Method for evaluating cadmium transport capacity of reed based on plant functional traits

Abstract

This invention belongs to the field of soil remediation technology and relates to a method for assessing the cadmium translocation capacity of reeds based on plant functional traits. The method involves measuring the basal diameter, stomatal conductance, and transpiration rate of normally growing reeds. A cadmium translocation assessment index, R = (R1 + R2 + R3) / 3, is calculated based on these parameters, where R1, R2, and R3 are the transpiration rate assessment index, stomatal conductance assessment index, and basal diameter assessment index, respectively. This cadmium translocation assessment index is then used to evaluate the cadmium translocation capacity of the reeds. This method allows for the assessment of cadmium translocation capacity of reeds without cadmium treatment, simply by measuring some functional traits, thus reducing cadmium pollution and ensuring safety and environmental protection. It also helps in screening reed strains with high cadmium translocation capacity, improving the application efficiency of reeds in heavy metal pollution remediation.

Description

Technical Field

[0001] This invention belongs to the field of soil remediation technology and relates to a method for evaluating the cadmium translocation capacity of reeds based on plant functional traits. Background Technology

[0002] Heavy metal pollution is becoming increasingly serious, posing a significant environmental problem in my country and globally. Cadmium pollution is the most severe, and ecological restoration of cadmium-contaminated soils in my country is a pressing challenge. According to the "National Soil Pollution Status Survey Bulletin" published in 2014 by the former Ministry of Environmental Protection and the Ministry of Land and Resources, cadmium ranked first among the 11 pollutants surveyed, with an exceedance rate of 7.0%. In the "Soil Pollution Prevention and Control Action Plan" issued by the State Council in 2016, cadmium was also a key heavy metal monitored. In the 2018 National Soil Environmental Standard (GB15618-2018) survey of 11 pollutants, cadmium also ranked first in the exceedance rate of risk screening values ​​for agricultural land soil pollution. The detailed investigation results of soil pollution in the "2021 China Ecological Environment Status Bulletin" released by the Ministry of Ecology and Environment in 2021 showed that heavy metals are the main pollutants affecting the environmental quality of agricultural land soil, with cadmium being the primary pollutant. Phytoremediation, a new technology developed in recent years for treating heavy metal-contaminated soil, is based on the absorption and accumulation of heavy metals in polluted environments by specific plants. It has attracted much attention due to its environmental friendliness, green and low-carbon advantages.

[0003] Currently, there are several methods for remediating cadmium-contaminated soil using specific plants. For example, Chinese patent document CN202111314353.5 discloses an optimized remediation method for moderately cadmium-contaminated soil containing *Solanum nigrum*. This method promotes the growth of *Solanum nigrum* by applying additional fertilizer during its bud stage, thereby increasing its ability to accumulate cadmium in the soil. The entire plant is then harvested at maturity to remediate the moderately cadmium-contaminated soil. Chinese patent document CN202010347575.6 discloses an enhanced remediation method using hyperaccumulating plants to remediate cadmium-contaminated soil. This method uses *Tagetes patula* seedlings as hyperaccumulating plants and salicylic acid solution as an enhancer, which significantly strengthens the cadmium remediation capacity of the *Tagetes patula* seedlings. Among the various plant-based methods for remediating cadmium-contaminated soil disclosed so far, the application of reeds is relatively rare.

[0004] Reed (Phragmites australis), a typical wetland plant, is characterized by its well-developed root system, rich variety, and strong adaptability. It can transport cadmium to its above-ground parts, allowing for the removal of cadmium pollution from the soil through harvesting. However, current applications of reed in cadmium pollution remediation primarily focus on biochar preparation. For example, Chinese patent document CN202010300321.9 discloses a reed stalk biochar composite material, using rhamnolipid-modified reed stalk biochar composite material for remediating soil contaminated with the heavy metal cadmium. Chinese patent document CN201910622757.7 discloses a method for preparing multi-site activated and modified reed-reed biochar for the removal of heavy metals zinc and cadmium from water and soil. However, methods for directly applying reed plants to cadmium pollution remediation are lacking.

[0005] Generally, a common method is to apply cadmium treatment to the plant and then calculate its translocation coefficient. For example, Chinese patent document CN201811003842.7 discloses a method for improving the cadmium enrichment and translocation coefficient of ramie, finding that ramie harvested for fiber processing at the fiber maturity stage has higher enrichment and translocation capabilities. However, a method is lacking for assessing the plant's cadmium translocation capacity without applying cadmium treatment.

[0006] Therefore, developing a method for screening high-transporting reeds based on functional traits can not only quickly and efficiently select reed strains with strong translocation capabilities, but also compare the cadmium translocation capacity of reeds based solely on the determination of functional traits without applying cadmium treatment. This reduces pollution and research costs, and is of great significance for heavy metal phytoremediation projects. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a method for rapidly assessing the cadmium translocation capacity of reeds based solely on functional traits without the need for cadmium treatment. This method helps in selecting reed strains with strong cadmium translocation capabilities. The selected reeds have a stronger ability to translocate cadmium from the underground part to the above-ground part, thus allowing cadmium pollution in the soil to be removed by harvesting the above-ground part of the reeds.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: a method for evaluating the cadmium translocation capacity of reeds based on plant functional traits, the method comprising: measuring the basal diameter, stomatal conductance, and transpiration rate of normally growing reeds; calculating the cadmium translocation evaluation index R = (R1 + R2 + R3) / 3 based on the basal diameter, stomatal conductance, and transpiration rate, wherein R1, R2, and R3 are the transpiration rate evaluation index, stomatal conductance evaluation index, and basal diameter evaluation index, respectively; and evaluating the cadmium translocation capacity of reeds using the cadmium translocation evaluation index.

[0009] Preferably, the functional traits are measured when the reeds have grown to maturity, at which time the reed height is between 104-112 cm.

[0010] Preferably, the stomatal conductance and transpiration rate of reeds are measured between 8:00 AM and 12:00 PM, selecting the 1st to 3rd leaves from the upper part of the reed, with a leaf width between 0.9 and 1.2 cm, using a Li-cor 6800 photosynthesis meter.

[0011] Preferably, the basal diameter of the reed is the diameter of the stem at the bottom of the plant, measured with vernier calipers at a distance of 2-5 cm from the soil.

[0012] Preferably, based on the measured transpiration rate, the average transpiration rate of each reed genotype and the maximum transpiration rate among all reeds are calculated, and the average transpiration rate of each reed genotype is divided by the maximum transpiration rate among all reeds to obtain the transpiration rate assessment index for that genotype.

[0013] Preferably, the average stomatal conductance of each genotype of reed and the maximum stomatal conductance of all reeds are calculated based on the measured stomatal conductance. The stomatal conductance assessment index of that genotype is obtained by dividing the average stomatal conductance of each genotype of reed by the maximum stomatal conductance of all reeds.

[0014] Preferably, based on the measured basal diameter of the reeds, the average basal diameter of each genotype of reed and the maximum basal diameter among all reeds are calculated, and the average basal diameter of each genotype of reed is divided by the maximum basal diameter among all reeds to obtain the basal diameter assessment index of that genotype.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] (1) A method for evaluating the cadmium transport capacity of reeds is provided; the method is simple to operate and has high accuracy.

[0017] (2) The method of the present invention can assess the cadmium transport capacity of reeds by measuring some functional traits of reeds without applying cadmium treatment, thereby reducing cadmium pollution and being safe and environmentally friendly.

[0018] (3) It helps to screen reed varieties with high cadmium translocation capacity, which can improve the application efficiency of reeds in heavy metal pollution remediation. Attached Figure Description

[0019] Appendix Figure 1 The cadmium transport assessment index for each genotype of reed is calculated using the method of this invention;

[0020] Appendix Figure 2 The cadmium translocation coefficients for each genotype of reed are obtained using the cadmium treatment method.

[0021] Appendix Figure 3 Correlation analysis was conducted between cadmium translocation coefficients and cadmium translocation assessment indices for different genotypes of reed. Detailed Implementation

[0022] To facilitate understanding of this research, a more detailed description is provided below with reference to the accompanying drawings and specific embodiments. However, this research can be implemented in many different forms and is not limited to the embodiments described in this specification. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the disclosure of this research.

[0023] Example 1: This invention provides a method for evaluating the cadmium transport capacity of reeds based on plant functional traits. The method includes:

[0024] (1) Measure the basal diameter, stomatal conductance, and transpiration rate of normally growing reeds.

[0025] Stomatal conductance and transpiration rate of reeds were measured between 8:00 AM and 12:00 PM, selecting the top 1-3 leaves of the reeds. Leaf width ranged from 0.9 to 1.2 cm, and measurements were taken using a Li-cor 6800 (LI-6800, LI-COR Biosciences, USA) photosynthesis system. Functional traits were measured when the reeds reached maturity, at which point the plant height was between 104 and 112 cm.

[0026] (2) Calculate the cadmium transport assessment index

[0027] Based on the measured transpiration rates, the average transpiration rate of each reed genotype and the maximum transpiration rate among all reeds are calculated. The transpiration rate assessment index R1 for that genotype is obtained by dividing the average transpiration rate of each reed genotype by the maximum transpiration rate among all reeds.

[0028] The stomatal conductance of each genotype of reed is calculated based on the measured stomatal conductance, and the maximum stomatal conductance of all reeds is calculated. The stomatal conductance assessment index R2 of that genotype is obtained by dividing the average stomatal conductance of each genotype of reed by the maximum stomatal conductance of all reeds.

[0029] Based on the measured basal diameter of the reeds, the average basal diameter of each genotype and the maximum basal diameter of all reeds are calculated. The basal diameter assessment index R3 of that genotype is obtained by dividing the average basal diameter of each genotype by the maximum basal diameter of all reeds.

[0030] The cadmium transport assessment index R = (R1 + R2 + R3) / 3.

[0031] (3) The cadmium translocation assessment index was used to assess the cadmium translocation capacity of reeds.

[0032] Comparing the cadmium translocation assessment index of each reed genotype, reeds with a higher cadmium translocation assessment index have a stronger ability to translocate cadmium.

[0033] Example 2: This invention uses correlation analysis between functional traits of reeds and cadmium translocation coefficients to identify traits significantly correlated with cadmium translocation capacity. The top three significantly correlated functional traits are selected, and a cadmium translocation assessment index is calculated. Therefore, the cadmium translocation assessment index can be calculated based on functional traits, thereby screening reed strains with strong translocation capacity. The selected reeds are more suitable for removing cadmium pollution from the soil through harvesting. Specific implementation steps are as follows:

[0034] (1) Four genotypes of reeds from lineage O and lineage P were selected as experimental materials. The eight genotypes of reeds (CX01, NX25, G2, CN2024, SD01, SD05, CN2028, JS02) were from Heze, Shandong; Zhongwei, Ningxia; Panjin, Liaoning; Dongying, Shandong; Weifang, Shandong; Dongying, Shandong; Panjin, Liaoning; and Nanjing, Jiangsu, with four replicates for each genotype.

[0035] Table 1 List of Experimental Samples

[0036]

[0037]

[0038] (2) The cultivation method for reeds is rhizome cultivation. Rhizomes of reeds are dug up from a homogeneous garden and hydroponically cultured for one week to allow them to sprout. Large rhizomes are then cut into smaller pieces, each with two sprouted buds, approximately 4-6 cm in size and uniform in growth. After one week, the rhizomes are transplanted into flowerpots for further cultivation. Each flowerpot contains one small rhizome piece, with a top diameter of 16 cm, a bottom diameter of 13 cm, and a height of 17.5 cm. The culture medium is a mixture of vermiculite and nutrient soil, with a vermiculite to nutrient soil ratio of 2:1. The fresh weight of the soil in each pot is approximately 1.25 kg, and the dry weight is approximately 0.35 kg. Regular watering, weeding, and pest control are performed on the reeds.

[0039] (3) The experiment included a control group and a cadmium treatment group, with a cadmium treatment concentration of 20 mg·kg⁻¹. -1 After two months of cultivation, the cadmium-treated group was treated. The reed plants were treated with CdCl2 solution. 1.61g of CdCl2 was weighed into a 300mL beaker, dissolved in a small amount of water, transferred to a 1000mL volumetric flask, diluted to the mark with water, and shaken well. At this point, 1mL of the solution contained 1mg of cadmium. 7mL of this solution was added to each pot in the cadmium-treated group. The control group received no treatment and grew naturally.

[0040] (4) After cadmium treatment, the reeds grew to maturity, and the functional traits of the control group reeds and the cadmium content of the cadmium-treated group reeds were measured.

[0041] (5) The basal diameter of the reed is the diameter of the stem at the bottom of the plant, 2-5 cm from the soil, measured using vernier calipers; the stomatal conductance and transpiration rate of the reed were measured between 8:00 AM and 12:00 PM, selecting the 1st to 3rd leaves from the upper part of the reed, with leaf width between 0.9-1.2 cm, using a Li-cor 6800 photosynthesis system (LI-6800, LI-COR Biosciences, USA). The measurement data are shown in Table 2.

[0042] Table 2 Sample Measurement Data

[0043]

[0044]

[0045] (6) Calculation of the cadmium translocation assessment index. The cadmium translocation assessment index was calculated using an Excel spreadsheet. The average transpiration rate of each genotype of reed and the maximum transpiration rate among all reeds were calculated. The average transpiration rate of each genotype of reed was divided by the maximum transpiration rate among all reeds to obtain the transpiration rate assessment index R1 for that genotype. The average stomatal conductance of each genotype of reed and the maximum stomatal conductance among all reeds were calculated. The average stomatal conductance of each genotype of reed was divided by the maximum stomatal conductance among all reeds to obtain the stomatal conductance assessment index R2 for that genotype. The average basal diameter of each genotype of reed and the maximum basal diameter among all reeds were calculated. The average basal diameter of each genotype of reed was divided by the maximum basal diameter among all reeds to obtain the basal diameter assessment index R3 for that genotype. The cadmium translocation assessment index = (R1 + R2 + R3) / 3.

[0046] (7) Compare the cadmium translocation assessment index for each genotype of reed. Reeds with a higher cadmium translocation assessment index have a stronger ability to translocate cadmium. The cadmium translocation assessment indices for the eight genotypes of reed are as follows: Figure 1 As shown, the plot was created using Origin 2018, and the results showed that the genotype sizes of Reed are: CN2024 > JS02 > SD05 > SD01 > CX01 > CN2028 > G2 > NX25.

[0047] (8) The reeds in the cadmium-treated group were divided into above-ground and underground parts. After weighing the fresh weight of the sample, it was placed in an oven at 105℃ for 30 min to kill the green, then dried at 80℃ to constant weight. After cooling, it was taken out, ground, passed through a 0.5 mm sieve, and 2 g was accurately weighed. The cadmium content in the sample was determined by atomic fluorescence spectrophotometer using the concentrated nitric acid digestion method.

[0048] (9) After measuring the cadmium content in reeds, the translocation coefficient was calculated. The translocation coefficient reflects the plant's ability to translocate heavy metals from the underground parts to the aboveground parts. Translocation coefficient = aboveground cadmium content / underground cadmium content. The translocation coefficients of the eight reed genotypes are shown below. Figure 2 As shown, using Origin2018 to plot, the results show that the sizes of each genotype of reed are: CN2024>JS02>SD05>SD01>CX01>CN2028>G2>NX25, which is consistent with the results calculated by the cadmium transport assessment index in step (7).

[0049] (10) Correlation analysis between the cadmium translocation assessment index and translocation coefficient of reeds, as follows: Figure 3 As shown, the Pearson correlation coefficient was calculated and plotted using the ggstatsplot package (version: 0.11.0.9000) in R (version 4.2.2). The results show that the translocation coefficient and the cadmium translocation assessment index are strongly correlated (r = 0.91, p < 0.01), indicating that the cadmium translocation assessment index has a similar effect on assessing the cadmium translocation capacity of reeds as the translocation coefficient.

[0050] Therefore, without conducting cadmium treatment experiments, the cadmium translocation capacity of reeds can be evaluated simply by measuring their basal diameter, transpiration rate, and stomatal conductance, and calculating the cadmium translocation assessment index. This provides a simple and easy method for quickly and efficiently selecting reed varieties with strong translocation capacity.

Claims

1. A method for evaluating the cadmium translocation capacity of reeds based on plant functional traits, characterized in that: The basal diameter, stomatal conductance, and transpiration rate of normally growing reeds were measured, and the cadmium translocation assessment index was calculated based on these parameters. R =( R 1 + R 2 + R 3 ) / 3, where, R 1 , R 2 , R 3 The evaluation indices are transpiration rate, stomatal conductance, and basal diameter. The cadmium translocation capacity of reeds is assessed using the cadmium translocation index. Based on the measured transpiration rates, the average transpiration rate for each genotype and the maximum transpiration rate among all reeds are calculated. The transpiration rate evaluation index for that genotype is obtained by dividing the average transpiration rate for each genotype by the maximum transpiration rate among all reeds. Similarly, based on the measured stomatal conductance, the average stomatal conductance for each genotype and the maximum stomatal conductance among all reeds are calculated. The stomatal conductance evaluation index for that genotype is obtained by dividing the average stomatal conductance for each genotype by the maximum stomatal conductance among all reeds. Finally, based on the measured basal diameter, the average basal diameter for each genotype and the maximum basal diameter among all reeds are calculated. The basal diameter evaluation index for that genotype is obtained by dividing the average basal diameter for each genotype by the maximum basal diameter among all reeds.

2. The method for evaluating the cadmium transport capacity of reeds based on plant functional traits according to claim 1, characterized in that: Functional traits were measured when reeds reached maturity, at which point the reed height was between 104 and 112 cm.

3. The method for evaluating the cadmium transport capacity of reeds based on plant functional traits according to claim 1, characterized in that: Stomatal conductance and transpiration rate of reeds were measured between 8:00 AM and 12:00 PM, using the first to third leaves from the upper part of the reed, with leaf widths ranging from 0.9 to 1.2 cm.

4. The method for evaluating the cadmium transport capacity of reeds based on plant functional traits according to claim 1, characterized in that: The basal diameter of reeds is the diameter of the stem at the bottom of the plant, 2-5 cm from the soil, measured using vernier calipers.

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