Submerged plant root system growth promoting substrate and application thereof

Abstract

The invention provides a submerged plant root system growth promoting substrate and application thereof. The submerged plant root system growth promoting substrate comprises the following components: composite pH response hydrogel; the preparation method of the composite pH response hydrogel comprises the following steps: 1) adding sodium alginate powder, nano montmorillonite, indoleacetic acid, gibberellic acid, calcium carbonate, methyl jasmonate and glycerol into a polyvinyl alcohol solution, stirring and performing ultrasonic treatment to obtain a uniform dispersion liquid; 2) freezing the uniform dispersion liquid to obtain a frozen body, and freeze-drying the frozen body in a freeze dryer to obtain a freeze-dried sample; 3) taking out the freeze-dried sample, and immersing the sample into a CaCl2 solution for crosslinking to obtain composite hydrogel; step 4) putting the composite hydrogel into a mixed solution of chitosan and starch, standing for a period of time, taking out, and immersing into a sodium hydroxide solution for cross-linking to obtain composite pH response hydrogel; the method is beneficial for the submerged plants to take root of bottom mud.

Description

Technical Field

[0001] The present invention relates to a submerged plant root growth promoting substrate and its application, belonging to the technical field of submerged plant cultivation. Background Art

[0002] The ecological restoration technology of submerged plants is a commonly used means for water ecological restoration. However, the cultivation of submerged plants faces problems such as low water transparency, hydraulic scouring, and poor bottom sediment conditions; the scouring of water flow can cause the seedlings of submerged plants to be difficult to take root, and even the phenomenon of "floating seedlings" occurs; moreover, the bottom sediments of some water bodies may be sandy, hardened, and silted, which is not conducive to the rooting and growth of submerged plant seedlings.

[0003] Currently, the commonly used method for sowing submerged plant seedlings is to throw the planting soil wrapped in non-woven fabric and the roots of the plants into the water; this method has many problems: it is impossible to accurately control the planting spacing and density, resulting in a low survival rate of the plants; when the plants sink to the bottom under the action of gravity and buoyancy, the depth of the rhizomes buried in the bottom sediment is insufficient, and it is easily affected by water flow disturbance, which easily leads to the phenomenon of floating seedlings. Summary of the Invention

[0004] The present invention provides a submerged plant root growth promoting substrate and its application, aiming to solve the problems that submerged plant seedlings are prone to floating seedlings and difficult to be planted in the bottom sediment in the water environment.

[0005] The technical solution of the present invention: A submerged plant root growth promoting substrate, the components of which include a composite pH-responsive hydrogel; the preparation method of the composite pH-responsive hydrogel includes:

[0006] Step 1) Add sodium alginate powder, nano-montmorillonite, indoleacetic acid, gibberellic acid, calcium carbonate, methyl jasmonate, and glycerol to a polyvinyl alcohol solution, stir and ultrasonically obtain a uniformly dispersed solution;

[0007] Step 2) Freeze the uniformly dispersed solution to obtain a frozen body, and then place the frozen body in a freeze dryer for freeze drying to obtain a freeze-dried sample;

[0008] Step 3) Take out the freeze-dried sample and immerse it in a CaCl2 solution for crosslinking to obtain a composite hydrogel;

[0009] Step 4) Place the composite hydrogel in a mixed solution of chitosan and starch, let it stand for a period of time, then take it out and immerse it in a sodium hydroxide solution for crosslinking to obtain a composite pH-responsive hydrogel.

[0010] Further, the mass ratio of the sodium alginate powder, nano-montmorillonite, indole acetic acid, gibberellic acid, calcium carbonate, methyl jasmonate, and glycerol is (1-3):(0.05-0.2):(0.05-0.2):(0.05-0.2):(0.2-0.7):(0.1-0.3):(0.1-0.3).

[0011] Further, 1 g - 3 g of sodium alginate powder is added to every 100 ml of polyvinyl alcohol solution.

[0012] Further, in step 1), the stirring and ultrasonic treatment to obtain a uniformly dispersed liquid is to stir for 8 hours - 11 hours, and then perform ultrasonic treatment for 15 minutes - 40 minutes to obtain a uniformly dispersed liquid.

[0013] Further, the sample after freeze-drying is taken out and immersed in a CaCl2 solution for crosslinking to obtain a composite hydrogel. Specifically: the sample after freeze-drying in the mold is taken out and immersed in a CaCl2 solution for crosslinking at 2°C - 6°C for 15 minutes - 40 minutes to obtain a composite hydrogel; the mass percentage of CaCl2 in the CaCl2 solution is 1 wt% - 4 wt%.

[0014] Further, the composite hydrogel is placed in a mixed solution of chitosan and starch, left standing for a period of time, then taken out and immersed in a sodium hydroxide solution for crosslinking to obtain a composite pH-responsive hydrogel. Specifically: the composite hydrogel is taken out and immersed in a mixed solution of chitosan and starch, left standing at room temperature for 10 minutes - 30 minutes, and then the composite hydrogel is taken out from the mixed solution of chitosan and starch and immersed in a sodium hydroxide solution for crosslinking at room temperature for 10 minutes - 30 minutes to obtain a composite pH-responsive hydrogel; the mass percentage of chitosan in the mixed solution of chitosan and starch is 0.5 wt% - 2 wt%, and the concentration of NaOH in the NaOH solution is 0.1 mol / L - 0.5 mol / L.

[0015] Further, the sample after freeze-drying obtained in step 2) is processed as follows and then immersed in a CaCl2 solution for crosslinking to obtain a composite hydrogel. Specifically, it includes: culturing the sample after freeze-drying and plant growth-promoting rhizobacteria in an LB liquid medium until the logarithmic growth phase OD600≈0.7 to form a cultured sample.

[0016] A method for promoting the growth of submersed plant roots using a submersed plant root growth-promoting substrate, the method comprising:

[0017] Step (1) laying the composite pH-responsive hydrogel on the surface of the bottom mud of the water area where submersed plant seedlings need to be planted;

[0018] Step (2) laying a submersed plant seed-hydrogel complex on the upper surface of the composite pH-responsive hydrogel;

[0019] Step (3) lays a sediment covering layer on the upper surface of the submerged plant seed-hydrogel complex.

[0020] Furthermore, the preparation method of the submerged plant seed-hydrogel complex includes:

[0021] Step 1-1): Add sodium alginate powder to pure water, stir and ultrasonically treat to obtain a uniformly dispersed solution;

[0022] Step 1-2): Mix the uniformly dispersed solution and the submerged plant seeds evenly and then pour them into a mold;

[0023] Step 1-3): Pour CaCl2 solution into the mold for crosslinking, and let it stand for a certain period of time to obtain the submerged plant seed-hydrogel complex.

[0024] Furthermore, in the step 1-1), the mass of the sodium alginate powder accounts for 1% to 3% of the mass of the pure water; in the step 1-1), stirring and ultrasonically treating to obtain a uniformly dispersed solution means stirring for 0.5 hour to 2 hours and then ultrasonically treating for 5 minutes to 15 minutes to obtain the uniformly dispersed solution; in the step 1-3), letting it stand for a certain period of time to obtain the submerged plant seed-hydrogel complex specifically means letting it stand for 20 minutes to 40 minutes to obtain the submerged plant seed-hydrogel complex; in the step 1-3), the mass percentage of CaCl2 in the CaCl2 solution is 1 wt% to 4 wt%.

[0025] Advantages of the present invention:

[0026] 1) The present invention can enable the submerged plant seedlings to grow smoothly at the bottom of the water, and prevent the phenomenon of "floating seedlings" during the growth process;

[0027] 2) The present invention can promote the growth of the roots of submerged plants and is beneficial to the submerged plants to take root in the sediment;

[0028] 3) The present invention is beneficial to the submerged plants to take root in the sediment with sandy, hard, or muddy textures;

[0029] 4) The present invention can provide growth nutrients for submerged plants and is beneficial to the growth of submerged plants;

[0030] 5) The present invention is convenient for further coupling with rhizosphere microbial remediation and provides a living place for rhizosphere microorganisms;

[0031] 6) The technological process of the present invention is extremely simple and convenient, the implementation cost is low, the maintenance and management are easy, and it is suitable for large-scale popularization and application. Description of the Drawings

[0032] Attached Figure 1 is a schematic diagram of the method for promoting the growth of the roots of submerged plants by using the substrate for promoting the growth of the roots of submerged plants prepared by the present invention.

[0033] Attached Figure 2 It is an SEM image of the cross-section of a composite hydrogel, with pores of 10 - 20 μm, having better mass transfer ability and being beneficial to the growth of plant roots.

[0034] Attached Figure 3 It shows the root conditions of submerged plants six months after planting, using pH-responsive hydrogel, composite hydrogel, composite pH-responsive hydrogel, and ck (hydrogel) as the hydrogel layers for promoting the growth of submerged plant roots under the same environmental conditions.

[0035] Attached Figure 4 It shows the dry weights of the roots of submerged plants six months after planting, using pH-responsive hydrogel, composite hydrogel, composite pH-responsive hydrogel, and ck (hydrogel) as the hydrogel layers for promoting the growth of submerged plant roots.

[0036] Attached Figure 5 It shows the lengths of the roots of submerged plants six months after planting, using pH-responsive hydrogel, composite hydrogel, composite pH-responsive hydrogel, and ck (hydrogel) as the hydrogel layers for promoting the growth of submerged plant roots. Detailed implementation method

[0037] A substrate for promoting the growth of submerged plant roots, the components of which include a composite pH-responsive hydrogel; the preparation method of the composite pH-responsive hydrogel includes:

[0038] Step 1) Add sodium alginate powder, nano-montmorillonite, indoleacetic acid, gibberellic acid, calcium carbonate, methyl jasmonate, and glycerol into a polyvinyl alcohol solution, stir and ultrasonicate to obtain a uniformly dispersed solution; preferably, the stirring and ultrasonication to obtain a uniformly dispersed solution is to stir for 8 hours to 11 hours and then ultrasonicate for 15 minutes to 40 minutes to obtain a uniformly dispersed solution; more preferably, the stirring and ultrasonication to obtain a uniformly dispersed solution is to stir at room temperature for 10 hours and then ultrasonicate for 30 minutes to obtain a uniformly dispersed solution;

[0039] Step 2) Pour the uniformly dispersed solution into a mold and place it at -190°C to -180°C for freezing to obtain a frozen body, and then place the frozen body in a freeze dryer for freeze drying to obtain a freeze-dried sample; the mold is preferably a metal mold, more preferably a copper mold; preferably, place the mold filled with the uniformly dispersed solution on the surface of liquid nitrogen for freezing;

[0040] Step 3) Take out the freeze-dried sample and immerse it in a CaCl2 solution for crosslinking to obtain a composite hydrogel; It can be seen from the attached Figure 2 that the composite hydrogel prepared in this step has pores of 10 μm to 20 μm, obviously having better mass transfer ability and being beneficial to the growth of plant roots;

[0041] Step 4) Place the composite hydrogel in a mixed solution of chitosan and starch, let it stand for a period of time, then take it out and immerse it in a sodium hydroxide (NaOH) solution for crosslinking to obtain a composite pH-responsive hydrogel; if step 2) is omitted during the preparation process of the above-mentioned composite pH-responsive hydrogel, what is obtained is a pH-responsive hydrogel.

[0042] In the raw materials for preparing the composite pH-responsive hydrogel, polyvinyl alcohol (PVA), sodium alginate, glycerol, and CaCl2 are hydrogel components, nano-montmorillonite, indole-3-acetic acid (IAA), gibberellic acid (GA3), calcium carbonate (CaCO3), and methyl jasmonate (MeJA) are growth inducer components, chitosan and starch are pH-responsive components, and NaOH is a crosslinking agent for chitosan and starch.

[0043] The mass ratio of the sodium alginate powder, nano-montmorillonite, indole-3-acetic acid, gibberellic acid, calcium carbonate, methyl jasmonate, and glycerol is (1 - 3):(0.05 - 0.2):(0.05 - 0.2):(0.05 - 0.2):(0.2 - 0.7):(0.1 - 0.3):(0.1 - 0.3), and more preferably 2:0.1:0.1:0.1:0.5:0.2:0.2; preferably 1 g - 3 g of sodium alginate powder is added to every 100 ml of the polyvinyl alcohol solution; the concentration of polyvinyl alcohol in the polyvinyl alcohol solution is preferably 7 g - 15 g of polyvinyl alcohol per 100 ml of water, and the concentration of polyvinyl alcohol in the polyvinyl alcohol solution is more preferably 10 g of polyvinyl alcohol per 100 ml of water.

[0044] Take out the freeze-dried sample and immerse it in a CaCl2 solution for crosslinking to obtain a composite hydrogel. Specifically: Take out the freeze-dried sample in the mold and immerse it in a CaCl2 solution for crosslinking at 2°C - 6°C for 15 minutes - 40 minutes to obtain a composite hydrogel. More preferably, take out the freeze-dried sample in the mold and immerse it in a CaCl2 solution for crosslinking at 4°C for 30 minutes to obtain a composite hydrogel; the mass percentage content of CaCl2 in the CaCl2 solution is preferably 1 wt% - 4 wt%, and the mass percentage content of CaCl2 in the CaCl2 solution is more preferably 2 wt%.

[0045] The composite hydrogel is placed in a mixed solution of chitosan and starch, left standing for a period of time, then taken out and immersed in a sodium hydroxide (NaOH) solution for crosslinking to obtain a composite pH-responsive hydrogel. Specifically: the composite hydrogel is taken out and immersed in the mixed solution of chitosan and starch, left standing at room temperature for 10 minutes to 30 minutes, more preferably 15 minutes, and then the composite hydrogel is taken out from the mixed solution of chitosan and starch and immersed in the sodium hydroxide solution for crosslinking at room temperature for 10 minutes to 30 minutes to obtain a composite pH-responsive hydrogel; the mass percentage of chitosan in the mixed solution of chitosan and starch is preferably 0.5 wt% to 2 wt%, the mass percentage of starch is preferably 0.5 wt% to 2 wt%, and the concentration of NaOH in the NaOH solution is preferably 0.1 mol / L to 0.5 mol / L.

[0046] Preferably, the freeze-dried sample obtained in step 2) is processed as follows and then step 3) is carried out. The freeze-dried sample is taken out and immersed in a CaCl2 solution for crosslinking to obtain a composite hydrogel, specifically including: the freeze-dried sample and plant growth-promoting rhizobacteria (PGPR) are cultured in an LB liquid medium until the logarithmic growth phase (OD600≈0.7) to form a cultured sample, then the cultured sample is taken out and immersed in a CaCl2 solution for crosslinking to obtain a microbial composite hydrogel, and then the microbial composite hydrogel is placed in a mixed solution of chitosan and starch, left standing for a period of time, taken out and immersed in a sodium hydroxide (NaOH) solution for crosslinking to obtain a microbial composite pH-responsive hydrogel; rhizosphere microorganisms are added, and the microorganisms have a growth-promoting effect on plants. The composite pH-responsive hydrogel has many pores, which is more conducive to loading microorganisms.

[0047] A method for promoting the growth of submerged plant roots using a submerged plant root growth-promoting substrate, the method comprising:

[0048] Step (1) laying the composite pH-responsive hydrogel on the surface of the bottom mud of the water area where submerged plant seedlings need to be planted; the laying thickness of the composite pH-responsive hydrogel is preferably 1 cm to 5 cm, and the laying thickness of the composite pH-responsive hydrogel is further preferably 2 cm;

[0049] Step (2) laying a submerged plant seed-hydrogel complex on the upper surface of the composite pH-responsive hydrogel; the laying thickness of the submerged plant seed-hydrogel complex is preferably 0.3 cm to 1.5 cm, and the laying thickness of the submerged plant seed-hydrogel complex is further preferably 0.7 cm;

[0050] Step (3) laying a sediment covering layer on the upper surface of the submerged plant seed-hydrogel complex; the thickness of the sediment covering layer is preferably 0.5 cm to 2 cm, and the thickness of the sediment covering layer is further preferably 1 cm.

[0051] The preparation method of the submersed plant seed-hydrogel complex is as follows:

[0052] Step 1-1): Add sodium alginate powder to pure water, stir and ultrasonicate to obtain a uniformly dispersed solution; the mass of the sodium alginate powder accounts for 1% to 3% of the mass of the pure water, and is further preferably 2%; the stirring and ultrasonication to obtain the uniformly dispersed solution is preferably stirring for 0.5 hour to 2 hours, and then ultrasonically treating for 5 minutes to 15 minutes to obtain the uniformly dispersed solution; the stirring and ultrasonication to obtain the uniformly dispersed solution is further preferably stirring at room temperature for 1 hour, and then ultrasonically treating for 10 minutes to obtain the uniformly dispersed solution;

[0053] Step 1-2): Mix the uniformly dispersed solution and the submersed plant seeds evenly and then pour them into a mold;

[0054] Step 1-3): Pour CaCl2 solution into the mold for crosslinking, and let it stand for a certain time to obtain the submersed plant seed-hydrogel complex; preferably, the submersed plant seed-hydrogel complex is obtained after standing for 20 minutes to 40 minutes, and further preferably, the submersed plant seed-hydrogel complex is obtained after standing for 30 minutes; the mass percentage of CaCl2 in the CaCl2 solution is preferably 1 wt% to 4 wt%, and the mass percentage of CaCl2 in the CaCl2 solution is further preferably 2 wt%.

[0055] Example 1

[0056] The preparation method of a composite pH-responsive hydrogel includes:

[0057] Step 1): Add sodium alginate powder, nano-montmorillonite, indoleacetic acid, gibberellic acid, calcium carbonate, methyl jasmonate, and glycerol to the polyvinyl alcohol solution, stir at room temperature for 10 hours, and then ultrasonically treat for 30 minutes to obtain a uniformly dispersed solution; the mass ratio of the sodium alginate powder, nano-montmorillonite, indoleacetic acid, gibberellic acid, calcium carbonate, methyl jasmonate, and glycerol is 2:0.1:0.1:0.1:0.5:0.2:0.2; 2 g of sodium alginate powder is added to every 100 ml of the polyvinyl alcohol solution; the concentration of polyvinyl alcohol in the polyvinyl alcohol solution is 10 g of polyvinyl alcohol in every 100 ml of water;

[0058] Step 2): Pour the uniformly dispersed solution into a mold and place it at -190°C to -180°C for freezing to obtain a frozen body, and then place the frozen body in a freeze dryer for freeze drying to obtain a freeze-dried sample; the mold is a copper mold;

[0059] Step 3) Take out the freeze-dried sample in the mold and immerse it in the CaCl2 solution for crosslinking at 4°C - 6°C for 30 minutes to obtain a composite hydrogel; the mass percentage of CaCl2 in the CaCl2 solution is 2wt%; from the attachment Figure 2 It can be seen that the composite hydrogel prepared in this step has pores with a size of 10μm - 20μm, and obviously has better mass transfer ability, which is beneficial to the growth of plant roots;

[0060] Step 4) Take out the composite hydrogel and immerse it in the chitosan and starch mixed solution for 20 minutes at room temperature, then take out the composite hydrogel from the chitosan and starch mixed solution and immerse it in the sodium hydroxide solution for crosslinking at room temperature for 20 minutes to obtain a composite pH-responsive hydrogel; the mass percentage of chitosan in the chitosan and starch mixed solution is 1wt%, the mass percentage of starch is 1wt%, and the concentration of NaOH in the NaOH solution is 0.3mol / L; if step 2) is omitted during the preparation process of the above composite pH-responsive hydrogel, what is obtained is a pH-responsive hydrogel.

[0061] As shown in the attachment Figure 3 and the attachment Figure 4 and the attachment Figure 5 Replace the composite hydrogel, pH-responsive hydrogel and hydrogel (ck) formed during the preparation of the composite pH-responsive hydrogel in Example 1 of the present invention with the composite pH-responsive hydrogel respectively, and use the method for promoting the growth of submerged plant roots given in Example 2 for comparison; from the attachment Figure 3 and the attachment Figure 4 and the attachment Figure 5 It can be seen that the promoting effects of the composite pH-responsive hydrogel, composite hydrogel and pH-responsive hydrogel on the quality of plant roots are significantly stronger than those of the hydrogel (ck); although the error of the plant root quality is relatively large, it can still be seen from the length of the plant roots that the promoting effect of the pH-responsive hydrogel on the growth of plant roots is stronger than that of the composite hydrogel on the growth of plant roots, and the composite pH-responsive hydrogel prepared by the present invention combines the excellent effects of the composite hydrogel and the pH-responsive hydrogel, further improving the promoting effect on the growth of plant roots, which is beneficial to the submerged plants to take root in the bottom mud of the corresponding water area.

[0062] For the pH-responsive hydrogel, gibberellic acid GA3 has the effect of inducing root elongation, and indoleacetic acid (IAA) and methyl jasmonate (MeJA) can stimulate the division of root tip cells and promote the expression of cell wall relaxation proteins, which is beneficial to root growth, and induce the reduction of organic acid secretion by roots and the increase of root pH, which leads to the swelling of the pH-responsive hydrogel, and then produces a slight squeezing effect on plant roots, promoting the growth of plant roots.

[0063] For the composite hydrogel, gibberellic acid GA3 has the effect of inducing root elongation. Indole acetic acid (IAA) and methyl jasmonate (MeJA) can stimulate root tip cell division and promote the expression of cell wall loosening proteins, which is beneficial to root growth. The composite hydrogel has pores with a size of 10 μm to 20 μm, which can better transport nutrients and growth-promoting substances to plant roots and promote growth.

[0064] Appendix Figure 3 , Appendix Figure 4 , Appendix Figure 5 The preparation method of the hydrogel (ck) in [appendix] is as follows:

[0065] Step 1) Add sodium alginate powder, nano-montmorillonite, indole acetic acid, gibberellic acid, calcium carbonate, methyl jasmonate, and glycerol into the polyvinyl alcohol solution, stir and ultrasonicate to obtain a homogeneous dispersion; the mass ratio of sodium alginate powder, nano-montmorillonite, indole acetic acid, gibberellic acid, calcium carbonate, methyl jasmonate, and glycerol is 2:0.1:0.1:0.1:0.5:0.2:0.2; add 2 g of sodium alginate powder into every 100 ml of polyvinyl alcohol solution; preferably, stir for 10 hours and then ultrasonicate for 30 minutes to obtain a homogeneous dispersion.

[0066] Step 2) Pour the homogeneous dispersion into the CaCl2 solution and crosslink at 4°C to 6°C for 30 minutes to obtain a hydrogel, and the mass percentage of CaCl2 in the CaCl2 solution is 2 wt%.

[0067] Example 2

[0068] A method for promoting the growth of submerged plant roots using a submerged plant root growth-promoting substrate, which includes:

[0069] Step (1) Lay the composite pH-responsive hydrogel on the surface of the bottom mud in the water area where submerged plant seedlings need to be planted; the laying thickness of the composite pH-responsive hydrogel is 2 cm.

[0070] Step (2) Lay the submerged plant seed-hydrogel complex on the upper surface of the composite pH-responsive hydrogel; the laying thickness of the submerged plant seed-hydrogel complex is 0.7 cm.

[0071] Step (3) Lay a sediment covering layer on the upper surface of the submerged plant seed-hydrogel complex; the thickness of the sediment covering layer is 1 cm.

[0072] The preparation method of the submerged plant seed-hydrogel complex is as follows:

[0073] Step 1-1) Add sodium alginate powder to pure water, stir and ultrasonicate to obtain a homogeneous dispersion; the mass of the sodium alginate powder accounts for 2% of the mass of the pure water; the specific operation of stirring and ultrasonication to obtain a homogeneous dispersion is to stir at room temperature for 1 hour and then ultrasonicate for 10 minutes to obtain a homogeneous dispersion;

[0074] Step 1-2) Mix the homogeneous dispersion and submerged plant seeds evenly and then pour them into a mold;

[0075] Step 1-3) Pour CaCl2 solution into the mold for crosslinking, and let it stand for 30 minutes to obtain a submerged plant seed-hydrogel complex; the mass percentage of CaCl2 in the CaCl2 solution is 2 wt%.

Claims

1. A submerged plant root growth promoting substrate, characterized in that Including composite pH-responsive hydrogel; The preparation method of the composite pH responsive hydrogel comprises: Step 1) adding sodium alginate powder, nano-montmorillonite, indoleacetic acid, gibberellic acid, calcium carbonate, methyl jasmonate and glycerol into a polyvinyl alcohol solution, stirring and ultrasonicating to obtain a uniform dispersion; Step 2) freezing the uniform dispersion to obtain a frozen body, and then placing the frozen body in a freeze dryer for freeze drying to obtain a freeze-dried sample; Step 3) taking out the freeze-dried sample and immersing it in a CaCl2 solution for cross-linking to obtain a composite hydrogel; Step 4) placing the composite hydrogel in a mixed solution of chitosan and starch and letting it stand for a period of time, then taking it out and immersing it in a sodium hydroxide solution for cross-linking to obtain a composite pH-responsive hydrogel.

2. The submerged plant root growth promoting substrate according to claim 1, characterized in that The mass ratio of the sodium alginate powder, nano-montmorillonite, indoleacetic acid, gibberellic acid, calcium carbonate, methyl jasmonate and glycerol is (1-3):(0.05-0.2):(0.05-0.2):(0.05-0.2):(0.2-0.7):(0.1-0.3):(0.1-0.3).

3. The submerged plant root growth promoting substrate according to claim 1, characterized in that Add 1g to 3g of sodium alginate powder to every 100ml of polyvinyl alcohol solution.

4. The submerged plant root growth promoting substrate according to claim 1, characterized in that In the step 1), the stirring and ultrasonic treatment to obtain a uniform dispersion is performed for 8 to 11 hours, followed by ultrasonic treatment for 15 to 40 minutes to obtain a uniform dispersion.

5. The submerged plant root growth promoting substrate according to claim 1, characterized in that The freeze-dried sample is taken out and immersed in a CaCl2 solution for cross-linking to obtain a composite hydrogel, specifically: the freeze-dried sample in the mold is taken out and immersed in a CaCl2 solution for cross-linking at 2°C to 6°C for 15 minutes to 40 minutes to obtain a composite hydrogel; the mass percentage of CaCl2 in the CaCl2 solution is 1wt% to 4wt%.

6. The submerged plant root growth promoting substrate according to claim 1, characterized in that The composite hydrogel is placed in a mixed solution of chitosan and starch and allowed to stand for a period of time, then taken out and immersed in a sodium hydroxide solution for cross-linking to obtain a composite pH responsive hydrogel. Specifically, the composite hydrogel is taken out and immersed in a mixed solution of chitosan and starch and allowed to stand at room temperature for 10 minutes to 30 minutes, and then the composite hydrogel is taken out from the mixed solution of chitosan and starch and immersed in a sodium hydroxide solution for cross-linking at room temperature for 10 minutes to 30 minutes to obtain the composite pH responsive hydrogel; the mass percentage of chitosan in the mixed solution of chitosan and starch is 0.5wt% to 2wt%, and the concentration of NaOH in the NaOH solution is 0.1mol / L to 0.5mol / L.

7. The submerged plant root growth promoting substrate according to claim 1, characterized in that Step 2) The freeze-dried sample is treated as follows and then immersed in a CaCl2 solution for cross-linking to obtain a composite hydrogel, specifically comprising: culturing the freeze-dried sample and the target plant rhizosphere growth-promoting bacteria in LB liquid culture medium until the logarithmic growth phase OD600≈0.7 to form a cultured sample.

8. A method for promoting the root growth of submerged plants using the submerged plant root growth promoting substrate according to any one of claims 1 to 7, characterized in that include: Step (1) laying the composite pH-responsive hydrogel on the bottom mud surface of the water area where submerged plant seedlings are to be planted; Step (2) laying a submerged plant seed-hydrogel complex on the upper surface of the composite pH-responsive hydrogel; Step (3) laying a sediment covering layer on the upper surface of the submerged plant seed-hydrogel complex.

9. The method for promoting the root growth of submerged plants using a submerged plant root growth promoting substrate according to claim 8, characterized in that The preparation method of the submerged plant seed-hydrogel complex comprises: Step 1-1) adding sodium alginate powder into pure water, stirring and ultrasonicating to obtain a uniform dispersion; Step 1-2) mixing the uniform dispersion and submerged plant seeds uniformly and pouring into a mold; Step 1-3) Pour CaCl2 solution into the mold for cross-linking, and after standing for a certain period of time, obtain a submerged plant seed-hydrogel complex.

10. The method for promoting the root growth of submerged plants using a submerged plant root growth promoting substrate according to claim 9, characterized in that In the step 1-1), the mass of sodium alginate powder accounts for 1% to 3% of the mass of pure water; in the step 1-1), stirring and ultrasonicating to obtain a uniform dispersion is stirring for 0.5 hour to 2 hours, and then ultrasonicating for 5 minutes to 15 minutes to obtain a uniform dispersion; in the step 1-3), the submerged plant seed-hydrogel complex is obtained after standing for a certain period of time, specifically, the submerged plant seed-hydrogel complex is obtained after standing for 20 minutes to 40 minutes; in the step 1-3), the mass percentage of CaCl2 in the CaCl2 solution is 1wt% to 4wt%.

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