Method for measuring water potential of larch branches under water loss stress in situ

Abstract

The invention discloses a method for in-situ determination of water potential of a water loss stress larch branch, which comprises the following steps: carrying out drought stress treatment on a larch sample branch, continuously shooting branch projection images through an image acquisition device, and calculating projection area loss rate percentages PLA at different water loss time points; measuring a branch water potential drop value psi d at the same time point by using the pressure chamber; fitting a linear regression equation of PLA and psi d as a standard curve; measuring the initial water potential psi o of the larch nursery stock to be measured; fixing an image acquisition device at the original position of the branch, shooting projection images according to a set interval, and calculating real-time PLA; and substituting the real-time PLA into the standard curve to obtain a real-time water potential drop value. According to the method, in-situ, continuous and nondestructive monitoring on the water potential of the larch branches is realized, the defect that destructive sampling is needed in a traditional pressure chamber method is overcome, and the water physiological response of the branches under water loss stress can be dynamically captured; compared with a hygrometer water potential instrument, the method is low in cost, easy and convenient to operate and higher in adaptability to seedlings.

Description

Technical Field

[0001] The present invention relates to the technical field of plant physiological parameter detection, and specifically to a method and device for in-situ non-destructive continuous monitoring of water potential of larch seedlings under water loss stress based on changes in branch morphology. The method and device are applicable to the fields of research on drought response mechanisms of woody plants and water management in seedling cultivation. Background Art

[0002] As a key indicator of plant water status, water potential is of great significance for studying plant-environment interactions and plant physiological and ecological responses. Traditional measurement methods have limitations. For example, the pressure chamber method, while widely used, requires destructive sampling and cannot achieve continuous in-situ monitoring. Thermocouple psychrometers, while capable of in-situ measurement, are not suitable for measuring coniferous seedlings due to their large probe size, high cost, and fragility.

[0003] Larix gmelinii is an important ecological and timber species in Northeast and North my country. Its growth is significantly affected by water conditions. Accurately monitoring the dynamic changes in branch water potential is crucial when studying the responses of woody plants like larch to drought stress. Summary of the Invention

[0004] In view of this, the object of the present invention is to provide a low-cost, efficient and in-situ method for continuously measuring branch water potential suitable for seedlings.

[0005] The inventors have continuously innovated and explored the above technical problems through long-term exploration and attempts, as well as multiple experiments and efforts. The present invention provides a method for in-situ determination of water potential of larch branches under water loss stress, comprising the following steps: 1) Establishing a standard curve: Drought stress treatment was performed on larch sample branches, and the following steps were performed simultaneously: The image acquisition device was used to continuously capture the branch projection images and calculate the projection area loss percentage PLA at different water loss time points. The calculation formula is: ; Determination of the first initial water potential Ψ of branches using a pressure chamber o1 The first real-time water potential of the branches was measured at the same time as the photo was taken. s1 , calculate the first real-time water potential drop value Ψ of the branch d1 ; Ψ d1 = Ψ o1 - Ψ s1 ; Fitting PLA and Ψ d1 The linear regression equation of was used as the standard curve; Fitting PLA and Ψ d1 The linear regression equation of was used as the standard curve; 2) In-situ water potential monitoring: Perform the following on the larch seedlings to be tested: Determination of the second initial water potential Ψ o2 ; The image acquisition device is fixed on the branch in place, and projection images are taken at set intervals and real-time PLA is calculated; Substitute the real-time PLA into the standard curve of step 1) to obtain the second real-time water potential drop value Ψ d2 ; Calculate the second real-time water potential Ψ s2 :Ψ s2 = Ψ o2 - Ψ d2 .

[0006] Compared with the prior art, the present invention has the following beneficial effects: The present invention uses image acquisition and analysis technology, combined with the data measured by the pressure chamber, to establish the relationship between the percentage of projected area loss (PLA) and the decrease in branch water potential (Ψ d ) to achieve in-situ, continuous, and nondestructive monitoring of water potential in larch branches. This method overcomes the destructive sampling requirements of traditional pressure chamber methods and can dynamically capture the water physiological responses of branches under water loss stress. Furthermore, compared to psychrometers, the image acquisition device of this invention is inexpensive, simple to operate, and more adaptable to seedlings. It is not restricted by branch diameter, significantly expanding the technical means for studying tree water physiology, improving measurement efficiency and applicability, and providing a new, efficient and reliable method for measuring water potential in fields such as ecology and forestry.

[0007] On the basis of the above technical solution, the present invention can also be improved as follows: Furthermore: the image acquisition device includes a detection chamber, a photographing component, a clamping component and a support rod; The clamping assembly is used to clamp the branch to be tested, and the clamping assembly is installed on the support rod and has a built-in light source; The photographing assembly is detachably mounted on the clamping assembly.

[0008] Compared with the prior art, the beneficial effects of adopting the above further technical solution are: The present invention achieves stable clamping of branches and precise light source control by integrating the light source into a clamping assembly installed on a support rod and adopting a detachable photographing assembly. It also facilitates the maintenance and replacement of the photographing assembly, improves the stability and flexibility of image acquisition, and thus enhances the accuracy of water potential measurement.

[0009] On the basis of the above technical solution, the present invention can also be improved as follows: Furthermore: the light source is an LED lamp with a diameter of ≤16 mm, and the distance between the lower surface of the branch and the camera assembly is 18±2 mm.

[0010] Compared with the prior art, the beneficial effects of adopting the above further technical solution are: By using a smaller-diameter LED lamp as the light source and precisely controlling its distance from the camera assembly, the device size and cost can be effectively reduced while ensuring the clarity and stability of image acquisition, thereby improving the accuracy and reliability of water potential measurement.

[0011] On the basis of the above technical solution, the present invention can also be improved as follows: Furthermore: the clamping assembly includes a first clamping plate and a second clamping plate, the first clamping plate is provided with a first elastic ring, and the second clamping plate is provided with a second elastic ring; the branch to be tested is clamped and fixed by the first elastic ring and the second elastic ring; the light source is located on the side of the first elastic ring, and the photographing assembly is located on the side of the second elastic ring.

[0012] Compared with the prior art, the beneficial effects of adopting the above further technical solution are: By setting up a clamping component with an elastic ring, it can adapt to branches of different diameters, achieve firm clamping while avoiding damage to the branches, ensure the relative position of the light source and the camera component is stable, and effectively improve the stability and accuracy of image acquisition.

[0013] On the basis of the above technical solution, the present invention can also be improved as follows: Furthermore, the distance between the light source and the camera assembly is adjustable to meet the magnification requirements of branches with different diameters.

[0014] Compared with the prior art, the beneficial effects of adopting the above further technical solution are: By adjusting the distance between the light source and the camera assembly, the imaging requirements of branches of varying diameters can be met, ensuring image clarity and accuracy, thereby improving the applicability and reliability of water potential measurement. Magnification allows for a detailed preview of the projected image of the branch.

[0015] On the basis of the above technical solution, the present invention can also be improved as follows: Furthermore: the branch diameter range is 3-8 mm, the photographing interval is 10-60 min, and the projected image magnification is 1-12 times.

[0016] Compared with the prior art, the beneficial effects of adopting the above further technical solution are: By limiting the branch diameter range, photographing interval and projection image magnification, the applicability and measurement accuracy of the method of the present invention to the target branches are ensured, and the branch projection area change data can be stably obtained under different conditions, thereby improving the reliability and accuracy of water potential measurement.

[0017] On the basis of the above technical solution, the present invention can also be improved as follows: Furthermore: the detection room is a windproof and breathable room with a full-spectrum light source installed inside.

[0018] Compared with the prior art, the beneficial effects of adopting the above further technical solution are: By setting up a windproof and breathable detection room and equipping it with a full-spectrum light source, we can effectively eliminate interference from the external environment, ensure that the lighting during image acquisition is uniform and stable, and that the branches are shake-free, thereby improving image quality and measurement accuracy and enhancing the accuracy of water potential measurement.

[0019] On the basis of the above technical solution, the present invention can also be improved as follows: Furthermore, the calculation of the PLA is based on direct conversion of image pixel area, and the projection outline is extracted by threshold segmentation using Image J software, without converting the actual physical area.

[0020] Compared with the prior art, the beneficial effects of adopting the above further technical solution are: PLA was calculated by direct conversion based on image pixel area and projection contours were extracted using Image J software for threshold segmentation. This simplified the calculation process, avoided errors that might be caused by conversion of actual physical area, improved measurement efficiency and accuracy, and achieved rapid and accurate analysis of branch projection area.

[0021] On the basis of the above technical solution, the present invention can also be improved as follows: Furthermore, the establishment of the standard curve must meet the following requirements: the coefficient of determination R² of the linear regression equation is ≥ 0.95, and the error rate between the predicted water potential value and the actual value measured in the pressure chamber is ≤ 10%.

[0022] Compared with the prior art, the beneficial effects of adopting the above further technical solution are: By strictly limiting the accuracy of the linear regression equation of the standard curve and the error range of the predicted water potential value, the accuracy and reliability of the water potential prediction are significantly improved, ensuring the credibility of the measurement results of the method of the present invention, avoiding measurement deviations caused by poor curve fitting or excessive errors, and providing more precise technical guarantees for practical applications.

[0023] On the basis of the above technical solution, the present invention can also be improved as follows: Furthermore: the linear regression equation is: y=0.5789x-0.0324; Where y is Ψ d , unit is MPa, x is PLA, unit is %, equation determination coefficient R 2 =0.9832.

[0024] Compared with the prior art, the beneficial effects of adopting the above further technical solution are: By providing a specific high-precision linear regression equation, which is directly used to convert the projected area loss rate into the branch water potential decline value, the accuracy and operability of water potential prediction are significantly improved, the error caused by curve fitting uncertainty is reduced, and a more reliable quantitative basis is provided for water potential determination. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0026] Figure 1 This is a reference diagram of the actual application state of a preferred embodiment of the method for in-situ determination of water potential of larch branches under water loss stress of the present invention.

[0027] Figure 2 yes Figure 1 Line diagram of application states.

[0028] Figure 3 1 is a schematic diagram of the branch projection image processing flow in one embodiment of the present invention. Figure 3 Figure a is the original projection image of the branch collected, Figure b is the image of the branch projection image shown in Figure a after 8-bit grayscale conversion using Image J software, and Figure c is the red analysis area image determined after threshold segmentation processing using Image J software in Figure b.

[0029] Figure 4 It is a schematic diagram of the front view structure of the photographing component and the clamping component in one embodiment of the present invention.

[0030] Figure 5 yes Figure 4 Schematic diagram of the explosion structure from a top-down perspective.

[0031] Figure 6 yes Figure 4 Schematic diagram of the three-dimensional explosion structure from an upward perspective.

[0032] The marks in the figure are: 100 testing rooms, 200 support rods, 210 camera components, 211 cameras, 212 positioning screw, 220 clamping assembly, 221 first clamping plate, 222 light source, 223 first elastic ring, 224 second clamping plate, 225 second elastic ring, 226 positioning slots, 300 nutrient pots, 310 plants. DETAILED DESCRIPTION

[0033] The following describes the details in conjunction with specific embodiments.

[0034] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. Therefore, the following detailed description of the embodiments of the present invention is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention.

[0035] In the present invention, unless otherwise specified, all equipment and raw materials can be purchased from the market or are commonly used in the industry. The methods in the following embodiments, unless otherwise specified, are all conventional methods in the art.

[0036] Example 1 The method described in this example for in situ determination of water potential of larch branches under water loss stress uses an image acquisition device, see Figures 1 and 2 、 Figures 4-6 , the specific structure is as follows: The image acquisition device consists of a detection chamber 100, a camera assembly 210, a clamping assembly 220, and a support rod 200. The detection chamber 100 is a windproof and breathable room, such as a light incubator, equipped with a full-spectrum light source. This effectively eliminates external environmental interference and ensures uniform and stable illumination during image acquisition, thereby improving image quality and measurement accuracy, and enhancing the accuracy of water potential measurements.

[0037] The clamping assembly 220 is mounted on the support rod 200 and includes a built-in light source 222. Its primary function is to clamp the branch to be tested. The clamping assembly 220 includes a first clamping plate 221 and a second clamping plate 224. The first clamping plate 221 is provided with a first elastic ring 223, and the second clamping plate 224 is provided with a second elastic ring 225. The branch to be tested is clamped and fixed by the first elastic ring 223 and the second elastic ring 225. This clamping assembly 220 with elastic rings can accommodate branches of varying diameters, achieving a secure clamp while avoiding damage to the branch. This ensures a stable relative position between the light source 222 and the camera assembly 210, effectively improving the stability and accuracy of image acquisition.

[0038] The camera assembly 210 is detachably mounted on the clamping assembly 220, facilitating maintenance and replacement of the camera assembly 210. In one embodiment, the camera assembly 210 is detachably mounted on the clamping assembly 220 and includes a camera 211 and a positioning screw 212. The second clamping plate 224 is provided with a positioning slot 226, into which the positioning screw 212 slidably engages, thereby adjusting the distance between the camera 211 and the branch. Once adjusted, the camera 211 is secured with a positioning nut. This design allows for flexible adjustment of the distance between the camera and the branch based on the branch diameter and actual measurement requirements, ensuring image clarity and accuracy.

[0039] The light source 222 used by the camera assembly 210 is an LED lamp with a diameter of ≤16 mm. The distance between the lower surface of the branch and the camera assembly 210 is 18 ± 2 mm. By using a smaller diameter LED lamp as the light source 222 and precisely controlling its distance from the camera assembly 210, the device size and cost can be effectively reduced while ensuring the clarity and stability of image acquisition, thereby improving the accuracy and reliability of water potential measurement.

[0040] The distance between the light source 222 on the clamping assembly 220 and the camera assembly 210 is adjustable to accommodate the magnification requirements of branches of varying diameters. Adjusting the distance between the light source 222 and the camera assembly 210 allows for imaging of branches of varying diameters, ensuring clarity and accuracy in image capture, thereby improving the applicability and reliability of water potential measurement.

[0041] The applicable branch diameter range is 3-8 mm, the imaging interval is 10-60 minutes, and the projection image magnification is 1-12 times. By limiting the branch diameter range, imaging interval, and projection image magnification, the method ensures its applicability and measurement accuracy for target branches. It can stably obtain branch projection area change data under different conditions, thereby improving the reliability and accuracy of water potential measurement.

[0042] The camera assembly 210 captures branch projection images at regular intervals and transmits the captured images to a computer via a data cable. Image J image processing software is used to analyze the branch projection area and obtain a series of branch area data. The specific image processing process is as follows: S1, the collected original projection image of the branch ( Figure 3 (a) After 8-bit grayscale conversion using Image J software, the grayscale image was obtained ( Figure 3 Middle b).

[0043] S2, perform threshold segmentation on the grayscale image to determine the red analysis area ( Figure 3 C in the middle), thereby extracting the projection outline of the branch.

[0044] S3. Calculate the projected area of ​​the branch by counting pixel areas and calculate the percentage loss of area (PLA) at different water loss times using a formula. Because repeated in-situ photography captures the same area, the percentage loss can be calculated directly from pixel areas, eliminating the need to convert to actual physical area. This simplifies the calculation process, avoids potential errors associated with converting to actual physical area, improves measurement efficiency and accuracy, and enables rapid and accurate analysis of the projected area of ​​the branch.

[0045] Example 2 This example describes a method for in situ measurement of water potential in dehydration-stressed larch branches using the apparatus described in Example 1. In this example, the distance from the lower surface of the branch to the camera is 18 mm, the light source is a 16 mm diameter LED lamp, and the projected image magnification is 10x. Of course, any existing device capable of securing a camera and light source may be used, as long as the light source and camera can be secured to the branch and capable of continuous and stable image capture and detection.

[0046] 1. Experimental Preparation In this embodiment, 3-year-old Larix principis-rupprechtii seedlings grown in sand culture containers are selected as experimental materials. That is, Larix principis-rupprechtii plants 310 are planted in nutrient pots 300 and cultured in a light incubator (testing room 100) to ensure that the seedlings grow in a suitable environment and facilitate subsequent drought stress treatment.

[0047] According to Example 1, the image acquisition device was assembled and mounted on a 5 mm diameter branch of Larix principis-rupprechtii. The clamping assembly was ensured to firmly hold the branch and the camera assembly was properly positioned to capture a clear projection image of the branch.

[0048] Before stopping watering for drought stress treatment, the initial water potential (Ψo) of the branches was measured using a pressure chamber and recorded as the basic data for subsequent calculation of real-time water potential.

[0049] 2. Establish a standard curve 2.1 Drought stress treatment and image acquisition Watering was stopped for the sample branches of Larix principis-rupprechtii, allowing them to undergo natural drought stress. Simultaneously, an image acquisition device was activated, with a shooting interval set to capture a branch projection image every 30 minutes. This was continued for several days to obtain branch projection images at different time points of water loss.

[0050] 2.2 Calculation of projected area loss rate The captured branch projection images were transferred to a computer and analyzed using Image J. The images were first converted to 8-bit grayscale images, and then the branch projection outlines were extracted using the threshold segmentation method. The projection pixel areas were then counted (see Table 1).

[0051] According to the formula , calculate the percentage of projected area loss (PLA) at different water loss time points, see Table 1.

[0052] Table 1 Data on branch projection area and water potential at different water loss times 2.3 Determination of water potential drop During drought stress, water potential measurements were performed on twigs using a pressure chamber at different time points. The branch water potential values ​​at each time point were obtained by subtracting the initial water potential value (Ψo) from the branch water potential value at each time point to obtain the corresponding water potential drop (Ψd). See Table 2: Ψd = Ψo (negative value) - branch water potential at different time points of water loss stress (negative value). Note that Ψo is the initial water potential value, which is typically negative, so signed arithmetic is important for calculations.

[0053] Table 2 Data on branch projected area loss rate and water potential drop at different water loss times 2.4 Linear regression equation fitting Collect PLA values ​​and corresponding Ψd values ​​at multiple different water loss time points. With PLA as the independent variable and Ψd as the dependent variable, plot a scatter plot in a coordinate system and fit a linear regression equation between the two. The linear regression equation must have a coefficient of determination (R²) ≥ 0.95, and an error rate of ≤ 10% between the predicted water potential and the measured value in the pressure chamber to ensure the accuracy and reliability of the standard curve. In this example, the fitted linear regression equation is y = 0.5789x - 0.0324, where y is Ψd (in MPa) and x is PLA (in %). The equation has a coefficient of determination (R²) of 0.9832.

[0054] 3. In-situ water potential monitoring 3.1 Determination of initial water potential For the tested Larix principis-rupprechtii seedlings, the initial water potential Ψo of their branches was measured using a pressure chamber, and the value was accurately recorded to provide a benchmark for subsequent water potential calculations.

[0055] 3.2 Image acquisition and PLA calculation Secure the image acquisition device to the original location of the test seedling branch and continuously capture branch projection images at a pre-set interval (e.g., every 30 minutes). Maintain the device's stability during capture to ensure image clarity and accuracy. Transfer the captured images to a computer and calculate the real-time percentage loss of projected area (PLA) at each time point using Image J software, following the image processing methods described above for establishing the standard curve.

[0056] 3.3 Real-time water potential calculation The calculated real-time PLA value is substituted into the linear regression equation corresponding to the established standard curve to determine the water potential drop value Ψd at that point in time. The water potential value Ψs of the branch under real-time water loss is then calculated according to the formula Ψs (-MPa) = Ψo (negative value) - Ψd (positive value), thereby achieving in-situ, continuous, and non-destructive monitoring of the water potential of larch branches. Throughout the monitoring process, the physiological state changes of the branches and the operation of the image acquisition device are closely observed to ensure the accuracy and reliability of the monitoring data. This provides real-time, dynamic data support for the study of the water physiological response of larch under drought stress, facilitates a deeper understanding of its drought resistance mechanism, and provides a scientific basis for forest cultivation and management.

[0057] Example 3 This example uses the sand culture natural water loss method to verify the effectiveness of the method of the present invention.

[0058] Another Larix principis-rupprechtii was selected and treated with the same sand culture natural water loss and drought method used to establish the standard curve.

[0059] During the treatment process, the water potential was measured using both the method of measuring water potential based on area change in Example 2 and the conventional pressure chamber method. The water potential prediction value obtained by the area change measurement method was compared with the actual water potential value measured by the pressure chamber, and the error rate at each time point was calculated using the following formula: See Table 3 for the results.

[0060] Table 3 Comparison of water potential of naturally dehydrated Larix principis-rupprechtii branches in sand culture and the actual water potential Note: 1. The actual water potential value is measured using a conventional pressure chamber; 2. The projected area measured at 9:28 is the initial area, and the actual water potential value is the initial water potential.

[0061] It has been verified that the average error at each time point is only 1.88%, indicating that the measurement method of the present invention has high accuracy.

[0062] Example 4 This example uses the pot-dehydration method to verify the effectiveness of the method of the present invention.

[0063] The seedlings were removed from the sand culture medium with their roots intact, placed in a laboratory under shaded conditions to dehydrate. The branch area was measured using the same method as in Example 2, and the corresponding water potential predictions were calculated using a standard curve. These predictions were then compared with the actual water potential values ​​measured in a conventional pressure chamber. The results are shown in Table 4.

[0064] Table 4 Comparison of water potential of Larix principis-rupprechtii branches after natural dehydration and the actual water potential Note: The actual water potential value is measured using a conventional pressure chamber.

[0065] Although the average error rate of the method of the present invention is slightly higher, at 5.938%, it is still within an acceptable range, which further proves the effectiveness and feasibility of the method for measuring water potential based on changes in branch projection area. It can be used to measure the water potential of larch branches, especially in field monitoring or long-term continuous monitoring scenarios where the pressure chamber method cannot be used frequently. It has unique advantages and application value.

[0066] In the description of the present invention, it should be understood that "-" and "~" represent a range between two values, and the range includes the endpoints. For example, "AB" represents a range greater than or equal to A and less than or equal to B. "A~B" represents a range greater than or equal to A and less than or equal to B.

[0067] In the description of the present invention, the term "and / or" is merely a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B may represent three situations: A exists alone, A and B exist at the same time, and B exists alone.

[0068] In the description of the invention, the numerical values ​​of time, temperature, ratio and mass involved may be based on actual measurements, standard parameters of equipment, simplified rounding results, or within an acceptable error range, ensuring the practicality and repeatability of the invention.

[0069] In the description of the present invention, the term "about" or "approximately" is used to express the approximate value of a numerical value or range, allowing a certain error to ensure the flexibility and practicality of the description while remaining within an acceptable error range, with the maximum error range not exceeding 10% of the corresponding numerical value or numerical range.

[0070] The above are merely preferred embodiments of the present invention. It should be noted that the above preferred embodiments should not be construed as limiting the present invention, and the scope of protection of the present invention should be determined by the scope defined in the claims. Persons skilled in the art will appreciate that improvements and modifications may be made without departing from the spirit and scope of the present invention, and such improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for in situ determination of water potential of larch branches under water loss stress, characterized in that: The following steps are involved: 1) Establishing a standard curve: Drought stress treatment was performed on larch sample branches, and the following steps were performed simultaneously: The image acquisition device was used to continuously capture the branch projection images and calculate the projection area loss percentage PLA at different water loss time points. The calculation formula is: ； Determination of the first initial water potential Ψ of branches using a pressure chamber o1 The first real-time water potential of the branches was measured at the same time as the photo was taken. s1 , calculate the first real-time water potential drop value Ψ of the branch d1 ; P d1 = Ψ o1 - P s1 ; Fitting PLA and Ψ d1 The linear regression equation of was used as the standard curve; 2) In-situ water potential monitoring: For the larch seedlings to be tested: Determination of the second initial water potential Ψ o2 ; The image acquisition device is fixed on the branch in place, and projection images are taken at set intervals and real-time PLA is calculated; Substitute the real-time PLA into the standard curve of step 1) to obtain the second real-time water potential drop value Ψ d2 ; Calculate the second real-time water potential Ψ s2 :Ψ s2 = Ψ o2 - Ψ d2 .

2. The method for in-situ determination of water potential of larch branches under water loss stress according to claim 1, characterized in that The image acquisition device includes a detection chamber, a photographing component, a clamping component and a support rod; The clamping assembly is used to clamp the branch to be tested, and the clamping assembly is installed on the support rod and has a built-in light source; The photographing assembly is detachably mounted on the clamping assembly.

3. The method for in-situ determination of water potential of larch branches under water loss stress according to claim 2, characterized in that: The light source is an LED lamp with a diameter of ≤16 mm, and the distance between the lower surface of the branch and the camera assembly is 18±2 mm.

4. The method for in-situ determination of water potential of larch branches under water loss stress according to claim 2, characterized in that: The clamping assembly includes a first clamping plate and a second clamping plate, the first clamping plate is provided with a first elastic ring, and the second clamping plate is provided with a second elastic ring; the branch to be tested is clamped and fixed by the first elastic ring and the second elastic ring; the light source is located on the side of the first elastic ring, and the photographing assembly is located on the side of the second elastic ring.

5. The method for in-situ determination of water potential of larch branches under water loss stress according to claim 2, characterized in that: The distance between the light source and the photographing component is adjustable to meet the magnification requirements of branches with different diameters.

6. The method for in-situ determination of water potential of larch branches under water loss stress according to claim 1 or 5, characterized in that: The branch diameter ranged from 3 to 8 mm, the photographic interval was 10 to 60 min, and the projected image magnification was 1 to 12 times.

7. The method for in-situ determination of water potential of larch branches under water loss stress according to claim 2, characterized in that: The detection room is a windproof and ventilated room with a full-spectrum light source installed inside.

8. The method for in-situ determination of water potential of larch branches under water loss stress according to claim 1, characterized in that: The calculation of PLA is based on direct conversion of image pixel area, and the projection outline is extracted by threshold segmentation using Image J software without converting the actual physical area.

9. The method for in-situ determination of water potential of larch branches under water loss stress according to claim 1, characterized in that: The establishment of the standard curve must meet the following requirements: the coefficient of determination R² of the linear regression equation is ≥ 0.95, and the error rate between the predicted water potential value and the actual value measured in the pressure chamber is ≤ 10%.

10. The method for in-situ determination of water potential of larch branches under water loss stress according to claim 9, characterized in that: The linear regression equation is: y=0.5789x-0.0324; Where y is Ψ d , unit is MPa, x is PLA, unit is %, equation determination coefficient R 2 =0.9832.

Images