Method and apparatus for assessing gas exchange of plants

Abstract

A method and apparatus are disclosed for assessing gas exchange of plants. The method includes receiving in a gas analyzer a plurality of test air samples from a leaf chamber corresponding respectively to first and second plant leaf samples received separately and in sequence in the leaf chamber while being exposed to light to form the first and second test air samples, the first and second test air samples being received in sequence in the gas analyzer as an integrated gas stream, and the gas analyzer analyzing the integrated gas stream as it flows therethrough. The measuring apparatus includes a leaf chamber for receiving therein a plant leaf sample to be tested, a pump communicating with the leaf chamber for supplying air thereto, and an analyzer communicating with the leaf chamber for receiving air therefrom and for analyzing the air received.

Claims

1. A method for assessing gas exchange of plants, comprising receiving in a gas analyzer a plurality of test air samples from a leaf chamber each corresponding to a respective one of a plurality of plant leaf samples received separately and in sequence in the leaf chamber while being exposed to light to form the plurality of test air samples, the plurality of test air samples being received in sequence in the gas analyzer as an integrated gas stream, and the gas analyzer analyzing the integrated gas stream as it flows therethrough.

2. The method as claimed in claim 1, further comprising receiving analysis data from the gas analyzer, processing the analysis data to produce a test result for each of the plant leaf samples, and combining the test results for the plant leaf samples to generate an average test result for the plant leaf samples.

3. The method as claimed in claim 2, wherein the analysis data received from the gas analyzer comprises a plurality of sets of signal points sequenced over time, each set of signal points corresponding to a respective test air sample of the plurality thereof.

4. The method as claimed in claim 3, wherein each of the test air samples received in the gas analyzer comprises a leading part in the flow direction, an intermediate part upstream of the leading part, and a trailing part upstream of the intermediate part, and the method comprising processing the signal points of the sets thereof which correspond to the intermediate parts of the test air samples to produce said test result for each of the plurality of plant leaf samples.

5. The method as claimed in claim 1, further comprising allowing an air flow into the leaf chamber to form the test air samples.

6. (canceled)

7. The method as claimed in claim 1, further comprising allowing reference air to flow through the leaf chamber when empty, before a first of the plurality of plant leaf samples has been received in the leaf chamber, and the gas analyzer analyzinq the reference air.

8. The method as claimed in claim 7, wherein the reference air flow is obtained from a single source of reference air, and wherein air flow into the leaf chamber to form the test air samples is also obtained from the single source of reference air.

9. The method as claimed in claim 7, wherein the reference air is unprocessed ambient air.

10. The method as claimed in claim 1, wherein said plurality of test air samples comprises at least 10 test air samples.

11. The method as claimed in claim 1, wherein each plant leaf sample is received in the leaf chamber for a period of 15 seconds or less.

12. An apparatus for assessing gas exchange of plants, comprising a leaf chamber configured to receive a plurality of plant leaf samples separately and sequentially therein and to expose the plant leaf samples to light while passing air through the leaf chamber to form a corresponding plurality of test air samples, the leaf chamber being openable for removal of one of the plurality of plant leaf samples therefrom and for receiving therein a next plant leaf sample of the plurality thereof, and a gas analyzer configured to receive from the leaf chamber the plurality of test air samples in sequence as an integrated gas stream and to analyze the integrated gas stream as it flows therethrough.

13. The apparatus as claimed in claim 12, further comprising a data processor configured to receive analysis data from the gas analyzer, to process the analysis data to produce a test result for each of the plant leaf samples, and to combine the test results for the plant leaf samples to generate an average test result for the plant leaf samples.

14. The apparatus as claimed in claim 13, wherein the gas analyzer is configured to analyze the gas stream to produce a plurality of sets of signal points sequenced over time, each set of signal points corresponding to a respective test air sample of the plurality thereof.

15. The apparatus as claimed in claim 14, wherein each of the test air samples received in the gas analyzer comprises a leading part in the flow direction, an intermediate part upstream of the leading part, and a trailing part upstream of the intermediate part, and the data processor being configured to process the signal points of the sets thereof which correspond to the intermediate parts of the test air samples to produce said test result for each of the plurality of plant leaf samples.

16. The apparatus as claimed in claim 12, further comprising a flow control valve for allowing an air flow into the leaf chamber to form the test air samples, and/or comprising a sensor for sensing when the leaf chamber is open or closed

17. (canceled)

18. The apparatus as claimed in claim 12, further comprising a pump configured to be filled with a single charge of air and sequentially to supply plural doses of air from the single charge each for passing to the leaf chamber.

19-21. (canceled)

22. A measuring apparatus for assessing gas exchange of plants, comprising a leaf chamber for receiving therein a plant leaf sample to be tested, a pump communicating with the leaf chamber for supplying air thereto, an analyzer communicating with the leaf chamber for receiving air therefrom and for analyzing the air received, wherein the pump is configured to be filled with a single charge of air and to supply plural doses of air from that single charge each for sequentially testing a respective plant leaf sample of a plurality of plant leaf samples.

23. The measuring apparatus as claimed in claim 22, wherein the pump is a bellows pump comprising a bellows and a weight for applying pressure to the bellows to discharge air.

24. The measuring apparatus as claimed in claim 22, further comprising a first one-way valve in an inlet path allowing the pump to be filled and a second one-way valve in an outlet path allowing discharge of air from the pump.

25. The measuring apparatus as claimed in claim 22, further comprising a flow control valve upstream of the leaf chamber for controlling flow of air into the leaf chamber.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Certain preferred embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, in which:

[0057] FIG. 1 is a schematic view or apparatus for assessing gas exchange of plants;

[0058] FIG. 2A is a perspective view of a pump of the apparatus;

[0059] FIG. 2B is an elevation view of the pump with its bellows in a collapsed condition;

[0060] FIG. 2C is an elevation view of the pump with the bellows in an expanded condition;

[0061] FIG. 3 is a perspective view of a leaf chamber module;

[0062] FIG. 4 is a thematic view of the leaf chamber module showing airflow into and out of the module; and

[0063] FIG. 5 is a graph showing the results of an experiment with the apparatus.

DETAILED DESCRIPTION

[0064] Referring to FIG. 1, this shows apparatus 1 for assessing gas exchange of plants, comprising a pump 2, a leaf chamber module 3, a gas analyzer 4 and a computing unit 5.

[0065] In FIG. 1, solid arrows show air flow through the system, and dotted arrows show signals sent between components of the system.

[0066] The pump has a first one-way valve 6 to which an air intake pipe 40 is connected to provide an inlet path allowing the pump to be filled. An air filter 7 is provided in the air intake pipe 40 upstream of the one-way valve 6.

[0067] The pump has an outlet path and a second one-way valve 8 in the outlet path allowing discharge of air from the pump. A first flow conduit 42 extends between the pump and the leaf chamber module 3. A flow control valve in the form of a solenoid valve 9 is provided in the first flow conduit 42 downstream of the second one-way valve 8 in order to control airflow from the pump to the leaf chamber module 3.

[0068] The leaf chamber module 3 has an inlet to allow air to flow into the module and an outlet for air to flow out of the module. A second flow conduit 43 extends between the leaf chamber module and the gas analyzer 4. A dust filter 10 is provided in the second flow conduit 43 downstream of the leaf chamber module 3 to filter air which has been exposed to a plant leaf sample. A flow meter 11 is provided in the second flow conduit 43 downstream of the dust filter and upstream of the gas analyzer 4.

[0069] The first and second conduits 42 and 43 comprise flexible pipes in this embodiment. This means that the pump 2 and the gas analyzer 4 can be carried at a spacing from the leaf chamber module 3, allowing this to be hand held and easily maneuverable while the pump and the gas analyzer can be separately carried by a user, for example in a back pack. This facilitates use in the field.

[0070] The gas analyzer 4 has an outlet path 12 for the escape of gas which has been analyzed.

[0071] The computing unit 5 consists of a system controller 13 and a data processing and logging unit 14. The system controller 13 is connected to the solenoid valve 9 so that the system controller can control the valve to switch on or off airflow as required. The leaf chamber module 3 is connected to the system controller 13 so that the leaf chamber module can send signals to the system controller to indicate whether a leaf chamber of the leaf chamber module is open or closed. This allows the system controller to control the solenoid valve 9 to switch off the airflow from the pump to the leaf chamber when the leaf chamber is open, and to switch on the airflow when the leaf chamber is closed.

[0072] The leaf chamber module 3 is connected to the data processing and logging unit 14 so that it can send signals to the unit relating to the light intensity to which a plant leaf sample is exposed and relating to the temperature of the plant leaf sample.

[0073] The flow meter 11 is connected to the system controller 13 so that it can send signals to the system controller to indicate the airflow rate from the leaf chamber module 3 to the gas analyzer 4. This can act as a check by the system controller that when the solenoid valve 9 is closed to airflow, the airflow through the flow meter 11 stops.

[0074] The gas analyzer 4 is connected to the data processing and logging unit 14 so that it can send signals to the unit 14 indicative of the concentrations of gases determined in the gas analyzer.

[0075] Further details of the pump 2 are shown in FIGS. 2A, 2B and 2C. The pump has a bellows 15 which can be expanded by a pull handle 16. This allows air to enter the bellows via the first one-way valve 6, with the air filtered by the air filter 7 upstream of the valve. The pump has a pair of vertical guide rods 17 for guiding a pressure plate 18 disposed on the bellows 15 in an up and down path. A weight 19 is located on the pressure plate 18 to cause the plate to exert pressure on the bellows, so that in use providing the solenoid valve 9 is open air flows under pressure via the second one-way valve 8 in the outlet path allowing discharge of air from the pump. The air flows through the dust filter 10 and the flow meter 11 to the gas analyzer 4.

[0076] In use, by pulling the pull handle 16 the bellows 15 is expanded and filled with a single charge of air. When the solenoid valve 9 is opened a dose of air from that single charge is delivered to the leaf chamber module 3. When the valve is closed the flow of air out of the pump and to the leaf chamber module is interrupted. The pump is configured to be filled with a single charge of air and to supply plural doses of air from single charge each for sequentially testing a respective plant leaf sample of a plurality of plant leaf samples.

[0077] The leaf chamber module 3 shown in FIG. 3 is a known type and is further shown schematically in FIG. 4. It has an inlet 24 for receiving air from the pump 2 and an outlet 25 for discharging air which has passed through a leaf chamber 21. The leaf chamber module 3 has an inlet pipe 20 to the leaf chamber 21 and an outlet pipe 22 from the leaf chamber. An operating lever 23 is provided to be hand operated to open the leaf chamber 21 for insertion of a plant leaf sample and is configured to close automatically under spring bias when the operating lever is released.

[0078] A sensor 41 is provided to sense when the leaf chamber 21 is open or closed, and is arranged to send appropriate signals to the system controller as to the open or closed status of the leaf chamber 21. This can ensure that, at least during a process of making measurements of plant leaf samples, the system controller 13 sends a signal to the solenoid valve 9 to open the valve and allow the flow of air from the pump to 2 to the inlet 24 of the leaf chamber module 3 only when the leaf chamber 21 closed.

[0079] FIG. 4 shows further details of the leaf chamber module 3. The module 3 has an upper seal 26 and a lower seal 27 which extend around the periphery of the leaf chamber 21. The leaf chamber 21 has an upper glass wall 30 and a lower glass wall 31 to assist an operator in positioning a plant leaf sample P in the leaf chamber. The leaf chamber 21 is shown in a closed condition with the plant leaf sample P gripped between the upper and lower seals such that a portion thereof extends across the leaf chamber. When the leaf chamber is opened by an operator pressing on the operating lever 23, the upper and lower seals separate to release the plant leaf sample P and allow insertion of another plant leaf sample.

[0080] A light intensity sensor 28 is provided to sense the intensity of light to which the plant leaf sample P is exposed in the leaf chamber. A leaf temperature sensor 29 is provided to sense the temperature of the plant leaf sample. Data from the light intensity sensor 28 and the leaf temperature sensor 29 is sent to the data processing and logging unit 14 in the form of signals.

[0081] A suitable gas analyzer used in the system described herein is model LI-850™ H.sub.2O/CO.sub.2 gas analyzer made by LI-COR, Inc.

[0082] Methods carried out using the apparatus of the embodiment will now be discussed.

[0083] Before starting measurements, the gravitational air pump 2 is filled by the pull handle 16 being pulled upwardly to expand the bellows 15 which then sucks ambient air into the bellows through the first one-way valve 6. For that operation, an air inlet to the air intake pipe 40 is set away from people and other potential sources of CO.sub.2/H.sub.2O. The dust filter 7 excludes from the air intake small particles that could damage the gas analyzer 4. Using the specially designed gravitational pump 2 gives several advantages over electrical gas pumps used in commercially available plant gas exchange systems: (1) it does not consume electricity, (2) it creates a constant air flow rate, i.e., avoids pulsations, (3) it collects ambient air with the same water vapor and CO.sub.2 concentrations form the immediate neighborhood of analyzed plants, and (4) one measurement in the beginning of the measurements and one in the end is enough to know reference gas concentrations. A 2 liter volume of the pump is sufficient for analysis of 50-60 plant leaf samples each for six seconds at a flow rate of 5 ml s.sup.−1. The pump may have a volume in a range of 1-3 liters, for example.

[0084] The leaf chamber 21 operates as an open system in which there is a constant air flow with a constant concentration of CO.sub.2 and water vapor through the measuring chamber. The system measures changes in the concentration of CO.sub.2 and H.sub.2O as a result of photosynthesis (decrease of CO.sub.2) and transpiration (increase of H.sub.2O) of the plant leaf sample in the chamber. Leaf temperature is measured with the sensor 29, which is preferably an infrared sensor, in the leaf chamber 21 and photosynthetically active radiation is measured with the sensor 28, which is preferably a quantum sensor. After the leaf chamber the gas is passed through the gas analyzer to measure changes in CO.sub.2 and H.sub.2O concentrations, and values are stored and processed in the data processing and logging unit 14.

[0085] By knowing the gas flow rate, leaf temperature, changes in CO.sub.2 and H.sub.2O concentrations and light; leaf rate of photosynthesis (μmol CO.sub.2 m.sup.−2 s.sup.−1), transpiration (mmol H.sub.2O m.sup.−2 s.sup.−1) and some intracellular gas exchange parameters of leaf are calculated. These parameters are key characteristics for describing plant growth speed, possible stress status and can be used to make agro technological decisions (fertilizing, watering etc).

[0086] When the flow control valve is closed air flow from the bellows of the gravitational pump 2 is prevented, whereas, when the control valve is opened air flows through the leaf chamber and the air is passed through the gas analyzer. A control unit program can judge when the leaf chamber is open and exclude from its data processing the air that came to the system as a result of diffusion, when the leaf chamber was open. Changes in gas concentrations are small, after opening and closing the leaf chamber i.e., are caused only by the analyzed leaf, and this helps the gas analyzer to stabilize and measure faster.

[0087] The basic principle of the method is to set a uniform measurement time for collecting gas exchange data from a single plant leaf sample and to pool gas exchange values of several samples in the same plot of land within a short timeframe. The measurement time for collecting data from one plant leaf sample and number of samples for which data will be pooled can be adjusted by the experimenter. A minimal time for getting reliable values from one leaf is 5 seconds and a practical number of leaves measured within one measurement cycle is 20-50 leaves.

[0088] In the beginning of each measurement cycle air from the pump 2 is measured to get the reference CO.sub.2 and H.sub.2O values, and after that measurements with plant leaves can start. As an example, in several tests in field conditions the exposure time of one plant leaf sample was set to 6 seconds and then it took approximately 6 minutes to measure photosynthesis and transpiration of 20 wheat leaves growing in a 2×5 m plot and measurement of 10 plots took an hour.

[0089] An example of a method for assessing gas exchange of plants will be described with reference to FIG. 5.

[0090] Initially, the leaf chamber 21 is closed and reference air from the pump is passed through the leaf chamber and to the gas analyzer 4, by virtue of the weight 19 exerting downward pressure on the bellows 15 providing a pumping pressure and the flow of reference air. The gas analyzer sends signals to the data processing and logging unit 14 which calculates the reference concentrations of CO.sub.2 and H.sub.2O, and stores that information.

[0091] The airflow from the pump 2 is stopped and the air pressure in the bellows 15 resists the downward pressure created by the weight 19. The leaf chamber 21 is opened and a first plant leaf sample is received therein. In this embodiment, a leaf is clamped between the seals around the periphery of the leaf chamber, so that a portion of the leaf forms the first plant leaf sample in the leaf chamber. Once the plant leaf sample is in position the leaf chamber is closed, and in response the leaf chamber module 3 sends a signal to the system controller 13, which in turn sends a signal to the solenoid valve 9 to open the valve. Air flow from the pump resumes and this continues for a predetermined testing period, in this case seven seconds. At the end of the predetermined period the system controller 13 sends a signal to the solenoid valve 9 to close the valve.

[0092] An indication is provided to the operator of the leaf chamber module 3 that the testing period for the sample is complete, so that the leaf chamber is then opened by the operator. The first plant leaf sample is removed and a second plant leaf sample is inserted in the leaf chamber. The operator closes the leaf chamber, and again the leaf chamber module 3 sends a signal to the system controller 13, which in turn sends a signal to the solenoid valve 9 to open the valve. Airflow from the pump again resumes and this continues for the same predetermined testing period, until the system controller 13 sends a signal to the solenoid valve 9 and the valve is closed.

[0093] During the period when the leaf chamber 21 is open for removal of the first plant leaf sample and insertion of the second plant leaf sample there is no airflow from the pump and so the air between the solenoid 9 and the leaf chamber, the air in the leaf chamber, and the air in the flow conduit 43 between the leaf chamber and the gas analyzer, is generally static. Some diffusion takes place between the inside of the leaf chamber and the surrounding ambient atmosphere. Once the leaf chamber is closed again the air captured therein is a mixture of air affected by the first plant leaf sample and ambient air. With the resumption of airflow through the system, this mixed air later reaches the gas analyzer.

[0094] The exposure of the first plant leaf sample to light in the leaf chamber during the first predetermined test period (seven seconds in this example) generates a first test air sample. This flows out of the leaf chamber with a leading part in the flow direction, an intermediate part upstream of the leading part, and a trailing part upstream of the intermediate part. Upstream of this there is the mixture of air described above. As flow continues along the flow conduit 43 out of the leaf chamber 21 and towards the gas analyzer 4, the mixture is followed by a second test air sample generated by the second plant leaf sample. The second test air sample also has a leading part in the flow direction, an intermediate part upstream of the leading part, and a trailing part upstream of the intermediate part.

[0095] The first and second test air samples form an integrated gas stream, in that they flow together in a row and at the same rate, including if the flow stops, such as for example when the leaf chamber is opened. Thus, the integrated gas stream flows or stops in an integrated manner. This is similar to the carriages of a train, which move together or stop in unison. The first and second test air samples flow in parallel and one after the other into the gas analyzer from the leaf chamber.

[0096] As described in relation to this embodiment, the integrated gas stream also includes an air mixture corresponding to the time when the leaf chamber is open. When the integrated gas stream stops flowing, for example at a time when the leaf chamber is opened to remove the second plant leaf sample and insert a third plant leaf sample, the first and second test air samples stop together with the air mixture upstream of the first test air sample and downstream of the second test air sample.

[0097] FIG. 5 is a graph showing signal points representing the concentration of CO.sub.2 at timewise spaced measuring points, as measured by the gas analyzer and sent as signals to the processing and logging unit 14. The graph shows the concentrations measured for second, third and fourth plant leaf samples, as indicated. In this example, each plant leaf sample was exposed for a testing period of seven seconds, and each test air sample generated by the exposure flowed along the flow conduit to the gas analyzer.

[0098] The signal data points each correspond to a measurement taken over 0.5 seconds, so that there are 14 signal data points for each plant leaf sample for the seven second test. The graph shows signal data points as hollow squares and filled in squares. Considering the second test air sample, indicated as “Second test air sample” in the graph, this has a leading part 51 consisting of two filled in squares, an intermediate part 52 consisting of 10 hollow squares, and a trailing part 53 consisting of two filled in squares.

[0099] The signal data points of the intermediate part are used by the data processing and logging unit 14 to determine the CO.sub.2 concentration measured for the second plant leaf sample. This is because the leading part 51 is adjacent to mixed air in the flow conduit 43 from the leaf chamber to the gas analyzer, corresponding to the time when the chamber was opened to remove the first plant leaf sample and insert the second plant leaf sample. During this open time ambient air diffuses into the leaf chamber, so that when the chamber is closed again it contains a mixture of air from the first plant leaf sample test and ambient air. By using the intermediate part 52 of the second test air sample, gas concentrations in the leading part 51 influenced by the mixture of air between the first and second test air samples are disregarded. Similarly, by using the intermediate part 52 of the second test air sample, gas concentrations in the trailing part 53 influenced by the mixture of air between the second and third test air samples are disregarded.

[0100] The signal data points of the leading part 51 and the trailing part 53 of the second test sample are disregarded by the data processing and logging unit 14. The same applies to the other test air samples.

[0101] The graph in FIG. 5 shows the signal points as measured in the gas analyzer as the air flows therethrough. It will be seen from the upper region of the graph that whilst the second test air sample flows through the gas analyzer, the third plant leaf sample is being exposed in the leaf chamber to air from the pump. The same applies to the other test air samples and plant leaf sample exposures.

[0102] The graph shows the results for measuring CO.sub.2 and similar measurements are carried out for H.sub.2O.

[0103] In the experiment the results of which are shown in FIG. 5, it will be seen that each plant leaf sample had different levels of photosynthesis. The fourth plant leaf sample had the highest photosynthesis, producing signal points with the lowest CO.sub.2 concentrations, and the third plant leaf sample had the smallest photosynthesis. The first and second plant leaf samples had approximately the same photosynthesis as each other.

[0104] The data processing and logging unit 14 receives the signal points for the gas concentrations from the gas analyzer. Previously, signal points for the gas concentrations from the reference air were measured by the gas analyzer, passed to the data processing and logging unit 14, and stored in a memory thereof. The data processing and logging unit 14 calculates the change in CO.sub.2 and H.sub.2O gas concentrations compared to the concentrations of those gases in the reference air. These changes represent the photosynthesis (decrease in CO.sub.2) and transpiration (increase in H.sub.2O) activity of each plant leaf sample. Based on the gas concentration measurements of plural plant leaf samples, the data processing and logging unit 14 calculates average values for photosynthetic activity and water transpiration. The data processing and logging unit 14 generates a combined gas exchange analysis for the plural leaf samples, this analysis being derived from the sets of signal points produced by the gas analyzer for the plural plant leaf samples.

[0105] Such a measurement procedure makes it possible to analyze a large number of leaves in a relatively short timeframe and gives the average values for photosynthetic activity and water transpiration, which quite correctly reflects the physiological status of plants in the community. Moreover, short exposures (5-6 seconds) provides this data corresponding to the real situation in the field, since during this time the “chamber effect” is minimal. No other commercially available gas exchange system allows such speed in gas exchange data collection.

[0106] The apparatus and method of the embodiment allow assessment of the physiological status of plant communities in the field and this information can be used in agro technological decision-making processes or for selecting plant lines with improved photosynthetic production and efficient water-use.

[0107] It will be seen that in this specification there is described a novel scheme for obtaining gasometric data from plant leaf samples. The apparatus and applied methodology are based on fast measurements of photosynthesis and transpiration of a large number of leaves according to a principle of “many samples—one measurement”. Such a method is revolutionary and allows the measurement of the physiological parameters of entire plant communities. The principle of this method involves integration of the measured samples by summing up individual short measurements. Such a measurement principle allows the analysis of one plant leaf sample within a very short exposure time and enables the collection of data from a large number of leaves within a few minutes.

[0108] Considering the daily dynamics of the environment, as well as the complex structure of plant communities in the field, the system of the embodiments described herein is advantageous because it can provide gas exchange data for several hundreds of leaves in one day. The portable apparatus enables in situ measurements of photosynthesis of plural plant leaf samples, for example hundreds of leaves, under natural dynamic field conditions and at different layers within the canopy is required.