Rhizobox system and testing method for in-situ testing of rhizosphere microzone of aquatic plants

Abstract

The application discloses a rhizobox system and a testing method for in-situ testing of aquatic plant rhizosphere microzones, which comprises a rhizobox, an in-situ testing device, a water tank, an aeration device and a water tank water circulation device; the in-situ testing device comprises a DGT probe, a circular DGT, a detection film, a interstitial water sampler and a soil solution sampler; the rhizobox is internally provided with an overlying water layer, a root chamber and a sediment chamber, the side wall of the root chamber is provided with a first testing port, a second testing port and a first sampling port, the first testing port is provided with a detachable flat plate, the inner side of the flat plate is used for attaching the detection film, the side wall of the sediment chamber is provided with a third testing port and a second sampling port, the water tank is provided with an illumination device above, the aeration device is used for aerating the water tank, the water tank water circulation device is communicated with both ends of the water tank to form a circulation loop, the water tank is provided with a light-transmitting top cover, the rhizobox is used for being hung in the water tank, and the water tank is provided with an electrode probe. The application can realize in-situ testing of multiple types of root zones and accurate collection of sediment samples.

Description

Technical Field

[0001] This invention relates to the fields of lake water ecological restoration and in-situ testing technology, and in particular to a root box system and testing method for in-situ testing of rhizosphere micro-regions of aquatic plants. It is used to study the nitrogen and phosphorus migration and absorption process in the rhizosphere of aquatic plants, the nitrogen and phosphorus remediation mechanism of rhizosphere sediments, and to verify and evaluate the ecological restoration capacity of different aquatic plants for polluted sediments. Background Technology

[0002] Phytoremediation technology can be used for aquatic ecosystem restoration, and commonly used plants include submerged plants, emergent plants, floating-leaved plants, and free-floating plants. Aquatic plant sediment remediation technology is relatively low-cost, primarily removing or reducing pollutant content in sediments through plant absorption. Submerged plants, in particular, mainly absorb nutrients from bottom sediments, where nutrients are several orders of magnitude higher than water-soluble nutrients. Nutrients are removed from the lake when aquatic plants are harvested, significantly reducing nutrient levels in the lake water and the endogenous load on sediments. Large aquatic plants can release oxygen from their roots, forming a root oxidation zone that transforms the rhizosphere sediment from an anaerobic to an aerobic state, preventing sediment uplift caused by anaerobic decomposition of organic matter. Root oxygenation (ROL) refers to the process by which aquatic plants transport photosynthetically produced oxygen to the roots through aerenchyma tissues such as rhizomes and release it radially into the rhizosphere sediment via the root axis. Part of the root oxygenation is used to meet root respiration, and another part is released radially into the rhizosphere through the root neck, creating a micro-oxygen environment in the root zone that facilitates pollutant degradation. Aquatic plant rhizospheres play a crucial role in the extraction of nitrogen and phosphorus from sediments. Understanding the geochemical and ecological restoration mechanisms of rhizosphere uptake and the migration of nitrogen, phosphorus, and heavy metals is essential, including: ① the complex multi-element coupled biogeochemistry of the aquatic plant rhizosphere; ② the spatial variation characteristics of the rhizosphere / sediment interface environmental parameters (DO / pH); and the influence of rhizosphere environmental parameters on rhizosphere nitrogen and phosphorus uptake and environmental behavior; ③ the influence of rhizosphere organic matter, root exudates, and root surface iron films on the bioavailability and migration processes of nitrogen, phosphorus, and heavy metals in rhizosphere sediments; and ④ the uptake capacity of aquatic plant rhizosphere for nitrogen, phosphorus, and heavy metals from sediments. A comprehensive understanding of the ecological restoration mechanisms of aquatic plants can provide theoretical support for lake sediment pollution control engineering.

[0003] Root chambers and in-situ sampling or testing techniques, including gradient diffusion film (DGT) technology, planar optical (PO) technology, pore water sampler (Peeper), soil solution sampler (Rhizon), and combinations of the above devices and techniques, can accurately obtain the spatial distribution characteristics of rhizosphere environmental parameters (DO / pH), elemental diffusion flux in rhizosphere sediment pore water, DGT concentration profiles in root surface sediments and non-rhizosphere sediments, sediment pore water concentration profiles, and collect pore water from rhizosphere sediments. They can also collect samples from rhizosphere sediments, non-rhizosphere sediments, and aquatic plant roots, stems, and leaves. Based on these experiments, we can profoundly reveal the geochemical processes involving multi-element coupling in the rhizosphere of aquatic plants, the kinetic mechanisms of nitrogen, phosphorus, and heavy metal absorption and migration in the rhizosphere, the influence mechanism of environmental parameters (DO / pH) on the migration and absorption of elements in the rhizosphere, the bioavailability of elements in the rhizosphere, and assess the absorption capacity of aquatic plants.

[0004] Currently, root chambers are mainly used for plant-soil and aquatic plant-sediment systems, as well as for verifying and evaluating the aquatic ecological restoration mechanisms and extraction capabilities of aquatic plants. In-situ sampling techniques—gradient diffusion film (DGT)—can obtain high-resolution 1D profiles and 2D images of rhizosphere elements, while planar photodynamic (PO) technology can test high-resolution 2D images of rhizosphere pH / DO. Peeper samplers are used to test 1D profiles of pore water concentration in the rhizosphere or main sediment, and Rhizons are used to extract pore water from sediment or the rhizosphere. Cultivating aquatic plants in root chambers and obtaining 2D distributions of micro-area elements / environmental parameters in the rhizosphere and main sediment using in-situ testing techniques such as DGT is an advanced experimental method for studying the ecological restoration mechanisms of aquatic plants; research literature has already reported on the above studies. Three types of root chambers are currently used for DGT testing in the rhizosphere of aquatic plants. However, the first type of root box in the aforementioned invention patent is equipped with three chambers and three filters, suitable for testing circular DGT in rhizosphere sediments and sampling rhizosphere sediments; used to study the phosphorus kinetics absorption-migration characteristics of aquatic plant rhizosphere. The second type of root box is used for testing circular DGT in aquatic plant roots and estimating phosphorus absorption; it is equipped with three filters, three chambers, the second chamber is divided into an inner chamber and an outer chamber, a detection port for the DGT detection device, a liquid delivery pipe, and a storage bottle. The third type of root box is used for DGT testing in the rhizosphere of aquatic plants, and can obtain high-resolution 2D images of phosphorus, iron, and sulfur. In addition to being used for aquatic plant cultivation, the main innovation of the root box is that the test chamber is equipped with a first slot for inserting the first insert / DGT probe and a second slot for inserting the second insert. The DGT probe is inserted into the first slot, and then the second insert is slowly removed, so that the main root and sediment originally attached to the second insert can be attached to the surface of the DGT probe in their original positions, completing the DGT test. The adsorption membrane is then removed for subsequent 2D analysis of the elements fixed by the DGT adsorption membrane. Another type of root box is used for testing the rhizosphere of aquatic or soil plants using fluorescent sensing membranes or a combination of DGT adsorption membranes and fluorescent sensing membranes. The root box is rectangular with a removable glass plate on one side. For DGT testing of root sediments, the glass plate can be removed, the aforementioned sensing membrane can be attached to the inner surface of its side wall, and the glass plate can be reinstalled so that it is in close proximity to the rhizosphere or sediment for membrane testing. Of the four types of root boxes mentioned above, the first two are used for testing circular DGT in the rhizosphere and cannot be used for testing DGT probes or fluorescent sensing membranes (PO). They are mainly used to study the absorption-migration kinetics of elements such as phosphorus in rhizosphere sediments or to assess ecological restoration capacity, and cannot obtain 2D images of multiple elements and environmental parameters. The third and fourth types of root boxes can only be used for testing the rhizosphere with DGT probes or DGT adsorption membranes / fluorescent sensing membranes and cannot perform circular DGT testing.None of the above four types of root boxes can complete the Peeper or Rhizon test; and their simple structure makes it impossible to collect sediment samples at different distances from the root system, such as root surface sediment (2 mm), rhizosphere sediment (4 mm), and main body sediment.

[0005] In summary, existing root boxes and experimental methods for in-situ testing of aquatic plant rhizosphere are too simple in structure and limited in function, failing to support the application of multiple in-situ testing techniques or accurately collect various sediment samples from different locations within the rhizosphere. Therefore, a novel root box is needed to cultivate aquatic plants in a simulated real lake environment, enabling in-situ testing of circular DGT and DGT probes, fluorescent sensing gels or DGT adsorption membranes, and Peeper or Rhizon assays in different rhizosphere regions, while simultaneously allowing for accurate collection of rhizosphere sediments. Based on the aforementioned root box and in-situ rhizosphere testing data, a theoretical foundation can be provided for research on rhizosphere elemental environmental processes and the assessment of ecological restoration capabilities in aquatic plants. Summary of the Invention

[0006] The purpose of this invention is to provide a root box system and testing method for in-situ testing of rhizosphere micro-regions of aquatic plants, so as to solve the problems existing in the prior art and realize various in-situ tests of the root zone and accurate collection of sediment samples.

[0007] To achieve the above objectives, the present invention provides the following solution:

[0008] This invention provides a root box system for in-situ testing of rhizosphere micro-regions of aquatic plants, including a root box, an in-situ testing device, a water tank, an aeration device, and a water tank water circulation device;

[0009] The in-situ testing device includes a DGT probe, a circular DGT, a detection membrane, a pore water sampler, and a soil solution sampler.

[0010] The root chamber is equipped with a first filter screen at the bottom. Inside the root chamber, there is an upper overlying water layer and a root chamber and a sediment chamber located below the overlying water layer. The root chamber and the sediment chamber are separated by a second filter screen and a third filter screen arranged at intervals. The side wall of the root chamber is provided with a first test port, a second test port, and multiple first sampling ports. The first test port is provided with a detachable plate, and the inner side of the plate is used to attach the detection membrane. The side wall of the sediment chamber is provided with a third test port and multiple second sampling ports. The second test port and the third test port are respectively used to put the circular DGT into the root chamber and the sediment chamber or to remove the circular DGT from the root chamber and the sediment chamber. The first sampling port and the second sampling port are respectively used to connect to the soil solution sampler. The DGT probe and the pore water sampler are used to insert into the root chamber from above the root chamber.

[0011] A lighting device is installed above the water tank to simulate sunlight. An aeration device is used to aerate the water tank. A water circulation device is connected to both ends of the water tank to form a circulation loop. A light-transmitting top cover is provided on the water tank to seal the opening at the top of the water tank. The root box is used to suspend in the water tank. An electrode probe is provided on the water tank to extend into the root box.

[0012] Preferably, the aeration device includes an aeration head, an air pump, and an air storage cylinder. One aeration head is installed at each end of the water tank. Each aeration head is connected to the main aeration pipe through an aeration branch pipe. The main aeration pipe is connected to the air pump. The air storage cylinder is connected to the main aeration pipe. A flow meter, a control valve, and a pressure reducing valve are also installed on the main aeration pipe between the air storage cylinder and the aeration branch pipe.

[0013] Preferably, the water tank water circulation device includes a return water tank and a peristaltic pump. One end of the water tank is connected to the return water tank through a return pipe, and the other end is connected to the outlet end of the peristaltic pump through an inlet pipe. The return water tank and the inlet end of the peristaltic pump are connected through a pipeline.

[0014] Preferably, the upper end of the water tank is provided with a crossbar, the electrode probe is connected to the crossbar through an aluminum alloy ruler, and the root box is suspended on the crossbar by a cable.

[0015] Preferably, the detection membrane includes a fluorescence sensing membrane and a DGT adsorption membrane, and the fluorescence sensing membrane is attached to the inner side of the plate, or both the fluorescence sensing membrane and the DGT adsorption membrane are attached simultaneously.

[0016] Preferably, the root box and the plate are both made of transparent plexiglass; the water tank is made of opaque plexiglass; the first filter, the second filter and the third filter are made of nylon with a pore size of 30μm.

[0017] Preferably, the light-transmitting top cover includes a top cover frame and a plastic film fixedly covering the top cover frame.

[0018] Preferably, the gas in the gas storage cylinder is argon or pure oxygen.

[0019] Preferably, both ends of the second filter and the third filter are fixed to the inner wall of the root box by plastic frames; a sealing cap is provided on the second test port and the third test port respectively for sealing the second test port and the third test port; each of the first sampling ports and each of the second sampling ports are sealed with rubber plugs.

[0020] This invention also provides an in-situ testing method for rhizosphere micro-regions of aquatic plants, based on the root box system for in-situ testing of rhizosphere micro-regions of aquatic plants described above, comprising the following steps:

[0021] (1) The sediments collected from the lake are dried, ground, sieved and mixed for pretreatment, and then lake water or tap water is added to make a paste.

[0022] (2) Lake water or tap water is introduced into the water tank through the water tank circulation device, and the water in the water tank is circulated back; according to the experimental requirements, a reagent or pollutant is added to the water tank circulation device, and the reagent or pollutant enters the water tank with the circulating water;

[0023] (3) Fill the root box evenly with the paste-like sediment, cut the stem of the aquatic plant seedling and insert it into the center of the root chamber, and cover the side wall of the root box with black plastic film.

[0024] (4) Suspend the root box in the water tank so that the root box is submerged below the water surface; insert the electrode probe into the root box and seal the upper opening of the water tank through the light-transmitting top cover;

[0025] (5) By adjusting the lighting device, the aeration device and the water circulation device of the water tank, the water environment parameters in the water tank are controlled to make them close to the environmental conditions of the lake; the aquatic plants grow stably for three months.

[0026] (6) In the later stage of aquatic plant growth, remove the root box, insert the DGT probe and the pore water sampler above the root chamber, and test the elemental profile of the root surface sediment in the root chamber; open the plate, attach the fluorescent sensing membrane or attach both the fluorescent sensing membrane and the DGT adsorption membrane, and then reinstall the plate; open the second test port and the third test port, place the circular DGT in the root surface sediment in the root chamber and the non-rhizosphere sediment in the sediment chamber respectively, and then close the second test port and the third test port; then place the root box back into the water tank.

[0027] (7) At the 8th hour, take out the root box, remove the black plastic film from the side wall of the root box, place the root box in the planar optical electrode test device, and immediately take out the fluorescent sensing film or the fluorescent sensing film and the DGT adsorption film after completing the fluorescence analysis of the fluorescent sensing film in the root chamber for subsequent DGT fixative analysis; reinstall and reset the plate, reattach the black plastic film to the side wall of the root box, and put the root box back into the water tank to reset it;

[0028] (8) At the 24th hour, the DGT probe and each of the circular DGTs were removed;

[0029] (9) At the 48th hour, the pore water sampler was removed and subsequent root surface sediment pore water analysis was performed.

[0030] (10) Connect the soil solution sampler to the first sampling port and the second sampling port, and take out the pore water sample from the root chamber and the sediment chamber;

[0031] (11) Take out the root box, take out the root surface deposits and aquatic plants in the root chamber, take out the rhizosphere deposits between the second filter and the third filter, take out the non-rhizosphere deposits in the deposit chamber, mix the rhizosphere deposits and non-rhizosphere deposits separately and then carry out subsequent processing.

[0032] (12) Separate the roots of aquatic plants from the sediment on the root surface, wash the roots clean, and separate the roots of aquatic plants from the parts above the roots for further processing.

[0033] (13) The gel strip eluent of the DGT probe, the adsorption membrane eluent of the circular DGT, the pore water sample obtained by the pore water sampler, the pore water sample obtained by the soil solution sampler, the DGT adsorption membrane, the aquatic plant root and above-root sample, and the sediment sample are analyzed and tested, and the environmental parameter data of the fluorescent sensing membrane are analyzed.

[0034] (14) Based on the analysis results and water environment parameters, study the geochemical reactions of rhizosphere elements, absorption-migration processes, and the influence mechanism of environmental parameters on rhizosphere processes of aquatic plants, and evaluate the water ecological restoration capacity of aquatic plants.

[0035] The present invention achieves the following technical effects compared to the prior art:

[0036] The root box system and testing method provided by this invention for in-situ testing of rhizosphere microregions of aquatic plants can perform in-situ testing of circular DGT and DGT probes, fluorescent sensing gels and DGT adsorption membranes, Peeper and Rhizon in different rhizosphere regions while simulating a real lake water environment and cultivating aquatic plants. At the same time, it can accurately collect rhizosphere sediments. Based on the root box and in-situ rhizosphere test data, a theoretical basis can be provided for the study of rhizosphere elemental environmental processes of aquatic plants and the assessment of their ecological restoration capabilities. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 This is a schematic diagram of the root box structure in this invention;

[0039] Figure 2 This is an exploded view of the root box in this invention;

[0040] Figure 3 This is a schematic diagram of the root box system for in-situ testing of rhizosphere micro-regions of aquatic plants provided by the present invention;

[0041] Figure 4 This is a schematic diagram of the structure of the fluorescent sensing membrane, DGT adsorption membrane and PVDF filter membrane attached to the inner side of the flat plate in this invention.

[0042] Figure 5 for Figure 4 Exploded view of the structure of the medium plate, the fluorescent sensing membrane, the DGT adsorption membrane, and the PVDF filter membrane;

[0043] Figure 6 This is a schematic diagram of the structure of the DGT probe in this invention;

[0044] Figure 7 This is a schematic diagram of the circular DGT structure in this invention;

[0045] Figure 8 This is a schematic diagram of the structure of the porous water sampler in this invention;

[0046] Figure 9 This is a schematic diagram of the soil solution sampler in this invention;

[0047] In the diagram: 1-Root box, 101-First filter screen, 102-Overlying water layer, 103-Root chamber, 104-Sediment chamber, 105-Second filter screen, 106-Third filter screen, 107-First test port, 108-Second test port, 109-First sampling port, 110-Plate, 111-Third test port, 112-Second sampling port, 113-Plastic frame;

[0048] 2-Water tank, 201-Crossbar;

[0049] 3-Aeration device, 301-Aeration head, 302-Air pump, 303-Gas storage cylinder, 304-Aeration branch pipe, 305-Aeration main pipe, 306-Flow meter, 307-Control valve, 308-Pressure reducing valve;

[0050] 4-Water tank circulation device, 401-Return water tank, 402-Peristaltic pump, 403-Return pipe, 404-Inlet pipe;

[0051] 5-DGT probe, 6-circular DGT, 7-pore water sampler, 8-soil solution sampler, 9-lighting device, 10-transparent top cover, 11-electrode probe, 12-aluminum alloy ruler, 13-cable, 14-fluorescent sensing membrane, 15-DGT adsorption membrane, 16-aquatic plant, 17-PVDF filter membrane. Detailed Implementation

[0052] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0053] The purpose of this invention is to provide a root box system and testing method for in-situ testing of rhizosphere micro-regions of aquatic plants, in order to solve the problems existing in the prior art and to realize various in-situ tests of the root zone and accurate collection of sediment samples.

[0054] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0055] like Figures 1-9 As shown, this embodiment provides a root box system for in-situ testing of rhizosphere micro-regions of aquatic plants, including a root box 1, an in-situ testing device, a water tank 2, an aeration device 3, and a water tank water circulation device 4.

[0056] The in-situ testing device includes a DGT probe 5, a circular DGT 6, a detection membrane, a pore water sampler 7, and a soil solution sampler 8;

[0057] A first filter screen 101 is installed at the bottom of the root box 1. Inside the root box 1, there is an upper overlying water layer 102 and a root chamber 103 and a sediment chamber 104 located below the overlying water layer 102. The root chamber 103 and the sediment chamber 104 are separated by a second filter screen 105 and a third filter screen 106 arranged at intervals. The side wall of the root chamber 103 is provided with a first test port 107, a second test port 108 and multiple first sampling ports 109. A detachable plate 110 is provided on the first test port 107. The inner side of the plate 110... For attaching the detection membrane, the sediment chamber 104 is provided with a third test port 111 and multiple second sampling ports 112 on its side wall. The second test port 108 and the third test port 111 are respectively used to put the circular DGT6 into the root chamber 103 and the sediment chamber 104 or to take out the circular DGT6 from the root chamber 103 and the sediment chamber 104. The first sampling port 109 and the second sampling port 112 are respectively used to connect the soil solution sampler 8. The DGT probe 5 and the pore water sampler 7 are used to insert the root box 1 from above the root chamber 103.

[0058] A light-emitting device 9 is installed above the water tank 2 to simulate sunlight. An aeration device 3 is used to aerate the water tank 2. A water circulation device 4 is connected to both ends of the water tank 2 to form a circulation loop. A light-transmitting top cover 10 is provided on the water tank 2 to seal the opening at the top of the water tank 2. A root box 1 is used to be suspended in the water tank 2. An electrode probe 11 is provided on the water tank 2 to extend into the root box 1.

[0059] The root box 1 and the plate 110 are both made of transparent plexiglass; the water tank 2 is made of opaque plexiglass; the first filter 101, the second filter 105, and the third filter 106 are made of nylon with a pore size of 30μm. A crossbar 201 is provided at the upper end of the water tank 2, and the electrode probe 11 is connected to the crossbar 201 via an aluminum alloy ruler 12. The root box 1 is suspended from the crossbar 201 by a cable 13. The light-transmitting top cover 10 includes a top cover frame and a plastic film fixedly covering the top cover frame. Both ends of the second filter 105 and the third filter 106 are fixed to the inner wall of the root box 1 by plastic frames 113; a sealing cap is provided on the second test port 108 and the third test port 111, respectively, for sealing the second test port 108 and the third test port 111; each first sampling port 109 and each second sampling port 112 is sealed with a rubber stopper. The detection membrane includes a fluorescent sensing membrane 14 and a DGT adsorption membrane 15. The fluorescent sensing membrane 14 or both the fluorescent sensing membrane 14 and the DGT adsorption membrane 15 are attached to the inner side of the plate 110.

[0060] The root box 1 is a cuboid with an internal space of 10cm in length, 8cm in width, and 12cm in height, made of 1.0cm thick plexiglass. Root chamber 103 is located on the right side of root box 1, measuring 3cm in length, 8cm in width, and 8cm in height. Sediment chamber 104 is located on the left side of root box 1, measuring 3cm in length, 8cm in width, and 8cm in height. A first filter screen 101 is horizontally installed at the bottom of root box 1, measuring 10cm in length and 8cm in width. A second filter screen 105 and a third filter screen 106 are vertically installed inside root box 1, measuring 8cm in width and 8cm in height. The second filter screen 105 is closer to root chamber 103, and the second and third filter screens are spaced 4mm apart. The sediment in root chamber 103 is surface sediment; the sediment between the second and third filter screens 105 and 106 is rhizosphere sediment; and the sediment in sediment chamber 104, extending more than 4mm outward from the third filter screen 106, is non-rhizosphere sediment. Aquatic plant 16 is placed in root chamber 103. The second filter 105 and the third filter 106 restrict the roots of the aquatic plant 16 to grow only in root chamber 103 and can distinguish between root surface deposits, rhizosphere deposits, and non-rhizosphere deposits. At the same time, the second filter 105 and the third filter 106 can also ensure the free migration of water, elements, and rhizosphere exudates between the chambers. The first filter 101 ensures that the sediment particles in root box 1 do not leak into the water body and allows water exchange between the water in the water tank 2 and the sediment in root box 1.

[0061] A first test port 107 is located in the center of the front wall of root chamber 103, and a plate 110 is installed thereon. The plate 110 is 2 cm wide and 6 cm high. A fluorescent sensing membrane 14 or a fluorescent sensing membrane 14 and a DGT adsorption membrane 15 can be attached to the inside of the plate 110 to test the 2D distribution image of elements and / or environmental parameters in root surface sediments. A second test port 108 with a diameter of 2.2 cm is located in the center of the rear wall of root chamber 103, and a plastic sealing cap is provided to seal the second test port 108. Five first sampling ports 109, or five small holes, with a diameter of 2.5 mm, are vertically opened in the center of the right side wall of root chamber 103. The vertical distance between each pair of small holes is 1 cm, and they are sealed with rubber stoppers. After removing the rubber stoppers, a soil solution sampler 8 can be connected.

[0062] A third test port 111 with a diameter of 2.2 cm is set in the center of the rear side wall of the sediment chamber 104, and a plastic sealing cap is provided to seal the third test port 111. Five second sampling ports 112, or five small holes with a diameter of 2.5 mm, are opened vertically in the center of the left side wall of the sediment chamber 104. The vertical distance between each pair of small holes is 1 cm, and they are sealed with rubber stoppers. After removing the rubber stoppers, the soil solution sampler 8 can be connected.

[0063] The water tank 2 is a cuboid with an internal space of 40cm long, 20cm wide, and 28cm high, made of 1.0cm thick plexiglass. Two crossbars 201, 1cm in diameter and 40cm long, are mounted on the top of the water tank 2. A 5-Star portable electrode probe 11 is connected to the crossbar 201 via an aluminum alloy scale 12. The probe's depth within the root chamber 1 and water tank 2 is controlled to measure the environmental parameters (pH / Eh / DO) of the water covering the root chamber 1 online. The vertical spatial resolution of the test is 1.0cm. The illumination device 9 uses a fluorescent tube. A fluorescent tube with a color temperature of 400K and a power of 150W, selected from Guangzhou Maiguang Electronics Technology Co., Ltd., is mounted on the crossbar 201 via a bracket. It closely approximates the solar spectrum and can automatically simulate sunlight, with an illumination intensity of 0–10000 Lux, or a fixed intensity can be set.

[0064] The aeration device 3 includes an aeration head 301, an air pump 302, and an air storage cylinder 303. One aeration head 301 is installed at each end of the water tank 2. Each aeration head 301 is connected to the main aeration pipe 305 via an aeration branch pipe 304. The main aeration pipe 305 is connected to the air pump 302. The air storage cylinder 303 is connected to the main aeration pipe 305 between the air storage cylinder 303 and the aeration branch pipe 304. A flow meter 306, a control valve 307, and a pressure reducing valve 308 are also installed on the main aeration pipe 305 between the air storage cylinder 303 and the aeration branch pipe 304. Two aeration branch pipes 304 are connected to the two ends of the crossbar 201. The aeration heads 301 below the aeration branch pipes 304 are placed in the water tank 2, and their depth in the water can be adjusted. The air pump 302 is a model 200-3702, selected from Eheim GmbH, Germany. It can aerate air, with a maximum exhaust volume of 400 L / min and a power of 3.5 W. The gas in gas cylinder 303 is argon or pure oxygen, and can provide argon or pure oxygen.

[0065] The translucent top cover 10 is a cuboid. The bottom of the cuboid top cover frame is not covered with plastic film, while all other sides are covered with plastic film. The translucent top cover 10 is 40cm long, 20cm wide, and 5cm high, used to seal the upper opening of the water tank 2, ensuring the anaerobic environment conditions of the water tank 2 and the root box 1. The plastic film is made of highly transparent and airtight EVA film with a thickness of 0.1mm. The frame of the cuboid top cover is made of rods with a diameter of 0.5cm. Five round holes are opened in the plastic film at the top of the translucent top cover 10, allowing passage for two aeration branch pipes 304, the fluorescent lamp support, the electrode probe 11, and the aluminum alloy ruler 12. The lower end of the plastic film on the side wall protrudes 1cm wide from the top cover frame. When it is necessary to seal the water tank 2, use waterproof tape to fix the 1cm wide plastic film to the four sides of the water tank 2. At the same time, the five round holes on the upper end of the plastic film are also sealed with waterproof tape. This will prevent leakage when nitrogen or argon is filled into the water tank 2, and maintain the stable anaerobic environment of the water in the water tank 2 and the root box 1.

[0066] The water circulation device 4 includes a return water tank 401 and a peristaltic pump 402. One end of the water tank 2 is connected to the return water tank 401 via a return pipe 403, and the other end is connected to the outlet of the peristaltic pump 402 via an inlet pipe 404. The return water tank 401 is connected to the inlet of the peristaltic pump 402 via a pipeline. The inlet pipe 404 is connected to the right side of the water tank 2 at a height of 26cm, and the return pipe 403 is connected to the left side of the water tank 2 at a height of 2cm. The outer diameter of the inlet pipe 404 and the return pipe 403 is 2cm, and the inner diameter is 1.5cm. They are made of PU (polyurethane) flexible tubing. The other end of the return pipe 403 is connected to the upper end of the return water tank 401. The return water tank 401 is 20cm long, 20cm wide, 15cm high, and has a wall thickness of 1.0cm. The other end of the pipeline connected to the inlet of the peristaltic pump 402 extends into the return water tank 401. The water circulation device 4 enables the water in the water tank 2 to circulate back, thereby simulating the water exchange and right-to-left flow in the water tank 2 to mimic the hydrodynamic conditions of a lake. Pollutants or agents (plant growth regulators) can be added to the return water tank 401 and circulated to the water bodies in the water tank 2 and root box 1 through the inlet pipe 404, simulating the concentration and chemical properties of pollutants in lake water and regulating plant growth.

[0067] A method for in-situ testing of rhizosphere micro-regions of aquatic plants, based on the root box system for in-situ testing of rhizosphere micro-regions of aquatic plants described above, includes the following steps:

[0068] (1) The sediments collected from the lake are dried, ground, sieved and mixed for pretreatment, and then lake water or tap water is added to make a paste.

[0069] (2) Lake water or tap water is introduced into the water tank 2 through the water tank water circulation device 4, and the water in the water tank 2 is circulated back; according to the experimental requirements, the reagents or pollutants are added to the water tank water circulation device 4, and the reagents or pollutants enter the water tank 2 with the circulating water.

[0070] (3) Fill the root box 1 evenly with the paste-like sediment, cut the stem of the aquatic plant 16 seedling and insert it into the center of the root chamber 103, and cover the side wall of the root box 1 with black plastic film.

[0071] (4) Suspend the root box 1 in the water tank 2 so that the root box 1 is submerged below the water surface; insert the electrode probe 11 into the root box 1 and seal the upper opening of the water tank 2 through the light-transmitting top cover 10.

[0072] (5) By adjusting the lighting device 9, the aeration device 3 and the water circulation device 4, the water environment parameters in the water tank 2 are controlled to make them close to the environmental conditions of the lake site; the aquatic plants 16 grow stably for three months.

[0073] (6) In the later stage of the growth of aquatic plant 16, remove root box 1, insert DGT probe 5 and pore water sampler 7 above root chamber 103, and test the elemental profile of root surface sediment in root chamber 103; open plate 110, attach fluorescent sensing film 14 or attach fluorescent sensing film 14 and DGT adsorption film 15 at the same time, and then reinstall plate 110; open second test port 108 and third test port 111, put circular DGT6 into root surface sediment in root chamber 103 and non-rhizosphere sediment in sediment chamber 104 respectively, and then close second test port 108 and third test port 111; then put root box 1 into water tank 2 and reinstall it.

[0074] (7) At the 8th hour, take out root box 1, remove the black plastic film on the side wall of root box 1, place root box 1 in the planar optical electrode test device, and immediately take out the fluorescent sensing film 14 or the fluorescent sensing film 14 and DGT adsorption film 15 after completing the fluorescence analysis in root chamber 103 for subsequent DGT fixative analysis; reinstall the reset plate 110, reattach the black plastic film on the side wall of root box 1, and put root box 1 back into water tank 2 to reset.

[0075] (8) At the 24th hour, remove the DGT probe 5 and each circular DGT 6;

[0076] (9) At the 48th hour, the pore water sampler 7 was removed and subsequent root surface sediment pore water analysis was performed.

[0077] (10) Connect the soil solution sampler 8 to the first sampling port 109 and the second sampling port 112 to take out the pore water samples from the root chamber 103 and the sediment chamber 104.

[0078] (11) Take out root box 1, take out root surface sediment and aquatic plants 16 in root chamber 103, take out rhizosphere sediment between second filter screen 105 and third filter screen 106, take out non-rhizosphere sediment in sediment chamber 104, mix rhizosphere sediment and non-rhizosphere sediment separately and then carry out subsequent treatment.

[0079] (12) Separate the roots of the 16 aquatic plants from the root surface sediment, wash the roots clean, and separate the roots of the 16 aquatic plants from the part above the roots for further processing.

[0080] (13) The gel strip eluent of DGT probe 5, the adsorption membrane eluent of circular DGT 6, the pore water sample obtained by pore water sampler 7, the pore water sample obtained by soil solution sampler 8, the DGT adsorption membrane 15, the root and above part of aquatic plant 16, and the sediment sample were analyzed and tested, and the environmental parameter data of fluorescent sensing membrane 14 were analyzed.

[0081] (14) Based on the analysis results and water environment parameters, study the geochemical reaction, absorption-migration process of rhizosphere elements of aquatic plant 16, the influence mechanism of environmental parameters on rhizosphere processes, and evaluate the water ecological restoration capacity of aquatic plant 16.

[0082] The following detailed description of the in-situ testing method for aquatic plant rhizosphere micro-regions according to the present invention includes the following steps:

[0083] (1) 2 kg of lake sediment with a total phosphorus content of 1000 mg / kg was collected from an area of ​​Hulun Lake in Inner Mongolia with a high eutrophication level and dried using a freeze dryer. The dried sediment was crushed, ground, and passed through an 80-mesh sieve. The mixture was then weighed. 4 L of water sample was collected from the same area of ​​Hulun Lake. Then, 0.4 kg of the dried sediment was mixed with 0.2 L of water sample to form a paste.

[0084] (2) Select two stems from the purchased Potamogeton crispus seedlings, each 10cm long and weighing about 12g.

[0085] (3) According to Figures 1-2 As shown, four plexiglass plates and three filters are assembled into root box 1 by fixing them with screws; the detachable plate 110 on the side wall of root chamber 103 is fixed with screws beforehand, the second test port 108 and the third test port 111 are sealed with plastic sealing caps, and each of the first sampling ports 109 and the second sampling port 112 is sealed with rubber stoppers. According to Figure 3 As shown, the water tank 2, crossbar 201, reflux tank 401, inlet pipe 404, reflux pipe 403, and peristaltic pump 402 are assembled into a whole. Water samples are poured into the water tank 2 and reflux tank 401, with the liquid level in the water tank 2 at 26 cm and the liquid level in the reflux tank 401 at 14 cm. The peristaltic pump 402 is started to achieve water reflux in both containers. According to experimental requirements, 15 mL of plant growth regulator (rooting powder), 2 mL of PO4-P stock solution (1 mg / L), and 2 mL of NH4-N stock solution (2 mg / L) are added to the reflux tank 401. The peristaltic pump 402 is adjusted to a speed of 140 r / min to ensure a certain flow rate (0.2 m / s) of liquid in the water tank 2 from right to left. Based on the difference between the predetermined pH value of water tank 2 and the pH value of the water covering the root chamber 103 of root box 1 measured by electrode probe 11, accurately calculate the volume of acid or alkali to be added, and add NaOH (5mol / L) or HCl (10mol / L) to the return water tank 401. First, add a volume slightly smaller than the amount of acid or alkali to be added; after the water is circulated and mixed, observe the pH value displayed online by electrode probe 11, and then add a small amount of acid or alkali solution to the return water tank 401 with a dropper until the pH value displayed by electrode probe 11 reaches the predetermined value.

[0086] (4) Carefully pour the water-added sediment sample into root chamber 103 and sediment chamber 104, evenly distribute it and at a height of 8cm; then insert the stems of two *Potamogeton crispus* plants into the sediment in root chamber 103 to a depth of 7cm, with the part above the roots 3cm exposed above the sediment in root chamber 103; fix the top of root box 1 to the upper crossbar 201 of water tank 2 with plastic cable 13, and suspend root box 1 in the middle of water tank 2, with root box 1 5cm from the bottom of water tank 2 and the top of root box 1 9cm from the liquid surface of water tank 2, so that the top of root chamber 103 is 13cm from the liquid surface of water tank 2.

[0087] Then, the four vertical round rods of the transparent plastic film top cover 10 are fixed to the top of the water tank 2. The 1cm wide EVA film covering the four side walls of the top of the water tank 2 is sealed with waterproof tape. The fluorescent tube bracket, aluminum alloy ruler 12, electrode probe 11, aeration branch pipe 304 and aeration head 301 are then fixed to the two horizontal rods 201 at the top of the water tank 2 through the five round holes on the transparent top cover 10. The electrode probe 11 is placed 12cm below the liquid surface of the water tank 2, directly above the sediment in the root chamber 103. The two aeration heads 301 are located in the water on both sides of the water tank 2 at a depth of 16cm. Then, the five round holes on the transparent plastic film top cover 10 are sealed with waterproof tape.

[0088] (5) According to Figure 3 Adjust the control panel of the fluorescent tube to simulate natural sunlight; start the electrode probe 11 to test the environmental parameters of the water covering the root chamber 103; assemble the air pump 302, gas cylinder 303 (nitrogen or argon), flow meter 306, control valve 307 and pressure reducing valve 308, connect the components through the aeration main pipe 305, and connect the aeration main pipe 305 to the aeration branch pipe 304; start the air pump 302 or the gas cylinder valve to aerate the water tank 2 at a flow rate of 0-120 mL / min; based on the environmental parameter DO and the predetermined DO value obtained by the electrode probe 11, control the control valve 307 to adjust the aeration rate, so that after the DO of the water covering the root chamber 1 reaches the predetermined value, continue aeration at a smaller aeration rate to keep the DO of the water covering the root chamber 1 stable.

[0089] (6) Keep the environmental and hydrodynamic conditions of the water tank 2 and root box 1 unchanged, so that the Potamogeton crispus can grow continuously in the root chamber 103 for more than 3 months, observe the root growth, and replenish water in time.

[0090] (7) When the *Potamogeton crispus* has grown for 3 months, remove the light-transmitting top cover 10, take out the root box 1, open the plate 110, and attach the DO fluorescent sensing membrane 14 + DGT adsorption membrane 15 (ZrO-AT adsorption membrane) and PVDF filter membrane 17 to the inner wall of the detachable plate 110; the DO+DGT sensing membrane is 1.6 cm wide and 5 cm high; then install the detachable glass plate 110 on the side wall of the root chamber 103, so that a section of the main root with deposits on the root surface is attached as much as possible to the surface of the PVDF filter membrane 17 of the sensing membrane; then open the second measuring... Test ports 108 and 111 are used to place a circular DGT6 probe into the root surface and non-rhizosphere sediments. Test ports 108 and 111 are then closed. The root box 1 is placed in the water tank 2. A DGT probe (ZrO-AT) and a pore water sampler 7 (Peeper) are inserted above the root chamber 103 and sediment chamber 104. The overlying water depth for the above tests is 4 cm, and the root surface sediment depth is 7 cm. This allows for the testing of ammonia nitrogen, nitrate nitrogen, and phosphorus profiles in the pore water of the root surface or non-rhizosphere sediments. The root box 1 is then returned to the water tank 2, and a transparent plastic film top cover 10 is installed above the water tank 2 and sealed with waterproof tape.

[0091] (8) At the 8th hour, remove the transparent plastic film top cover 10, take out root box 1, remove the black plastic film on the side wall of root box 1, place root box 1 in the planar photoelectric test device, and complete the fluorescence analysis of the fluorescence sensing membrane 14 inside the detachable glass plate 110 within three minutes to obtain a two-dimensional image of the dissolved oxygen concentration in the rhizosphere sediment. Immediately remove the detachable glass plate 110 from root box 1, take out the DO fluorescence sensing membrane + ZrO-AT adsorption membrane, cut the ZrO-AT adsorption membrane with a vertical resolution of 1 mm, and then elute with NaCl (1 mol / L) and NaOH (1 mol / L) solutions in sequence. Then, analyze the elemental concentration of the eluent using a micro spectrophotometer, that is, determine phosphorus by ammonium molybdate spectrophotometry, determine ammonia nitrogen by salicylic acid-hypochlorite colorimetry, and determine nitrate nitrogen by ultraviolet spectrophotometry. Calculate the DGT diffusion flux (ng / cm) based on the eluent concentration. 2 The profile distribution of / s).

[0092] (9) After removing the PO+DGT sensing film, immediately install the removable glass plate 110 to the side wall of the root chamber 103, reattach the black plastic film to the side wall of the root box 1, and put the root box 1 back into the water tank 2; then, install the transparent plastic film top cover 10 above the water tank 2 and seal it with waterproof tape.

[0093] (10) At 24 hours, remove the transparent plastic film top cover 10 and take out the two DGT probes 5 from the root chamber 103 and sediment chamber 104; at the same time, open the second test port 108 and the third test port 111 and take out the circular DGT 6. Put the root box 1 back into the water tank 2, and then install the transparent plastic film top cover 10 on top of the water tank 2 and seal it with waterproof tape. Then, elute with NaCl (1mol / L) and NaOH (1mol / L) solutions in sequence, and use a micro spectrophotometer and the aforementioned analytical methods to determine the concentrations of phosphorus, ammonia nitrogen and nitrate nitrogen in the eluent, and calculate the DGT concentration (μg / L) of the root surface and non-rhizosphere sediment pore water.

[0094] (11) At 48h, remove the transparent plastic film top cover 10, take out the two Peeper of root chamber 103 and sediment chamber 104, take out the pore water of each small chamber of Peeper, and immediately use a micro spectrophotometer and the aforementioned analytical methods to determine the concentration of phosphorus, ammonia nitrogen and nitrate nitrogen in the eluent to obtain the pore water concentration (μg / L) profile of root surface and non-rhizosphere sediments.

[0095] (12) After completing the above in-situ tests of root surface sediments and non-rhizosphere sediments, remove root box 1 from water tank 2 and immediately connect soil solution sampler 8 (Rhizon) to the first sampling port 109 (Rhizon sampling port) and the second sampling port 112 (Rhizon sampling port) to collect pore water of root surface sediments and non-rhizosphere sediments with a resolution of 1 cm. The pore water is immediately acidified and the concentrations of phosphorus, ammonia nitrogen and nitrate nitrogen in the pore water (μg / L) are determined using a micro spectrophotometer and the aforementioned analytical methods.

[0096] (13) First, remove the rear sidewall of root chamber 103, carefully remove a portion of the root surface deposits, and remove the roots of the two *Potamogeton crispus* plants along with the parts above the roots from root chamber 103. Bring the whole plant and deposits from root box 1 into the laboratory. Carefully separate the roots and deposits, wash the roots with water to minimize root loss; divide the plant into the root part and the part above the root. Then, dry the root part and the part above the root in an oven at 105°C for 1 hour, and then dry at 80°C for 72 hours until constant weight, and weigh its dry weight (root part and part above the root). Take 0.25g and digest the plant sample using the sulfuric acid-perchloric acid digestion method to obtain the digestion solution; then, determine the total phosphorus content using the ammonium molybdate spectrophotometric method; determine the total nitrogen using a KJeltec 2300 fully automatic nitrogen analyzer.

[0097] (14) Total phosphorus in sediments was determined using the SMT method. Phosphorus speciation in sediments was analyzed using the Hupfer method, classifying phosphorus into weakly adsorbed phosphorus (NH4Cl-P), reducible phosphorus (BD-P), aluminum / iron bound phosphorus (NaOH-srP), polyphosphate / organic phosphorus (NaOH-nrP), calcium bound phosphorus (HCl-P), and residual phosphorus (rest-P). Total nitrogen in sediments was determined using the semi-micro Kjeldahl method. Sediment nitrogen was subjected to continuous graded leaching experiments, classifying nitrogen into different bound forms, ion-exchangeable nitrogen, weakly acid-leached nitrogen, strongly alkali-leached nitrogen, and strongly oxidizing agent-leached nitrogen. When performing the above sediment and *Potamogeton crispus* tests, blank and standard substances for both plant and sediment samples should also be determined simultaneously (refer to GBW10023 and GBW07309), and the detection limits and recoveries should be provided. The recoveries of total nitrogen and total phosphorus in *Potamogeton crispus* were 91.21% and 106.5%, respectively; the recoveries of total nitrogen and total phosphorus in sediment were 94.55% and 108.5%, respectively.

[0098] Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this invention. Furthermore, those skilled in the art will recognize that, based on the ideas of this invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A root box system for in-situ testing of rhizosphere micro-regions of aquatic plants, characterized in that: Includes root box, in-situ testing device, water tank, aeration device and water tank circulation device; The in-situ testing device includes a DGT probe, a circular DGT, a detection membrane, a pore water sampler, and a soil solution sampler. The root chamber is equipped with a first filter screen at the bottom. Inside the root chamber, there is an upper overlying water layer and a root chamber and a sediment chamber located below the overlying water layer. The root chamber and the sediment chamber are separated by a second and a third filter screen arranged at intervals. The side wall of the root chamber is provided with a first test port, a second test port, and multiple first sampling ports. The first test port is provided with a detachable plate, and the inner side of the plate is used to attach the detection membrane. The side wall of the sediment chamber is provided with a third test port and multiple second sampling ports. The second and third test ports are respectively used to place the circular DGT into the root chamber and the sediment chamber or to remove the circular DGT from the root chamber and the sediment chamber. The first and second sampling ports are respectively used to connect to the soil solution sampler. The DGT probe and the pore water sampler are used to insert into the root chamber from above the root chamber. A lighting device is installed above the water tank to simulate sunlight. An aeration device is used to aerate the water tank. A water circulation device is connected to both ends of the water tank to form a circulation loop. A light-transmitting top cover is provided on the water tank to seal the opening at the top of the water tank. The root box is used to suspend in the water tank. An electrode probe is provided on the water tank to extend into the root box.

2. The root box system for in-situ testing of rhizosphere micro-regions of aquatic plants according to claim 1, characterized in that: The aeration device includes an aeration head, an air pump, and an air storage cylinder. One aeration head is installed at each end of the water tank. Each aeration head is connected to the main aeration pipe through an aeration branch pipe. The main aeration pipe is connected to the air pump. The air storage cylinder is connected to the main aeration pipe. A flow meter, a control valve, and a pressure reducing valve are also installed on the main aeration pipe between the air storage cylinder and the aeration branch pipe.

3. The root box system for in-situ testing of rhizosphere micro-regions of aquatic plants according to claim 1, characterized in that: The water tank circulation device includes a return water tank and a peristaltic pump. One end of the water tank is connected to the return water tank through a return pipe, and the other end is connected to the outlet end of the peristaltic pump through an inlet pipe. The return water tank is connected to the inlet end of the peristaltic pump through a pipeline.

4. The root box system for in-situ testing of rhizosphere micro-regions of aquatic plants according to claim 1, characterized in that: A crossbar is provided at the upper end of the water tank, the electrode probe is connected to the crossbar through an aluminum alloy ruler, and the root box is suspended on the crossbar by a cable.

5. The root box system for in-situ testing of rhizosphere micro-regions of aquatic plants according to claim 1, characterized in that: The detection membrane includes a fluorescent sensing membrane and a DGT adsorption membrane. The fluorescent sensing membrane is attached to the inner side of the plate, or both the fluorescent sensing membrane and the DGT adsorption membrane are attached simultaneously.

6. The root box system for in-situ testing of rhizosphere micro-regions of aquatic plants according to claim 1, characterized in that: The root box and the plate are both made of transparent plexiglass; the water tank is made of opaque plexiglass; the first filter, the second filter and the third filter are made of nylon with a pore size of 30μm.

7. The root box system for in-situ testing of rhizosphere micro-regions of aquatic plants according to claim 1, characterized in that: The light-transmitting top cover includes a top cover frame and a plastic film fixedly covering the top cover frame.

8. The root box system for in-situ testing of rhizosphere micro-regions of aquatic plants according to claim 2, characterized in that: The gas in the gas storage cylinder is argon or pure oxygen.

9. The root box system for in-situ testing of rhizosphere micro-regions of aquatic plants according to claim 1, characterized in that: Both ends of the second and third filter screens are fixed to the inner wall of the root box by plastic frames; each of the second and third test ports is provided with a sealing cap, which is used to seal the second and third test ports respectively; each of the first sampling ports and each of the second sampling ports is sealed with a rubber stopper.

10. A method for in-situ testing of rhizosphere micro-regions of aquatic plants, based on the root box system for in-situ testing of rhizosphere micro-regions of aquatic plants as described in any one of claims 1 to 9, characterized in that, Includes the following steps: (1) The sediments collected from the lake are dried, ground, sieved and mixed for pretreatment, and then lake water or tap water is added to make a paste. (2) Lake water or tap water is introduced into the water tank through the water tank water circulation device, and the water in the water tank is circulated back; According to the experimental requirements, reagents or pollutants are added to the water circulation device in the water tank, and the reagents or pollutants enter the water tank with the circulating water; (3) Fill the root box evenly with the paste-like sediment, cut the stem of the aquatic plant seedling and insert it into the center of the root chamber, and cover the side wall of the root box with black plastic film. (4) Suspend the root box in the water tank so that the root box is submerged below the water surface; insert the electrode probe into the root box and seal the upper opening of the water tank through the light-transmitting top cover; (5) By adjusting the lighting device, the aeration device and the water circulation device of the water tank, the water environment parameters in the water tank are controlled to make them close to the environmental conditions of the lake; the aquatic plants grow stably for three months. (6) In the later stage of aquatic plant growth, remove the root box, insert the DGT probe and the pore water sampler above the root chamber, and test the elemental profile of the root surface sediment in the root chamber; open the plate, attach the fluorescent sensing membrane or attach both the fluorescent sensing membrane and the DGT adsorption membrane, and then reinstall the plate; open the second test port and the third test port, place the circular DGT in the root surface sediment in the root chamber and the non-rhizosphere sediment in the sediment chamber respectively, and then close the second test port and the third test port; then place the root box back into the water tank. (7) At the 8th hour, take out the root box, remove the black plastic film from the side wall of the root box, place the root box in the planar optical electrode test device, and immediately take out the fluorescent sensing film or the fluorescent sensing film and the DGT adsorption film after completing the fluorescence analysis of the fluorescent sensing film in the root chamber for subsequent DGT fixative analysis; reinstall and reset the plate, reattach the black plastic film to the side wall of the root box, and put the root box back into the water tank to reset it; (8) At the 24th hour, the DGT probe and each of the circular DGTs were removed; (9) At the 48th hour, the pore water sampler was removed and subsequent root surface sediment pore water analysis was performed. (10) Connect the soil solution sampler to the first sampling port and the second sampling port, and take out the pore water sample from the root chamber and the sediment chamber; (11) Take out the root box, take out the root surface deposits and aquatic plants in the root chamber, take out the rhizosphere deposits between the second filter and the third filter, take out the non-rhizosphere deposits in the deposit chamber, mix the rhizosphere deposits and non-rhizosphere deposits separately and then carry out subsequent processing. (12) Separate the roots of aquatic plants from the sediment on the root surface, wash the roots clean, and separate the roots of aquatic plants from the parts above the roots for further processing. (13) The gel strip eluent of the DGT probe, the adsorption membrane eluent of the circular DGT, the pore water sample obtained by the pore water sampler, the pore water sample obtained by the soil solution sampler, the DGT adsorption membrane, the aquatic plant root and above-root sample, and the sediment sample are analyzed and tested, and the environmental parameter data of the fluorescent sensing membrane are analyzed. (14) Based on the analysis results and water environment parameters, study the geochemical reactions of rhizosphere elements, absorption-migration processes, and the influence mechanism of environmental parameters on rhizosphere processes of aquatic plants, and evaluate the water ecological restoration capacity of aquatic plants.

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