WO2005059542A1

WO2005059542A1 - A method and an apparatus for monitoring the water potential of living plant in situ

Info

Publication number: WO2005059542A1
Application number: PCT/CN2004/001473
Authority: WO
Inventors: Ximin Deng
Original assignee: Ximin Deng
Priority date: 2003-12-19
Filing date: 2004-12-20
Publication date: 2005-06-30
Also published as: CN1611930A

Abstract

The present invention relates to an apparatus for monitoring the water potential of living plant in situ, comprising a device for measuring the average water flow rate in plant duct, a device for measuring water flow flux in plant duct, and a plant water potential calculating device. The invention further relates to a method for monitoring the water potential of living plant in situ, comprising the steps of: determining the water flow flux in plant duct J and the average water flow rate v; determining the differential water pressure P by the water flow flux in plant duct J and the average water flow rate v, P=8πηv2/J; and determining the water potential of plant by the differential water pressure P. The invention may be used for real-time monitoring the water potential of living plant in situ conveniently and cheaply, without special requirement to the applied environment.

Description

Method and device for monitoring water potential of living plants in situ

The invention relates to the technical field of plant moisture determination, in particular to a method and a device for monitoring the water potential of living plants in situ. Background of the invention

Water is one of the most abundant and important substances in plants. Water not only affects the type and distribution of ground vegetation, but also extremely importantly affects the growth, yield and quality of various crops, flowers and trees. Therefore, the research on the relationship between plant moisture has been the focus of widespread attention.

Plant water potential is defined as: Chemical potential difference per unit molar volume of water. It indicates the difference in free energy between a unit volume of water and an equal volume of pure water in a plant. It is a basic measure of the water status of a plant and is also one of the important indicators for measuring the degree of water deficiency in a plant. For a long time, people have been exploring the method of measuring the water potential of plants. At present, the main methods for measuring plant water potential are: the method of measuring plant water potential using the principle of pressure balance, the method of measuring plant water potential using the principle of water vapor pressure balance, and the method of directly measuring plant water potential using precision pressure instruments. Correspondingly, there are measuring devices such as pressure chamber water potential meter, thermocouple water potential meter and pressure probe water potential measuring equipment.

The pressure chamber water potential meter uses the principle of pressure balance to determine the water potential of leaves or branches of plants. Put the sprouts or leaves cut from the plant into the pressure chamber, and the ends of the sprouts are exposed to the outside through the small holes in the gasket, and air pressure is applied in the pressure chamber to return the water in the plant material to the end incision. It is generally believed that at this time, the applied pressure is equal to the absolute value of the water potential of the plant body. The principle of this method is relatively simple and easy to operate, but it is not possible to continuously monitor the water potential of living plants, and the number of measurements is limited by the amount of plant material.

Thermocouple water potentiometer uses the principle of water vapor pressure balance to determine the dew point temperature, so as to determine the in vitro Water potential of plant materials. This method also cannot monitor the water potential of living plants, and it has very strict requirements on the stability of the measured ambient temperature. Small changes in temperature will have a great impact on the measurement results, and it takes a long time for the plant material to reach the water vapor pressure equilibrium. Therefore, it is not conducive to practical application.

There is also a pressure probe measuring device for determining the water potential of plants. The micro-pressure probe in the device was directly inserted into the plant xylem conduit, and the pressure sensor connected to the probe was used to directly measure the negative pressure of the conduit water to determine the water potential. This device can continuously monitor the water potential of living plants, but because the fine probes are inserted directly into very thin plant conduits, the operation requirements are very strict, it is very difficult to use, and because the device is very fine, the price is very high. It is expensive and cannot be applied in actual production. Moreover, due to the limitation of basic physical laws, the catheter fluid is extremely easy to vaporize under low negative pressure to generate air bubbles, blocking the connection between the catheter fluid and the pressure probe liquid level. Therefore, the measurement limit of this device can only reach-0.7 MPa. In many cases, the actual measurement needs cannot be met. Summary of the invention

In view of this, on the one hand, the present invention provides a method for monitoring the water potential of living plants in situ, and the method can be used for simple and continuous continuous monitoring of the water potential of living plants.

Another aspect of the present invention provides a device for monitoring the water potential of living plants in situ. The device is capable of simply and continuously monitoring the water potential of living plants in situ.

According to the above purpose, the technical solution of the present invention is implemented as follows:

A device for monitoring the water potential of living plants in situ includes: a device for measuring the average water flow velocity of a plant tube, a device for measuring the water flow of a plant tube, and a device for calculating a plant water potential, wherein:

Plant pipe average water flow velocity measuring device, for measuring the average water flow velocity flowing through the pipe of the plant material under test; Plant conduit water flow measurement equipment for measuring water flow through a pipe of a plant material under test;

Plant water potential calculation equipment, which calculates the water potential of the plant under test according to the water flow and average water flow speed;

The plant conduit average water velocity measurement device is connected to the plant water potential calculation device, and the plant conduit water flow measurement device is connected to the plant water potential calculation device.

The plant conduit average water flow velocity measuring device includes: a pulse signal generating unit, a pulse signal receiving unit, and a timer, wherein:

A pulse signal generating unit configured to inject a pulse signal to a first point of the plant material under test; a pulse signal receiving unit configured to receive the pulse signal at a second point of the plant material under test;

A timer, configured to count the time when the pulse signal is transmitted from the first point to the second point;

The timer is respectively connected to the pulse signal generating unit and the pulse signal receiving unit, and is connected to the plant water potential calculation device.

The pulse signal generating unit is a thermal pulse signal generator.

The pulse signal generating unit is an isotope pulse signal generator.

The thermal pulse signal receiving device is a thermocouple temperature probe or a platinum resistance temperature probe.

The isotope pulse signal generator is an isotope solution injector, and the isotope emits beta rays or gamma rays.

The isotope pulse signal receiving device is a radioisotope counting detector.

The plant conduit water flow measurement device is a capillary transpiration meter, or a thermal diffusion stem flow meter, or a thermal equilibrium stem flow meter, or a plant transpiration tester, or a plant osmometer.

A method for monitoring the water potential of living plants in situ, the method includes the following steps: A. Determine the water flow volume J and the average water flow velocity V of the plant conduit of the tested plant material;

B. Determine the water pressure difference P according to the water flow J of the single duct of the plant material to be tested and the average water flow velocity V of the plant duct, where P = -8 n ^ ² / J, π is the circumference, and η is the viscosity coefficient of water;

C Determine the plant water potential based on the water pressure difference P.

The average water flow velocity of the plant conduit determined in step A is:

Al l, inject a pulse signal at the first point of the plant material under test, and record the first moment of the pulse signal;

A12. Receive the pulse signal at a second point of the plant material under test, and record the second moment when the pulse signal is received;

A13: Divide the difference between the distance between the first point and the second point by the difference between the time at the second moment and the first moment to determine the average water flow velocity of the plant duct.

The determination of the water flow of a single plant conduit as described in step A is:

A21: Cut a section of the plant material under test, and measure the total water flow of all the pipes of the plant material under test;

A22. Observe the cut cross-section of the plant material to determine the number of ducts of the plant material to be tested; A23 Determine the water flux of a single plant duct according to the total water flow of all the ducts of the plant material to be tested and the number of ducts of the plant material to be tested.

The water flow of a single plant conduit as described in step A is:

A31: Cut a section of the tested plant material, and determine the water flow velocity and the total water flow of the cut plant material under the condition of set water pressure difference;

A32. Determine the number of ducts of the tested plant from the obtained water flow velocity and total water flow of the cut plant material and a set water pressure difference calculation;

A33. Determine the water flow of a single plant duct according to the total water flow of all plant ducts of the plant material being tested and the number of plant ducts being tested. The pulse signal is a thermal pulse signal.

The pulse signal is an isotope pulse signal.

The isotope pulse signal is a radioisotope instantaneous signal that emits beta rays or gamma y rays.

The water potential of the plant determined according to the water pressure difference P in step C is: + G, where ψ is the water potential of the plant, Π is the permeation potential of the duct solution, and G is the gravitational potential of the duct fluid.

The determination of the plant water potential according to the water pressure difference P in step C is: The absolute value of the plant water potential is proportional to the absolute value of the water pressure difference.

It can be seen from the above technical solutions that the device for monitoring the water potential of living plants in situ provided by the present invention includes a plant conduit average water flow velocity measurement device, a plant conduit water flow measurement device, and a plant water potential calculation device. The plant conduit average water flow velocity measurement device measures the average water flow velocity through the plant conduit; the plant conduit water flow measurement equipment measures the water flow through the plant conduit; the plant water potential calculation device calculates the plant based on the plant conduit water flow and average water flow speed Water potential. Therefore, the present invention achieves continuous monitoring of plant water potential in situ by measuring the average water flow velocity and water flow flux of the plant conduit. Moreover, since the measurement of the water flow velocity and water flow of the plant duct of the present invention is performed directly on the plant under test, the in situ monitoring of the water potential of a living plant is achieved. In addition, the measurement process has no special requirements on external environmental conditions, and the operation is very simple. In addition, the cost of the equipment used in the present invention is very low, thereby greatly reducing the total cost, which is very conducive to widespread promotion and application.

At the same time, the present invention proposes a method for monitoring the water potential of living plants in situ. The method realizes continuous monitoring of the water potential of living plants in situ by measuring the average water flow velocity and water flow of the plant duct. At the same time, since the lower measurement limit of the present invention is a water potential value when the water in the plant body is forced to stop flowing completely, compared with the prior art, the lower measurement limit of the present invention is also improved. The application of this method can realize the continuous measurement of the water potential of living plants in situ, and the measurement process has no special requirements on external environmental conditions, and the operation is very simple. Brief description of the drawings

FIG. 1 is a flowchart of a method for monitoring the water potential of living plants in situ according to the present invention.

FIG. 2 is a schematic diagram of an apparatus for monitoring the water potential of a living plant in situ according to the present invention.

FIG. 3 is a schematic diagram of an apparatus for monitoring water potential of a living plant in situ according to an embodiment of the present invention. Mode of Carrying Out the Invention

In order to make the objectives, technical solutions, and advantages of the present invention clearer and clearer, the following further describes the present invention in detail with reference to the embodiments and the accompanying drawings.

According to the Hagen-Poiseuille law in fluid mechanics, the water flow through a single tube in the xylem of a plant is proportional to the water pressure difference P:

J = AV / At = -PπΓ ⁴ / 8η (1) In the formula (1), At represents the time interval, Δν represents the volumetric water flow through a single conduit within the time interval At, π is the circumference, and r is the radius of the conduit , Η is the viscosity coefficient of water.

Water flow density is the water flow through unit duct area A per unit time, and its value is equal to the average water flow velocity of the duct.

J _V = AV / (Δΐ χ A) = ν = -ΡΓ ² / 8η (2)

Ρ = -ν8η / Γ ² (3)

Because the cross-sectional area of a single duct is A = rr ² , so _r ² = ^ / 7T, and substituted into equation (3), we get:

Ρ = -8π-η / Α (4)

According to the definition of the water flow volume J and the average water flow velocity V of a single duct, we have A = J / i. Substituting into the formula (4), we get

P = -8 ^ v ² / J (5)

Therefore, it can be concluded from equation (5) that if the water flow of a single pipe is determined J and average water velocity ^ can calculate the water pressure difference p.

The water pressure difference P and the plant water potential Ψ have the following relationship:

ψ = ρ-π + σ (6)

In formula (6), Π is the catheter fluid permeation potential, and G is the catheter fluid gravity potential. Therefore, after the water pressure difference P, the osmotic potential of the duct fluid Π, and the gravitational potential G of the duct fluid are determined, the plant water potential Ψ can be obtained according to the correlation between the water potential and the water pressure differential. Preferably, when the vertical height between two points is not large, the values of Π and G are usually very small, and both can be ignored. Then, to simplify the calculation, the absolute value of the water potential ψ can be approximately equal to the absolute value of the water pressure difference P.

FIG. 1 is a flowchart of a method for monitoring the water potential of living plants in situ according to the present invention. As shown in Figure 1, it includes the following steps:

Step 101: Determine the water flow capacity J and the average water flow speed V of the plant conduit of the tested plant material.

Here, the average water flow velocity v of the plant duct can be determined by various methods. For example: A pulse signal is added to the plant catheter fluid, and then the average water velocity v of the catheter is determined by measuring the transmission speed of the pulse signal in the plant catheter fluid. Preferably, the pulse signal may be a thermal pulse signal or an isotope pulse signal.

When the thermal pulse signal is added to determine the average water flow velocity V of the catheter, the two temperature probes can be inserted into the xylem of the plant at a certain distance d, and then the resistance of the thermal pulse signal generator is used to instantly heat the plant catheter fluid and inject a small The heat pulse, and then record the time when the heat pulse passes the two temperature probes ^ and ^ respectively. Then the average water flow velocity V of the plant duct can be obtained by the formula (7):

v = dl (t _x -t ₂ ) (7)

Here, only one temperature probe can be inserted, and the average water flow velocity v of the plant conduit can be determined by measuring the distance between the temperature probe and the resistance pulse thermal pulse signal generator and the time when the temperature probe detects the thermal pulse signal. Preferably, whether using a temperature probe or With two or more temperature probes, both thermocouple temperature probes made by welding two different metal wires or alloy wires can be used to measure the thermal pulse signal.

Adding a heat pulse to the plant duct fluid will affect the water viscosity coefficient, and the heat pulse will also affect the water flow to a certain extent. In order to reduce this effect, the strength and length of the heat pulse signal can be adjusted by adjusting the resistance value, energization time, voltage, and current of the heating resistor in the resistance wire heat pulse signal generator, so as to change the heat pulse to water viscosity coefficient. The effect of water flow is minimized.

In addition to adding a thermal pulse signal to determine the average water flow velocity V flowing through the catheter, the average water flow velocity V of the catheter can also be determined by injecting a trace amount of a radioisotope solution into the plant catheter fluid. Similarly, at this time, a radioactive isotope solution syringe is first used to inject a small amount of radioactive isotope solution into a plant catheter, and then a radioisotope counting detector is used to measure the time at which the isotope pulse signal passes between two points separated by a certain distance d and ₂ That is, the average moving speed of the isotope pulse signal is calculated according to formula (7), which is also the average water flow velocity ν of the plant duct. Preferably, the isotope pulse signal is an instantaneous signal generated by a radioactive isotope capable of emitting beta () rays or gamma () rays.

The water flow J of a single pipe can be determined according to the following formula (8):

J = ∑j / N (8)

Where is the total water flow of all ducts of the plant material under test, and N is the number of ducts of the plant material under test. Preferably, the tested plant material is a leaf vein, or petiole, or a branch, or a stem.

Similarly, various methods can be used to measure the total water flow through the plant duct. For example, measurement is performed using a capillary transpiration meter, or a thermal diffusion stem flow meter, or a thermal equilibrium stem flow meter, or a plant transpiration meter, or a plant lysimeter. Here, it is preferable to use a capillary transpiration meter to measure the total water flow of the plant material conduit. When using a capillary transpiration meter to measure the total water flow of a plant conduit _Σ , the petioles or branches of the plant under test are first cut off in water, and the capillary end is connected to the capillary transpiration meter, and the catheter is measured by measuring the liquid level movement of the capillary transpiration meter per unit time. Total water flow. Optionally, the capillary transpiration meter may be connected to a device such as a weight sensor to measure the weight change of water per unit time, and then calculate the total water flow of the duct _Σ according to the specific gravity of the water _;

Because the total number of ducts of the petiole or branch of the cut plant is equal to or approximately equal to the total number of ducts of the petiole or branch of the plant to be tested, the cross section of the cut petiole or branch of the plant can be observed with a microscope to determine its duct Number N. In addition, the water flow velocity and total water flow 2 of a cut piece of plant material can also be measured under a set water pressure differential condition, and then the number of ducts N can be calculated according to Hagen-Poiseuille's law.

After the total water flow of the plant duct ^ / and the number of ducts N of the plant under test are determined, the water flow J of a single duct can be calculated according to formula (8).

Step 102: According to the water flow J and the average water flow velocity of a single duct! Determine water pressure difference

P.

At this time, based on the formula (5), can the water pressure difference be determined? . That is, P = -8 / την ² /]. Step 103: Determine the plant water potential according to the water pressure difference P.

After the water pressure difference P is obtained, based on the formula (6), the plant water potential Ψ can be determined. That is, Ψ = P-Π + σ. Here, when the vertical height between the two points is not large, ignore Π and G, that is, the absolute value of the water potential Ψ is proportional to the absolute value of the water pressure difference P.

Based on the method shown in FIG. 1, FIG. 2 is a schematic diagram of an apparatus for monitoring the water potential of living plants in situ according to the present invention. As shown in FIG. 2, the device includes a plant conduit average water flow velocity measurement device 201, a plant water potential calculation device 202, and a plant conduit water flow measurement device 203. Among them, a plant conduit average water flow velocity measuring device 201 is used to measure the mean water flow velocity of the plant conduit passing through the tested plant material 204; a plant conduit water flow measuring device 203 is used to measure the plant The total water flow of the material pipe; The plant water potential calculation device 202 calculates the plant water potential based on the water flow of the plant pipe and the average water flow velocity. The tested plant material 204 is connected to a plant duct average water flow velocity measurement device 201 and a plant duct water flow measurement device 203. The plant water potential calculation device 202 is connected to the plant conduit average water flow velocity measurement device 201, and the plant water potential calculation device 202 is connected to the plant conduit water flow measurement device 203. The tested plant material includes leaf veins, petioles, branches, or stems.

Preferably, the plant conduit average water flow velocity measuring device 201 includes: a pulse signal generating unit, a pulse signal receiving unit, and a timer, wherein the pulse signal generating unit is configured to inject a pulse signal to a first point of the plant material under test; the pulse signal The receiving unit is configured to receive the pulse signal at the second point of the tested plant material; and the timer is used to time the time when the pulse signal is transmitted from the first point to the second point. The timer is connected to the pulse signal receiving unit and the pulse signal generating unit, respectively. The timer is connected to the plant water potential calculation device 202. More preferably, the pulse signal generating unit is a thermal pulse signal generating unit or an isotope pulse signal generating unit. When the pulse signal generating unit is an isotope pulse signal generating unit, the isotope pulse signal generating unit preferably injects a radioactive isotope solution capable of emitting beta () ray or gamma () ray pulse signals into the tube of the plant material under test, and isotope pulse signal receiving equipment It is a radioisotope counting detector. When the pulse signal generating unit is a thermal pulse signal generating unit, the thermal pulse signal generating unit is a resistance wire thermal pulse signal generator, and the thermal pulse signal receiving device may be a thermocouple temperature probe, a platinum resistance temperature probe, or other thermal appliances element.

The plant conduit water flow measurement device 203 may be a capillary transpiration meter, or a thermal diffusion stem flow meter, or a hot-level street stem flow meter, or a plant transpiration tester, or a plant osmometer. A capillary transpiration meter is preferred.

The plant water potential calculation device 202 calculates the plant water based on the water flow measured by the water flow measurement device 203 and the average water flow speed measured by the average water flow speed measurement device 201 Potential. The plant water potential calculation device 202 may be a single chip computer or a PC. Optionally, the plant water potential calculation device 202 is connected to the plant conduit average water flow speed measurement device 201 to obtain the plant conduit average water flow speed measurement device 201 to measure the plant conduit average water flow speed measurement device 201. The plant conduit water flow measured by the plant conduit water flow measurement device 203 may be manually input in the plant water potential calculation device 202 to finally calculate the plant water potential. At this time, the plant water potential calculation device 202 may not be connected to the plant conduit water flow measurement device 203. In addition, the plant water potential calculation device 202 may also be connected to the plant conduit water flow measurement device 203 to obtain the plant conduit water flow in real time and calculate the plant water potential. Optionally, the plant water potential calculation device 202 and the plant conduit average water flow velocity measurement device 201 may not be connected. At this time, the plant water potential calculation device 202 may manually input the average water velocity of the plant tube measured by the plant tube average water flow velocity measurement device 201 to finally calculate the plant water potential. The plant water potential calculation device 202 and the plant conduit average water flow speed measurement device 201 may also be connected to obtain the plant conduit average water flow speed in real time, and calculate and obtain the plant water potential.

Based on the apparatus shown in FIG. 2, FIG. 3 is a schematic diagram of an in-situ monitoring device for water potential of a living plant according to an embodiment of the present invention. As shown in FIG. 3, the device includes a thermal pulse signal generator 301, a thermal pulse signal injection needle 302, a first thermal pulse signal receiving needle 303, a second thermal pulse signal receiving needle 304, a thermal pulse signal acquisition instrument 305, and a plant water potential. The calculation unit 306 and the capillary transpiration apparatus, wherein the capillary transpiration apparatus includes a water container 307, a sealant plug 308, and a capillary 309. The thermal pulse signal generator 301, the thermal pulse signal injection needle 302, the thermal pulse signal acquisition instrument 305, the first thermal pulse signal receiving needle 303, and the second thermal pulse signal receiving needle 304 correspond to the average water flow velocity measurement of the plant catheter in FIG. 2 Equipment 201. The capillary transpiration apparatus corresponds to the plant conduit water flow measurement device 203 in FIG. 2. The plant water potential calculation unit 306 corresponds to the plant water potential calculation device 202 in FIG. 2.

The thermal pulse signal generator 301 generates a thermal pulse; the thermal pulse signal is injected into the needle 302, and the thermal pulse is injected into the xylem of the petiole 310 of the plant under test. Measuring the leaf veins, petioles, branches or stems of plants; the first heat pulse signal receiving needle 303 and the second heat pulse signal receiving needle 304 respectively receive the heat pulse signal; the heat pulse signal collector 305 calculates the first heat pulse signal reception The time difference between the needle 303 and the second thermal pulse signal receiving needle 304 receiving the thermal pulse. Based on the time difference and the distance between the first thermal pulse signal receiving needle 303 and the second thermal pulse signal receiving needle 304, the average water velocity of the plant conduit was calculated. And sends a signal of the average velocity of the plant conduit to the plant water potential calculation unit 306. Here, preferably, the first thermal pulse signal receiving needle 303 and the second thermal pulse signal receiving needle 304 are both thermocouple temperature probes.

The petiole of the living plant under test is cut in water, and the cut end is connected to the water container 307. Sealant stopper 308 seals the cut end and capillary transpiration to prevent leakage. By observing the movement of the liquid surface of the capillary 309 in a unit time, the total water flow Σj of all the pipes of the petiole of the plant under test is determined. Observe the number of ducts of plant petioles that have been cut with a microscope, or determine the flow velocity and total water flow of a petiole that has been cut out under a set water pressure difference, and then calculate it according to Hagen-Poiseuille's law. Number of catheters N. After the water flow and the number of plant ducts N are determined, the water flow J of a single duct can be calculated by equation (8).

The capillary transpiration meter is used to measure the total water flow of the tube by measuring the volume change of the water. Here, you can also measure the total water flow of the tube by measuring the weight change of water total water flux measurement duct, means may be utilized to sense the weight sensor sensing a change in weight of water, and then calculated the total water circulation conduit _Σ preferably according to the specific gravity of water, when using a capillary transpiration and other equipment for When measuring, directly input the total water flow measured by a capillary transpiration meter and other instruments directly into the plant water potential calculation unit 306. When measuring with a weight sensor and other instruments, the weight sensor is connected to the plant water potential calculation unit 306, and the weight sensor will measure the The total water flow Σ is transmitted to the plant water potential calculation unit 306. The calculated water flow rate of the single pipe of the plant petiole and the average water velocity of the plant pipe are input to the plant water potential calculation unit 306, and the plant water potential calculation unit 306 calculates the water pressure difference P from the formula (5), and finally calculates according to the formula (6) Plant water potential.

The above descriptions are merely preferred embodiments of the present invention, and are not intended to limit the present invention. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention shall be included in the present invention. Within the scope of protection.

Claims

Claim

1. A device for monitoring the water potential of living plants in situ, characterized in that the device comprises: a device for measuring the average flow velocity of a plant conduit, a device for measuring the water flow of a plant conduit, and a device for calculating a plant water potential, wherein:

Plant conduit average water velocity measurement device for measuring the average water velocity through a conduit of a plant material under test;

Plant conduit water flow measurement equipment for measuring the water flow through a plant material conduit;

2. The device according to claim 1, wherein the device for measuring the average water flow velocity of a plant conduit comprises: a pulse signal generating unit, a pulse signal receiving unit, and a timer, wherein:

A pulse signal generating unit for injecting a pulse signal to a first point of the plant material under test; a pulse signal receiving unit for receiving the pulse letter timer at a second point of the plant material under test; The time from when the signal is transmitted from the first point to the second point is counted;

3. The device according to claim 2, wherein the pulse signal generating unit is a thermal pulse signal generator.

4. The device according to claim 2, wherein the pulse signal generating unit is an isotope pulse signal generator.

5. The device according to claim 3, wherein the thermal pulse signal receiving device is a thermocouple temperature probe or a platinum resistance temperature probe.

6. The device according to claim 4, wherein the isotope pulse signal generator is an isotope solution injector, and the isotope emits beta rays or gamma rays.

7. The device according to claim 1, wherein the plant conduit water flow measurement device is a capillary transpiration meter, or a thermal diffusion stem flow meter, or a thermal equilibrium stem flow meter, or a plant transpiration meter, or Plant osmometer.

8. A method for monitoring the water potential of living plants in situ, characterized in that the method includes the following steps:

A. Determine the water flow of a single duct of the plant material under test J and the average water flow velocity V of the plant duct;

B. Determine the water pressure difference P according to the water flow J of the single duct of the tested plant material and the average water flow velocity V of the plant duct, where P = -8 τη ν ² Α1, π is the circumference, and η is the viscosity coefficient of water;

C. Determine the plant water potential according to the water pressure difference P.

9. The method according to claim 8, characterized in that, in step A, determining the average water flow velocity of the plant conduit is:

A12. Receive the pulse signal at the second point of the plant material under test, and record the second moment when the pulse signal is received;

10. The method according to claim 8, wherein the determining the water flow of a single plant conduit in step A is:

A22. Observe the cut cross section of the plant material to determine the number of ducts of the plant material to be tested. A23. Determine the water flux of the individual plant ducts based on the total water flow of all the ducts of the plant material to be tested and the number of ducts of the plant material to be tested.

11. The method according to claim 8, wherein the determining the water flow of a single plant duct in step A is:

A33. Determine the water flow of a single plant duct based on the total water flow of all plant ducts and the number of plant ducts tested.

12. The method according to claim 9, wherein the pulse signal is a thermal pulse signal.

13. The method according to claim 9, wherein the pulse signal is an isotope pulse signal.

14. The method according to claim 13, wherein the isotope pulse signal is an instantaneous signal of a radioisotope that emits beta rays or gamma y rays.

15. The method according to claim 8, wherein the determination of the plant water potential according to the water pressure difference P in step C is: Ψ = ^ -Π + σ, where Ψ is the plant water potential and Π is a duct solution Osmotic potential, G is the gravitational potential of the catheter fluid.

16. The method according to claim 8, wherein: The water pressure difference P determines the plant water potential as: The absolute value of the plant water potential is proportional to the absolute value of the water pressure difference.