Culture method for increasing duckweed thallus starch yield

Abstract

The invention relates to a culture method for improving duckweed thallus starch yield. The method comprises the following steps: adding a nutrient solution with the initial concentration of 40-50% into a culture device, inoculating duckweed according to 1-10% of the working volume, and dynamically adjusting the concentration of the nutrient solution according to the growth stage in the duckweed growth process: 1) in the rapid growth period, maintaining the concentration of the nutrient solution to be 40-50% of the original concentration, and at the moment, keeping the chlorophyll content of the duckweed to be 0.15-0.30 mg / g; and 2) starch accumulation period: gradually reducing the concentration of the nutrient solution to 30-40% of the original concentration, wherein the chlorophyll content of the duckweed is 0.10-0.20 mg / g. The corresponding distilled water is supplemented according to the evaporation volume of the nutrient solution for 2-3 times, the distilled water is supplemented every 1-2 days, the volume of the nutrient solution is kept stable during the period, and finally the duckweed thallus with the high starch yield is obtained. The method is short in culture period and low in cost; compared with conventional culture, the method has the advantages that the biomass and starch yield of the duckweed thallus can be synchronously improved, and a new thought is provided for the starch yield and subsequent comprehensive application of the duckweed thallus.

Description

Technical Field

[0001] The invention belongs to the technical field of duckweed biomass energy, in particular to a cultivation method for improving the starch yield of duckweed fronds. Background Art

[0002] Duckweed has become a starch resource with development potential due to its advantages such as fast growth rate, high nutrient utilization efficiency, and strong adaptability to various environments. Paradoxically, during the growth of duckweed, its nutrient utilization rate, i.e. biomass accumulation, is negatively correlated with starch accumulation (i.e. fast growth and low starch content; high starch content and relatively slow growth). In other words, it is difficult to achieve a balance between energy supply and whether it is mainly used for duckweed growth or starch accumulation. How to simultaneously increase duckweed's biomass and starch accumulation to achieve effective output of starch yield has always been a major problem in the duckweed cultivation process, and is also the key to the industrialization of duckweed starch.

[0003] At present, duckweed cultivation mainly involves several modes such as autotrophic, heterotrophic and co-cultivation. Generally speaking, under optimal growth conditions, the starch content of duckweed is maintained at a relatively low level, but under stress conditions such as nutrient limitation, salinity, strong light, plant hormone treatment, or after switching to a heterotrophic growth mode, the starch content of duckweed will increase. Nitrogen (N), phosphorus (P) and sulfur (S) are essential macronutrients for plant growth and development, and are involved in the formation of cell structure and high-energy molecules (nucleic acids, proteins, chlorophyll, adenosine triphosphate and phospholipids). Duckweed can survive and even reproduce in the absence of these macronutrients for a long time. At present, the two most studied starch induction methods are N limitation (NL) and P limitation (PL). However, these two strategies induce starch accumulation in duckweed at the expense of biomass production. Therefore, despite the high starch content, starch yield may be greatly affected due to the trade-off between starch induction and plant growth. So for a single element to be limited, there is no significant improvement in the final starch yield. While heterotrophic and combined cultivation methods can effectively increase biomass, the effect on starch yield is not obvious. In addition, since the carbon source used in the cultivation process is often glucose, the cost of the cultivation process increases, which is not suitable for subsequent industrial production. Therefore, it is particularly important to seek a low-cost and high-efficiency cultivation method.

[0004] Since duckweed has a rapid growth period and a starch accumulation period during its growth process, nutrient solution can be added accordingly according to the growth period to ensure that both biomass can be increased and starch can be accumulated in large quantities. Summary of the invention

[0005] The technical problems in the prior art such as being unable to balance the biomass and starch content of duckweed and achieving a good final starch yield are addressed. The present invention provides a cultivation method for increasing the starch yield of duckweed fronds, and the method is to dynamically regulate the concentration of the added nutrient solution. During the rapid growth period of duckweed, a higher concentration of nutrient solution can promote rapid growth of duckweed and accumulate sufficient biomass; after entering the starch accumulation period, reducing the concentration of the nutrient solution can induce duckweed to use more energy for starch synthesis, thereby achieving a better starch yield and realizing a double increase in biomass and starch accumulation. Since it is a complex system regulated by the nutrient solution, there is no restriction on sacrificing biomass of a certain element to achieve a high starch content, and there is no problem of high cost of adding exogenous carbon sources. The method is simple and easy to operate.

[0006] The present invention is achieved through the following technical solutions:

[0007] The first object of the present invention is to provide a method for increasing the starch yield of duckweed fronds, comprising the following steps:

[0008] (1) culturing the activated duckweed in a first nutrient solution under light;

[0009] (2) Rapid growth period: the duckweed obtained in step (1) is inoculated into a second nutrient solution for light culture; the second nutrient solution is obtained by diluting the first nutrient solution to a concentration of 40 to 50% by volume, during which the concentration is kept stable and the second nutrient solution is subsequently replenished;

[0010] (3) Starch accumulation period: the volume concentration of the second nutrient solution in step (2) is reduced to 30% to 40% of the concentration of the first nutrient solution, the light culture is continued, and distilled water is subsequently added.

[0011] In one embodiment of the present invention, in step (1), the duckweed is selected from one or more of the genera Spirodina multirhiza, Spirodina oligorhiza, Lemna, Lemna and Lemna spp.

[0012] In one embodiment of the present invention, in step (1), the first nutrient solution includes the following element components by weight percentage: calcium 0.2g / L~1g / L, iron 0.001g / L~0.0005g / L, magnesium 0.01g / L~0.05g / L, boron 0.0001g / L~0.0005g / L, zinc 0.00001g / L~0.00005g / L, copper 0.000004g / L~0.00002g / L, molybdenum 0.00001g / L~0.00005g / L, sodium 0.000004g / L~0.00002g / L, manganese 0.0002g / L~0.001g / L, nitrogen 0.06g / L~0.3g / L, phosphorus 0.006g / L~0.03g / L and potassium 0.12g / L~0.6g / L.

[0013] In one embodiment of the present invention, the first nutrient solution comprises the following components: Ca(NO 3 ) 2 ·4H 2 O 12g / L~60g / L, KNO 3 20 g / L~25 g / L, KH 2 PO 4 1 g / L~1.5g / L, tartaric acid 0.5g / L~1g / L, FeCl 3 6H 2 O1g / L~2g / L, EDTA 1.5g / L~2g / L, MgSO 4 7H 2 O 5g / L~10g / L, H 3 BO 3 0.5 g / L~1g / L, ZnSO 4 7H 2 O 0.05g / L~0.1g / L, Na 2 MoO 4 ·2H 2 O 0.02g / L~0.025g / L, CuSO 4 ·5H 2 O 0.015g / L~0.02g / L, MnCl 2 ·4H 2 O 0.5g / L~1g / L.

[0014] In one embodiment of the present invention, the pH value of the first nutrient solution is 5 to 5.5;

[0015] And / or, the pH value of the second nutrient solution is 5-5.5; the pH value of the second nutrient solution is obtained by regulation.

[0016] In one embodiment of the present invention, in step (2), the volume of duckweed accessed is 1% to 10% of the nutrient solution.

[0017] In one embodiment of the present invention, in step (2), the diluent used for dilution is distilled water.

[0018] In one embodiment of the present invention, in step (2), the light culture time is 1 to 3 days.

[0019] In one embodiment of the present invention, in step (3), the light culture time is 4 to 7 days.

[0020] In one embodiment of the present invention, the illumination intensity of the light culture is 85 μmol / m 2 / s~100μmol / m2 / s.

[0021] The second object of the present invention is to provide duckweed fronds obtained by the culture method, wherein the biomass of the duckweed fronds is ≥140.57±0.85 g / m 2 ; Starch yield ≥58.87±0.47g / m 2 .

[0022] The above technical solution of the present invention has the following advantages compared with the prior art:

[0023] (1) The culture method provided by the present invention has low cost, good effect and short cycle.

[0024] (2) Compared with conventional culture, the present invention can simultaneously increase the biomass and starch content of duckweed by changing the nutrient concentration according to the different growth stages of duckweed, that is, the biomass reaches 140.57±0.85g / m 2 Above, starch yield reaches 58.87±0.47g / m 2 above.

[0025] (3) The present invention provides a new idea for increasing the yield of duckweed starch and lays a foundation for developing duckweed starch resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below according to specific embodiments of the present invention in conjunction with the accompanying drawings, wherein:

[0027] Figure 1 It is a growth state diagram of duckweed cultivated in Examples 1 to 2 of the present invention and Comparative Examples 1 to 2;

[0028] Figure 2 The starch yield of duckweed cultured in Examples 1 and 2 of the present invention and Comparative Examples 1 and 2 at different stages is shown. DETAILED DESCRIPTION

[0029] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0030] The present invention provides a cultivation method for improving the starch yield of duckweed fronds, which is as follows:

[0031] Picking germplasm from the plate and adding it to a culture bottle containing the first nutrient solution, and irradiating it with light to obtain activated germplasm;

[0032] culturing the activated duckweed in the first nutrient solution under light;

[0033] A second nutrient solution is added to a culture device, wherein the volume concentration of the second nutrient solution is 40% to 50% of the first nutrient solution, and duckweed is added at 1 to 10% of the working volume. During the growth of the duckweed, the concentration of the nutrient solution is dynamically adjusted according to the growth stage: 1) during the rapid growth period (the first to third days), the concentration of the nutrient solution is maintained at 40% to 50% of the original concentration (the concentration of the first nutrient solution), at which time the duckweed chlorophyll content is 0.15 mg / g to 0.30 mg / g, and the evaporation volume is supplemented with a nutrient solution of a corresponding concentration; 2) during the starch accumulation period (the fourth to seventh days), the concentration of the nutrient solution is gradually reduced to 30% to 40% of the original concentration (the concentration of the first nutrient solution), at which time the duckweed chlorophyll content is 0.10 mg / g to 0.20 mg / g, and the evaporation volume of the nutrient solution is supplemented with corresponding distilled water, the supplementation frequency is 2 to 3 times, and distilled water is supplemented approximately every 1 to 2 days, during which the volume of the nutrient solution is kept stable, and finally a duckweed frond with a high starch yield is obtained.

[0034] The preparation method of the second nutrient solution is: at room temperature, the first nutrient solution is prepared according to normal duckweed expansion culture, and then the corresponding pure water is added in a volume ratio and mixed to obtain a nutrient solution with a concentration of 40% to 50%.

[0035] The components of the nutrient solution used in the present invention include: calcium, iron, magnesium, boron, zinc, copper, molybdenum, sodium, manganese, nitrogen, phosphorus, and potassium; in terms of weight percentage, the first nutrient solution includes the following elemental components: calcium 0.2g / L~1g / L, iron 0.001g / L~0.0005g / L, magnesium 0.01g / L~0.05g / L, boron 0.0001g / L~0.0005g / L, zinc 0.00001g / L~0 .00005g / L, copper 0.000004g / L~0.00002g / L, molybdenum 0.00001g / L~0.00005g / L, sodium 0.000004g / L~0.00002g / L, manganese 0.0002g / L~0.001g / L, nitrogen 0.06g / L~0.3g / L, phosphorus 0.006g / L~0.03g / L and potassium 0.12g / L~0.6g / L.

[0036] The culture conditions of the present invention are: the light-dark alternation condition is a photoperiod environment with 24h light intensity, and the light intensity is 85μmol / m 2 / s~100μmol / m 2 / s and cultured at room temperature.

[0037] The culture device of the present invention is a commercially available plastic basket of length*width*height (166mm×114mm×58mm), but is not limited to this model and can be enlarged or reduced in the same proportion.

[0038] The components of the nutrient solution used in the present invention are all from commercial sources, and may contain elements such as calcium, iron, magnesium, boron, zinc, copper, molybdenum, sodium, manganese, nitrogen, phosphorus, and potassium.

[0039] The duckweed used in the present invention is a dominant duckweed plant with a high starch content in the genus Lemna, including but not limited to Spirodendrum multirootum ZH0196.

[0040] Furthermore, the duckweed morphology is all duckweed fronds.

[0041] Furthermore, the duckweed species include but are not limited to the genus Spirodina multirhiza, Spirodina oligorhiza, Lemna nepalensis, Lemna gracilis, and Lemna sphaerocephala.

[0042] Furthermore, the lighting condition can be any fluorescent lamp that can achieve the lighting intensity.

[0043] The present invention also provides duckweed with high biomass and high starch content obtained by culturing the above method, which ultimately achieves high starch yield.

[0044] The duckweed fronds with high starch content of the present invention can be applied in the fields of biomass energy and agricultural biotechnology.

[0045] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods, and the materials, reagents, etc. used are all available from commercial sources unless otherwise specified.

[0046] The test method involved in the embodiments of the present invention is:

[0047] 1. Determination of duckweed biomass

[0048] Duckweeds at different stages were collected, transferred to filter bags, centrifuged for 5 min to remove free surface water, and then weighed using a balance. The samples were then treated in a freeze dryer for 48 h, and the dry weight was determined, which was then converted to biomass per unit area based on the culture area.

[0049] 2. Determination of starch content

[0050] The freeze-dried sample was crushed in a mortar and ground into granules. Take 0.1g of the sample and disperse it in 0.2mL of 80% ethanol, then add 2mL of 2M KOH and stir in an ice bath for 20min. Then add 8mL of 1.2M sodium acetate buffer (pH3.8), 0.1mL of α-amylase and amyloglucosidase, mix well and place in a 50℃ water bath for 30min. Transfer the sample to a fixed volume of 100mL, take the supernatant after centrifugation per unit volume for measurement. Use the Megazyme total starch detection kit for measurement.

[0051] 3. Determination of starch yield

[0052] The product of the measured starch content and biomass is the starch yield, which can be expressed as:

[0053] Starch yield (g / m 2 ) = biomass (g / m 2 )×starch content (%).

[0054] The composition of the nutrient solution involved in the embodiments of the present invention (g / L):

[0055] Ca(NO 3 ) 2 ·4H 2 O 12g, KNO 3 25 g, KH 2 PO 4 1.4 g, tartaric acid 0.6 g, FeCl 3 6H 2 O1g, EDTA1.8g, MgSO 4 7H 2 O 10g, H 3 BO 3 0.6 g, ZnSO 4 7H 2 O 0.044g, Na 2 MoO 4 ·2H 2 O 0.024g, CuSO 4 ·5H 2 O 0.016g, MnCl 2 ·4H 2 O 0.8g, pH 5~5.5.

[0056] Embodiment 1:

[0057] This embodiment provides a method for culturing duckweed fronds with high density and high starch yield, comprising the following steps:

[0058] (1) Activation of the multi-rooted Spirodendrum ZH0196 germplasm in a conical flask: Pick the germplasm from the plate and add it to a 250 mL culture bottle containing 150 mL of nutrient solution. Irradiate with light for 24 h for 15 days to obtain the activated germplasm.

[0059] (2) The activated germplasm was inoculated at 80% into a culture device containing nutrient solution and cultured under 24-hour illumination for 4 days.

[0060] (3) Add 45% nutrient solution with an initial pH of 5 to 5.5 to the culture device, and inoculate the expanded duckweed into the culture device at 5% of the working volume. Maintain the nutrient concentration at 45% for the first three days. As the duckweed grows, the nutrient concentration is gradually reduced to 35% from the fourth day. The reduced amount of nutrient solution is supplemented with distilled water to maintain the volume of the culture solution. The solution is supplemented once every 1 to 2 days for a total of three times. The whole process is cultured under full illumination at a temperature of 25°C. After growing to 5 days, high-density duckweed with high starch content can be obtained after harvest.

[0061] Embodiment 2:

[0062] This embodiment provides a method for culturing duckweed fronds with high density and high starch yield, comprising the following steps:

[0063] (1) Activation of the multi-rooted Spirodendrum ZH0196 germplasm in a conical flask: Pick the germplasm from the plate and add it to a 250 mL culture bottle containing 150 mL of nutrient solution. Irradiate with light for 24 h for 15 days to obtain the activated germplasm.

[0064] (2) The activated germplasm was inoculated at 80% into a culture device containing nutrient solution and cultured under 24-hour illumination for 4 days.

[0065] (3) Add 50% nutrient solution with an initial pH of 5 to 5.5 to the culture device, and inoculate the expanded duckweed into the culture device at 5% of the working volume. Maintain the nutrient solution concentration at 50% for the first three days. As the duckweed grows, the nutrient solution concentration is gradually reduced to 40% from the fourth day. The reduced amount of nutrient solution is supplemented with distilled water to maintain the volume of the culture solution. The solution is supplemented once every 1 to 2 days for a total of three times. The whole process is cultured under full illumination at a temperature of 25°C. After growing to 5 days, high-density duckweed with high starch content can be obtained after harvest.

[0066] Comparative Example 1:

[0067] This comparative example provides a method for culturing duckweed fronds with high density and high starch yield, comprising the following steps:

[0068] (1) Activation of the multi-rooted Spirodendrum ZH0196 germplasm in a conical flask: Pick the germplasm from the plate and add it to a 250 mL culture bottle containing 150 mL of nutrient solution. Irradiate with light for 24 h for 15 days to obtain the activated germplasm.

[0069] (2) The activated germplasm was inoculated at 80% into a culture device containing nutrient solution and cultured under 24-hour illumination for 4 days.

[0070] (3) A 20% concentration of nutrient solution with an initial pH of 5 to 5.5 is added to the culture device, and the expanded duckweed is inoculated into the culture device at 5% of the working volume. As the duckweed grows, the amount of nutrient solution decreases and is later supplemented with distilled water to maintain the volume of the initial culture solution. The solution is supplemented once every 1 to 2 days for a total of 3 times. The whole process is cultured under full illumination at a temperature of 25°C. After the duckweed grows to 4 days, high-density duckweed with a high starch content can be obtained after harvest.

[0071] Comparative Example 2:

[0072] This comparative example provides a method for culturing duckweed fronds with high density and high starch yield, comprising the following steps:

[0073] (1) Activation of the multi-rooted Spirodendrum ZH0196 germplasm in a conical flask: Pick the germplasm from the plate and add it to a 250 mL culture bottle containing 150 mL of nutrient solution. Irradiate with light for 24 h for 15 days to obtain the activated germplasm.

[0074] (2) The activated germplasm was inoculated at 80% into a culture device containing nutrient solution and cultured under 24-hour illumination for 4 days.

[0075] (3) A 60% concentration of nutrient solution with an initial pH of 5 to 5.5 is added to the culture device, and the expanded duckweed is inoculated into the culture device at 5% of the working volume. As the duckweed grows, the amount of nutrient solution decreases and is later supplemented with distilled water to maintain the volume of the initial culture solution. The solution is supplemented once every 1 to 2 days for a total of 3 times. The whole process is cultured under full illumination at a temperature of 25°C. After the duckweed grows to 6 days, high-density duckweed with a high starch content can be obtained after harvest.

[0076] Comparative Example 3:

[0077] This comparative example provides a method for culturing duckweed fronds with high density and high starch yield, comprising the following steps:

[0078] (1) Activation of the multi-rooted Spirodendrum ZH0196 germplasm in a conical flask: Pick the germplasm from the plate and add it to a 250 mL culture bottle containing 150 mL of nutrient solution. Irradiate with light for 24 h for 15 days to obtain the activated germplasm.

[0079] (2) The activated germplasm was inoculated at 80% into a culture device containing nutrient solution and cultured under 24-hour illumination for 4 days.

[0080] (3) A 40% concentration of nutrient solution with an initial pH of 5 to 5.5 is added to the culture device, and the expanded duckweed is inoculated into the culture device at 5% of the working volume. As the duckweed grows, the amount of nutrient solution decreases and is later supplemented with distilled water to maintain the volume of the initial culture solution. The solution is supplemented every 1 to 2 days for a total of 3 times. The whole process is cultured under full illumination at a temperature of 25°C. After the duckweed grows to 5 days, high-density duckweed with a high starch content can be obtained after harvest.

[0081] Comparative Example 4:

[0082] This comparative example provides a method for culturing duckweed fronds with high density and high starch yield, comprising the following steps:

[0083] (1) Activation of the multi-rooted Spirodendrum ZH0196 germplasm in a conical flask: Pick the germplasm from the plate and add it to a 250 mL culture bottle containing 150 mL of nutrient solution. Irradiate with light for 24 h for 15 days to obtain the activated germplasm.

[0084] (2) The activated germplasm was inoculated at 80% into a culture device containing nutrient solution and cultured under 24-hour illumination for 4 days.

[0085] (3) A 50% concentration of nutrient solution with an initial pH of 5 to 5.5 is added to the culture device, and the expanded duckweed is inoculated into the culture device at 5% of the working volume. As the duckweed grows, the amount of nutrient solution decreases and is later supplemented with distilled water to maintain the volume of the initial culture solution. The solution is supplemented once every 1 to 2 days for a total of 3 times. The whole process is cultured under full illumination at a temperature of 25°C. After the duckweed grows to 5 days, high-density duckweed with a high starch content can be obtained after harvest.

[0086] The growth status of duckweed cultivated in Examples 1 to 2 of the present invention and Comparative Examples 1 to 2 is shown in the figure below: Figure 1 shown; through Figure 1 It can be seen that the higher the nutrient concentration, the more it is used for the growth of thallus and the less starch is accumulated.

[0087] The starch yields of duckweed cultured in Examples 1 to 2 of the present invention and Comparative Examples 1 to 2 at different stages are shown in FIG. Figure 2 shown by Figure 2 It can be seen that cultivation at different nutrient concentrations will result in different thallus growth cycles.

[0088] Table 1 shows the optimal biomass, starch content and yield of duckweed fronds cultured in Examples 1-2 and Comparative Examples 1-2, as follows:

[0089] Table 1

[0090] <![CDATA[Biomass / gm 2 > Starch content% <![CDATA[Starch yield / gm 2 > Example 1 145.68±0.53 42.60±0.46 61.77±0.44 Example 2 140.57±0.85 41.88±0.53 58.87±0.47 Comparative Example 1 127.98±4.80 42.06±0.76 53.80±1.06 Comparative Example 2 171.05±3.60 31.13±0.22 53.24±0.74 Comparative Example 3 131.44±0.93 37.82±0.33 49.71±0.56 Comparative Example 4 138.21±1.08 35.11±0.28 48.37±0.77

[0091] As can be seen from Table 1, according to the different growth stages of duckweed, the method of changing the nutrient concentration made the duckweed biomass reach a maximum of 145.68±0.53g / m 2 The highest starch yield reached 61.77±0.44g / m 2 , much higher than the comparative example using a single nutrient solution concentration. This is mainly because the duckweed in Examples 1 and 2 requires a higher nutrient solution concentration in the early growth stage to support rapid cell division and growth. At this time, sufficient nutrition can promote the development of duckweed's leaves and roots, laying a good foundation for subsequent growth; while in the later growth stage, the growth rate of duckweed gradually slows down, but the accumulation of starch continues. At this time, appropriately reducing the nutrient solution concentration can avoid excessive nutrient supply leading to plant leggy growth, while maintaining a certain nutrient level to maintain starch synthesis and accumulation, and ultimately increase starch yield. Comparative Examples 1 and 3 can clearly see that when the nutrient concentration is high, it is mainly used for biomass accumulation, and the degree of starch accumulation is not high; Comparative Examples 3 and 4 use a single nutrient concentration to cultivate with the growth of duckweed, and the later nutrients can no longer supply the growth of duckweed. Although starch is accumulating, the starch yield at this time is not as good as that of Examples 1 and 2.

[0092] Obviously, the above embodiments are merely examples for clear explanation and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the protection scope of the invention.

Claims

1. A method for increasing starch yield in duckweed fronds, characterized in that: The following steps are involved: (1) culturing the activated duckweed in a first nutrient solution under light; (2) Rapid growth period: the duckweed obtained in step (1) is inoculated into a second nutrient solution for light culture; the second nutrient solution is obtained by diluting the first nutrient solution to a concentration of 40 to 50% by volume, during which the concentration is kept stable and the second nutrient solution is subsequently replenished; (3) Starch accumulation period: the volume concentration of the second nutrient solution in step (2) is reduced to 30% to 40% of the concentration of the first nutrient solution, the light culture is continued, and distilled water is subsequently added.

2. The culture method according to claim 1, characterized in that In step (1), the duckweed is selected from one or more of the genera Spirodina multirhiza, Spirodina oligorhiza, Lemna spp., Lemna spp. and Lemna spp.

3. The culture method according to claim 1, characterized in that In step (1), the first nutrient solution includes the following element components by weight percentage: calcium 0.2g / L~1g / L, iron 0.001g / L~0.0005g / L, magnesium 0.01g / L~0.05g / L, boron 0.0001g / L~0.0005g / L, zinc 0.00001g / L~0.00005g / L, copper 0.0000 04g / L~0.00002g / L, molybdenum 0.00001g / L~0.00005g / L, sodium 0.000004g / L~0.00002g / L, manganese 0.0002g / L~0.001g / L, nitrogen 0.06g / L~0.3g / L, phosphorus 0.006g / L~0.03g / L and potassium 0.12g / L~0.6g / L.

4. The culture method according to claim 3, characterized in that The first nutrient solution comprises the following components: Ca(NO3)2·4H2O 12g / L~60g / L, KNO3 20 g / L~25g / L, KH2PO4 1g / L~1.5g / L, tartaric acid 0.5g / L~1g / L, FeCl3·6H2O 1g / L~2g / L, EDTA 1.5g / L~2g / L, MgSO4·7H2O 5g / L~10g / L, H3BO3 0.5g / L~1g / L, ZnSO4·7H2O 0.05g / L~0.1g / L, Na2MoO4·2H2O 0.02g / L~0.025g / L, CuSO4·5H2O 0.015g / L~0.02g / L, MnCl2·4H2O 0.5g / L~1g / L.

5. The culture method according to claim 1, characterized in that The pH value of the first nutrient solution is 5 to 5.5; And / or, the pH value of the second nutrient solution is 5-5.

5.

6. The culture method according to claim 1, characterized in that In step (2), the volume of duckweed accessed is 1% to 10% of the nutrient solution.

7. The culture method according to claim 1, characterized in that: In step (2), the light culture time is 1 to 3 days.

8. The culture method according to claim 1, characterized in that: In step (3), the light culture time is 4 to 7 days.

9. The culture method according to claim 1, characterized in that: In step (2) and step (3), the illumination intensity of the illumination culture is 85 μmol / m 2 / s~100μmol / m 2 / s.

10. The duckweed frond obtained by the cultivation method according to any one of claims 1 to 9, characterized in that: The biomass of duckweed fronds is ≥140.57±0.85 g / m 2 ; Starch yield ≥58.87±0.47g / m 2 .

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