carbon amount of carbon fixed per ^m2 of vegetation per day and the respiration of carbon per ^m2 of vegetation in a day:

D＝φ×(χ1-χ2)+φ×χ3

The experiment is carried out once a month, and 12 times in 12 months of a year, then the average daily carbon respiration per m ² vegetation (A _average , mg), the average daily net fixed carbon amount per m ² vegetation (B _average , mg) and the average daily amount of carbon fixed by photosynthesis per m ² vegetation (D _average , mg) are:

A _average = (∑A)/12/5,

B _average = (∑B)/12/5,

D _average = (∑D)/12/5,

365 days per year, each hectare is 10000m ² , then the annual carbon respiration per hectare ( _year A, ton), the annual net fixed carbon per hectare ( _year B, ton) and the annual fixed carbon per hectare ( _year D , t) are:

A _year = 365×10 ^-9 A _average (tons/ha),

B _year = 365×10 ^-9 B _average (tons/ha),

_Year D = 365×10 ^-9 _Average B (tons/ha).

The beneficial effect of the invention is that the measuring method has high precision and simple operation.

Description of drawings

Fig. 1 is the structural representation of the bottomless plexiglass case of experimental device of the present invention;

Fig. 2 is the structural representation of experimental device gas absorption device of the present invention;

Fig. 3 is a schematic structural view of the gas generating device of the experimental device of the present invention.

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

1. Experimental device:

As shown in Figure 1, the bottomless plexiglass box (1m×1m×1m, that is, the length, width and height are 1m), the top four corners are 10cm away from the top edge, and the bottom four corners are 10cm away from the bottom edge. There are 4 air inlets and 4 The air outlet, the air inlet and the air outlet all have switches and can be connected with the outside world with rubber hoses.

The gas absorption device, as shown in Figure 2, has a gas receiving bottle 1 and a drying tower 2 filled with sodium hydroxide solids, the mouth of the gas receiving bottle 1 stretches out with two pipes, one of which is connected to the drying tower 2, The other one is used to connect the air outlet of the bottomless plexiglass box.

The gas generating device, as shown in Figure 3, has a gas reaction bottle 4 with a cork, and the cork center passes through two small glass tubes, one is connected to the funnel, and the other is used to connect the bottomless plexiglass box air inlet.

The vacuum pump 3, as shown in Fig. 2, is connected with the drying tower of the gas absorption device.

Reagents used:

Na ₂ ¹³ CO ₃

Hydrochloric acid solution (0.1N)

Ethanolamine, analytically pure

distilled water

2. Test method:

Step 1: Determination of local air carbon dioxide concentration (CO2):

It can be measured by conventional atmospheric carbon dioxide detector. Converted to carbon concentration, denoted as C0 (mg/L).

Step 2: Determination operation on the vegetation cover plot:

①Choose 5 representative plant-covered plots for the experiment, cover each plot with a bottomless plexiglass box, and perform the same operation on each glass box as follows: Dig a trench along the bottom of the box so that the bottom edge of the box is embedded in the soil 5cm , then cover with fine soil along the bottom of the box, compact it, open all air inlets and outlets, and balance for 15 minutes; ②Add 99% abundance, 1mg Na ₂ ¹³ CO ₃ Solid sample 1, record Na ₂ ¹³ CO ₃ solid sample 1 as G1, use a latex tube to connect one of the air inlets of the bottomless plexiglass box to the gas generating device, close the other three air inlets and all gas outlets, Use a syringe to inject 5ml of 0.1N hydrochloric acid solution into the gas reaction bottle 4 in the gas generating device. After a few minutes, fill the gas reaction bottle 4 with water through the external funnel in the gas generating device, discharge all the air, and close the gas generating device. The gas inlet switch is removed, the gas generating device is removed, and the water in the gas reaction bottle 4 in the gas generating device is emptied, and the whole device is left standing for 2h, so that the vegetation in the bottomless plexiglass box carries out photosynthesis; ③ in four gas Add 100g of ethanolamine to the gas receiving bottle 1 in the absorption device, connect the four gas outlets of the bottomless plexiglass box with the four gas absorption devices with latex tubes, and connect the four vacuum pumps 3 with the four gas absorption devices with rubber hoses; ④Start the vacuum pump 3, turn on all the gas outlet switches, and carry out gas recovery. After 1 minute, turn on all the gas inlet switches, and after about 15 minutes, turn off all the gas inlet and gas outlet switches, turn off the vacuum pump 3, and stop the recovery; ⑤Every day Repeat the above ② and ④ twice in the morning, the time is 6:00-8:00 and 8:30-10:30 respectively, repeat ② and ④ twice in the afternoon, the time is 13:00-15:00 and 15 :30-17:30, turn on the vacuum pump 3 from 18:00 in the afternoon of the same day to 6:00 in the morning of the next day, and open all the air inlets and outlets of the bottomless plexiglass box to continue to receive gas, after 6:00 in the morning Withdraw the gas absorption device, and record the liquid mixed sample in all gas receiving bottles 1 as G2 at this time; Connect the four gas absorption devices, start the vacuum pump 3, open all air inlets and gas outlets, until 6:00 in the morning of the third day, remove all gas absorption devices, record the liquid mixed sample in all gas receiving bottles 1 as G3, and withdraw remove all devices;

Step 3: Appraisal of device gas recovery performance:

1) Carry out on a flat ground without plants, cover the bottomless plexiglass box, cover and compact with fine soil along the bottom edge, connect the gas generating device with a rubber hose at the air inlet, connect the gas receiving bottle 1 at the air outlet, open all the inlet 2) Add 99% abundance, 1 mg of Na ₂ ¹³ CO ₃ solid sample 2 to the gas reaction bottle 4 in the gas generating device, and the Na ₂ ¹³ CO ₃ solid sample 2 at this time Denote it as G4, use a latex tube to connect one of the air inlets of the bottomless plexiglass box to the gas generator, close the other three inlet switches and all gas outlet switches, and use a syringe to inject gas reaction bottle 4 into the gas generator. Inject 5ml of 0.1N hydrochloric acid solution, and after a few minutes, fill the gas reaction bottle 4 with water through the external funnel in the gas generating device, discharge all the air, close the air inlet connected to the gas generating device, remove the gas generating device, and pour The water in the gas reaction bottle 4 in the air gas generating device, the whole device is left standstill for 2h; 3) each add 100g ethanolamine in the gas receiving bottle 1 in the four gas absorbing devices, and four bottomless plexiglass boxes are filled with latex tubes. The gas outlet is connected to the four gas absorption devices, and the four vacuum pumps 3 are connected to the four gas absorption devices with rubber hoses; 4) Start the vacuum pump 3, open all the gas outlets, and perform gas recovery. After 1 minute, open all the air inlets, After about 15 minutes, close all the air inlets and outlets, turn off the vacuum pump 3, and stop the recovery; 5) repeat the above 2) and 4) twice every morning, and the time is 6:00-8:00 and 8:30 respectively -10:30, repeat 2) and 4) twice in the afternoon, the time is 13:00-15:00 and 15:30-17:30 respectively; during the period from 18:00 in the afternoon of the same day to 6:00 in the morning of the next day Turn on the vacuum pump 3, and open all air inlets and air outlets of the bottomless plexiglass box, continue to receive the gas, remove the gas absorption device after 6:00 in the morning, and now all the liquid mixed samples in the gas receiving bottle 1 are recorded as G5;

Step 4: Local Atmospheric Carbon Dioxide Collection:

Carry out on a flat ground without plants, cover the bottomless plexiglass box, cover and compact with fine soil along the bottom edge, connect the gas generating device with a rubber hose at the air inlet, connect the gas receiving bottle 1 at the air outlet, open all the air inlet, At the gas outlet, balance for 15 minutes, add 100ml of ethanolamine to the gas receiving bottle 1 in the gas absorption device, connect the gas outlet and the gas absorption device with a latex tube, connect the vacuum pump 3 with the gas absorption device with a rubber tube, turn on the gas outlet switch, and start the vacuum pump 3. Carry out gas recovery, stop the recovery after about 15 minutes, and record the liquid sample in the gas receiving bottle 1 as G6;

Step 5: Steps 1 to 4 are carried out once in the middle of each month, and the experiment is carried out for 1 year;

Step 6: Carry out carbon source and carbon sink calculation:

Samples G1, G2, G3, G4, G5 and G6 were tested for carbon concentration respectively, and the measurement method used the existing technology and norms to calculate the total carbon content, which was respectively recorded as C1, C2, C3, C4, C5 and C6, and the unit was mg;

The ¹³ C abundance of samples G1, G2, G3, G4, G5, and G6 were measured on an isotope ratio mass spectrometer, respectively, and recorded as α1, α2, α3, α4, α5, and α6, and the unit is mg; carbon source and carbon sink calculation method :

Calculation of device gas recovery rate:

β(%)=C5(α5-α6)/C4(α4-α6)×100

Tracer ¹³ C amount in one test:

χ1(mg)=C1(α1-α6),

The amount of tracer ¹³ C recovered on the first day per m ² vegetation:

χ2(mg)=C2(α2-α6)/β,

There is no 13C label on the second day of the experiment, and all the collected ¹³ C is produced by respiration, so the amount of trace ¹³ C produced by respiration per m ² vegetation per day:

χ3(mg)=C3(α3-α6)/β,

Assuming that ¹² C and ¹³ C are not selective in photosynthetic fixation and respiration, the total amount of carbon represented by each mg of traced ¹³ C is:

φ(mg)=1000C0/χ1,

Among them, 1000 is the volume L of the plexiglass box, C0 is the atmospheric carbon concentration mg/L,

There was no ¹³ C mark on the second day of the experiment, and all the collected ¹³ C was produced by respiration, so the amount of carbon respiration per m ² of vegetation per day is:

A=φ×χ3,

On the first day of the experiment, ¹³ C was fixed by plant photosynthesis, and ¹³ C was released by plant respiration at the same time, the difference between the traced ¹³ C amount χ1 in each experiment and the traced ¹³ C amount χ2 recovered per m ² vegetation on the first day The value is the amount of ¹³ C that is net fixed by vegetation per m ² per day, then the net carbon fixed by vegetation per m ² per day:

B=φ×(χ1-χ2),

The amount of carbon fixed by photosynthesis per ^m2 of vegetation per day is the sum of the net carbon amount of carbon fixed per ^m2 of vegetation per day and the respiration of carbon per ^m2 of vegetation in a day:

D＝φ×(χ1-χ2)+φ×χ3

The experiment is carried out once a month, and 12 times in 12 months of a year, then the average daily carbon respiration per m ² vegetation (A _average , mg), the average daily net fixed carbon amount per m ² vegetation (B _average , mg) and the average daily amount of carbon fixed by photosynthesis per m2 vegetation (D _average , mg) are:

A _average = (∑A)/12/5,

B _average = (∑B)/12/5,

D _average = (∑D)/12/5,

365 days per year, each hectare is 10000m ² , then the annual carbon respiration per hectare ( _year A, ton), the annual net fixed carbon per hectare ( _year B, ton) and the annual fixed carbon per hectare ( _year D , t) are:

A _year = 365×10 ^-9 A _average (tons/ha),

B _year = 365×10 ^-9 B _average (tons/ha),

_Year D = 365×10 ^-9 _Average B (tons/ha).

The method of the present invention uses a specific marking device for in-situ marking, does not need to take samples of plants and soil, is simple to operate, can set more micro-areas at the same time, and is carried out according to different seasons, which is more representative, and the research results can be extrapolated It is more reliable to calculate the carbon source and carbon sink of the entire terrestrial ecosystem.

Claims (1)

1. an isotope tracer method for measuring perennial vegetation carbon source carbon sink in situ, is characterized in that carrying out according to the following steps: Step 1: Measure the local air carbon dioxide concentration and record it as C0 (mg/L); Step 2: Determination operation on the vegetation cover plot: ①Choose 5 representative plant-covered plots for the experiment, cover each plot with a bottomless plexiglass box, and perform the same operation on each glass box as follows: Dig a trench along the bottom of the box so that the bottom edge of the box is embedded in the soil 5cm , then cover with fine soil along the bottom of the box, compact it, open all air inlets and air outlets, and balance for 15 minutes; 2. add 99% abundance, 1mg Na in the gas reaction bottle (4) in the gas generating device ₂ ¹³ CO ₃ solid sample 1, record Na ₂ ¹³ CO ₃ solid sample 1 as G1, use a latex tube to connect one of the air inlets of the bottomless plexiglass box to the gas generating device, close the other three air inlets and all outlets. Gas port, use a syringe to inject 5ml of 0.1N hydrochloric acid solution into the gas reaction bottle (4) in the gas generating device, and after a few minutes, fill the gas reaction bottle (4) with water through the external funnel in the gas generating device, and discharge all the air , close the air inlet switch connected to the gas generating device, remove the gas generating device, empty the water in the gas reaction bottle (4) in the gas generating device, and let the whole device stand still for 2h, so that the vegetation in the bottomless plexiglass box is carried out Photosynthesis; 3. respectively add 100g ethanolamine in the gas receiving bottle (1) in the four gas absorption devices, connect the four gas outlets of the bottomless plexiglass box with the four gas absorption devices with latex tubes, connect the four Vacuum pump (3) is connected with four gas absorption devices; ④Start vacuum pump (3), open all gas outlet switches for gas recovery, after 1 minute, open all air inlet switches, after about 15 minutes, close all air inlets , gas outlet switch, turn off the vacuum pump (3), stop recycling; ⑤ Repeat the above ② and ④ twice every morning, the time is 6:00-8:00 and 8:30-10:30 respectively, repeat ② and ④ in the afternoon Twice each time, 13:00-15:00 and 15:30-17:30 respectively, turn on the vacuum pump (3) from 18:00 in the afternoon of the same day to 6:00 in the morning of the next day, and turn on the bottomless plexiglass All the gas inlets and outlets of the box continue to receive gas, and the gas absorption device is removed after 6:00 in the morning. At this time, the liquid mixed sample in all gas receiving bottles (1) is recorded as G2; ⑥Replace all gas absorption devices with new ones Receive the bottle and the receiving liquid, connect the four gas outlets of the bottomless plexiglass box with the four gas absorption devices with latex tubes, start the vacuum pump (3), and open all the air inlets and gas outlets until 6:00 in the morning of the third day , remove all gas absorption devices, record the liquid mixed sample in all gas receiving bottles (1) as G3, and remove all devices; Step 3: Appraisal of device gas recovery performance: 1) Carry out on a flat ground without plants, cover the bottomless plexiglass box, cover and compact with fine soil along the bottom edge, connect the gas generating device with a rubber hose at the air inlet, connect the gas receiving bottle (1) at the air outlet, and open All inlets and outlets are equilibrated for 15 minutes; 2) Add 99% abundance, 1 mg of Na ₂ ¹³ CO ₃ solid sample 2 to the gas reaction bottle (4) in the gas generating device, and the Na ₂ ¹³ CO 3 solid sample 2 at this time is ₃ Solid sample 2 is marked as G4, connect one of the air inlets of the bottomless plexiglass box to the gas generating device with a latex tube, close the other three inlet switches and all gas outlet switches, and use a syringe to inject gas into the gas generating device. Inject 5ml of 0.1N hydrochloric acid solution into the gas reaction bottle (4), and after a few minutes, fill the gas reaction bottle (4) with water through the external funnel in the gas generating device, discharge all the air, and close the air inlet connected to the gas generating device , remove the gas generating device, empty the water in the gas reaction bottle (4) in the gas generating device, and let the whole device stand for 2h; 3) add 100g ethanolamine to each of the gas receiving bottles (1) in the four gas absorbing devices , connect the four gas outlets of the bottomless plexiglass box with the four gas absorption devices with latex tubes, and connect the four vacuum pumps (3) with the four gas absorption devices with rubber tubes; 4) Start the vacuum pump (3), open all outlets Air port for gas recovery. After 1 minute, open all air inlets. After about 15 minutes, close all air inlets and air outlets, turn off the vacuum pump (3), and stop the recovery; 5) Repeat the above 2) and 4) every morning 2 times each, the time is 6:00-8:00 and 8:30-10:30 respectively, repeat 2) and 4) twice in the afternoon, the time is 13:00-15:00 and 15:30-17 :30; Turn on the vacuum pump (3) during the period from 18:00 in the afternoon to 6:00 in the morning of the next day, and open all the air inlets and outlets of the bottomless plexiglass box to continue to receive the gas, and remove it after 6:00 in the morning Gas absorption device, at this time, the liquid mixed samples in all gas receiving bottles (1) are recorded as G5; Step 4: Local Atmospheric Carbon Dioxide Collection: Carry out on a flat ground without plants, cover the bottomless plexiglass box, cover and compact with fine soil along the bottom edge, connect the gas generating device with a rubber hose at the air inlet, connect the gas receiving bottle (1) at the air outlet, and open all the inlets Gas, gas outlet inlet, equilibrate for 15 minutes, add 100ml ethanolamine to the gas receiving bottle (1) in the gas absorption device, connect the gas outlet and the gas absorption device with a latex tube, connect the vacuum pump (3) to the gas absorption device with a rubber tube, and open Switch the gas outlet, start the vacuum pump (3), and carry out gas recovery. After about 15 minutes, stop the recovery, and record the liquid sample in the gas receiving bottle (1) as G6; Step 5: Steps 1 to 4 are carried out once in the middle of each month, and the experiment is carried out for 1 year; Step 6: Carry out carbon source and carbon sink calculation: Samples G1, G2, G3, G4, G5 and G6 were tested for carbon concentration respectively, and the measurement method used the existing technology and norms to calculate the total carbon content, which was respectively recorded as C1, C2, C3, C4, C5 and C6, and the unit was mg; Samples G1, G2, G3, G4, G5 and G6 were respectively measured on the isotope ratio mass spectrometer for ¹³ C abundance, which were recorded as α1, α2, α3, α4, α5 and α6; Calculation method of carbon source and carbon sink: Calculation of device gas recovery rate: β(%)=C5(α5-α6)/C4(α4-α6)×100 Tracer ¹³ C amount in one test: χ1(mg)=C1(α1-α6), The amount of tracer ¹³ C recovered on the first day per m ² vegetation: χ2(mg)=C2(α2-α6)/β, There is no ¹³ C mark on the second day of the experiment, and the collected ¹³ C is all produced by respiration, so the amount of trace ¹³ C produced by respiration per m ² vegetation per day: χ3(mg)=C3(α3-α6)/β, Assuming that ¹² C and ¹³ C are not selective in photosynthetic fixation and respiration, the total amount of carbon represented by each mg of traced ¹³ C is: φ(mg)=1000C0/χ1, Among them, 1000 is the volume L of the plexiglass box, C0 is the atmospheric carbon concentration mg/L, There was no ¹³ C mark on the second day of the experiment, and all the collected ¹³ C was produced by respiration, so the amount of carbon respiration per m ² of vegetation per day is: A=φ×χ3, On the first day of the experiment, ¹³ C was fixed by plant photosynthesis, and ¹³ C was released by plant respiration at the same time, the difference between the traced ¹³ C amount χ1 in each experiment and the traced ¹³ C amount χ2 recovered per m ² vegetation on the first day The value is the net fixed amount of ¹³ C per m2 of vegetation per day, then the net fixed amount of carbon per ^m2 of vegetation per day: B=φ×(χ1-χ2), The amount of carbon fixed by photosynthesis per ^m2 of vegetation per day is the sum of the net carbon amount of carbon fixed per ^m2 of vegetation per day and the respiration of carbon per ^m2 of vegetation in a day: D＝φ×(χ1-χ2)+φ×χ3 Then the average daily carbon respiration per m ² of vegetation (A _average , mg), the average daily net fixed carbon per m ² vegetation (B _average , mg) and the average daily carbon fixed by photosynthesis per m ² vegetation (D _average , mg) are: A _average = (∑A)/12/5, B _average = (∑B)/12/5, D _average = (∑D)/12/5, 365 days per year, each hectare is 10000m ² , then the annual carbon respiration per hectare ( _year A, ton), the annual net fixed carbon per hectare ( _year B, ton) and the annual fixed carbon per hectare ( _year D , t) are: A _year = 365×10 ^-9 A _average (tons/ha), B _year = 365×10 ^-9 B _average (tons/ha), _Year D = 365×10 ^-9 _Average B (tons/ha).

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