Method for estimating photosynthetic nitrogen content of rice leaves based on sunlight-induced chlorophyll fluorescence

Abstract

The invention provides a method for estimating the photosynthetic nitrogen content of rice leaves based on sunlight-induced chlorophyll fluorescence. The method comprises the following steps: acquiring an observed value SIF of canopy sunlight-induced chlorophyll fluorescence based on induction equipment, and converting the observed value SIF into a total fluorescence excitation value SIFPSII of a light system II; on the basis of the rice photosynthetic physiological process, the incident photosynthetically active radiation I and the total fluorescence excitation value SIFPSII of a light system II, the electron transmission rate J is obtained through calculation, and the maximum electron transmission rate Jmax is obtained through calculation; then, the maximum carboxylation rate Vcmax is calculated based on the electron transmission rate J, so that the photosynthetic nitrogen content Ncb distributed to a carboxylation system and the photosynthetic nitrogen content Net distributed to an electron transmission system are calculated respectively, and the photosynthetic nitrogen content Ncb and the photosynthetic nitrogen content Net are superposed to obtain an estimated value PN of the photosynthetic nitrogen content of the leaves. According to the method, accurate estimation of the photosynthetic nitrogen content of the rice leaves is realized based on the mechanism relation between sunlight-induced chlorophyll fluorescence and the photosynthesis process of the rice, and accurate estimation of the photosynthetic nitrogen content of the rice in the field and regional scale can be realized.

Description

Technical Field

[0001] The present application relates to the field of smart agricultural technology, and more specifically to a high-precision estimation technology for the photosynthetic nitrogen content of rice leaves. Background Art

[0002] Nitrogen is an important nutrient for rice growth, and leaf nitrogen content has a significant effect on rice photosynthesis. As one of the most important leaf functional traits, leaf nitrogen content has a significant impact on rice photosynthesis by affecting the necessary substances for the photosynthetic process (Rubisco enzyme, etc.). At present, there is still great uncertainty in the prediction results of rice yield at the field and regional scales. One important reason is that the actual distribution process of nitrogen in rice leaves is not taken into account, especially the distribution of nitrogen that affects the photosynthetic capacity of rice leaves. The reason is that what really affects the photosynthetic capacity of rice leaves is the nitrogen allocated to the photosynthetic part (that is, the photosynthetic nitrogen content of the leaves). Leaf photosynthetic nitrogen mainly includes the carboxylation system (N cb ) and electron transport components (N et ) The nitrogen allocation ratio of the photosynthetic system determines the photosynthetic capacity of crops. The higher the ratio, the more conducive it is to the carbon assimilation efficiency of crops. Therefore, how to more accurately estimate the photosynthetic nitrogen content of rice leaves has become an important support for accurately quantifying and predicting rice photosynthesis and yield.

[0003] At present, it is not possible to accurately extract the photosynthetic nitrogen content of leaves based on chemical methods. At present, most crop models estimate the key parameters of rice photosynthesis through leaf nitrogen content, but the estimation results of this method are weakly correlated with the observed data because the actual distribution process of nitrogen in rice leaves is not considered. What really affects the photosynthetic capacity of rice leaves is the nitrogen element allocated to the photosynthetic part (that is, the photosynthetic nitrogen content of the leaves). The resulting differences in the estimation of photosynthetic parameters are one of the main sources of uncertainty in the simulation results of crop models.

[0004] Under the existing technology, photosynthetic instruments such as photosynthetic meters are used in the field to measure the physiological parameters of leaves (such as the maximum carboxylation rate V cmax and the maximum electron transfer rate J max The main method currently used is to indirectly estimate the photosynthetic nitrogen content of leaves by observing the nitrogen content of leaves at the field level. However, due to the variable field environmental conditions and limited instrument accuracy, the observation error of this method is very large. In addition, this method can only be used for single-point field observations, and it is difficult to accurately estimate the photosynthetic nitrogen content of leaves at the field and regional scales. The estimation results are highly uncertain and time-consuming and labor-intensive. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention provides a method for estimating the photosynthetic nitrogen content of rice leaves based on sunlight-induced chlorophyll fluorescence (SIF) and V cmax and J max The mechanism of V cmax、 J max The connection between the carboxylation system nitrogen component and the electron transfer nitrogen component is calculated on this basis, and the photosynthetic nitrogen content components allocated to the electron transfer system and the carboxylation system are calculated respectively. The total value of the photosynthetic nitrogen content of the rice leaves is obtained by adding the two together, and a more accurate estimation result of the photosynthetic nitrogen content of the leaves is obtained. The present application specifically adopts the following technical scheme.

[0006] First, in order to achieve the above purpose, a method for estimating the photosynthetic nitrogen content of rice leaves based on sunlight-induced chlorophyll fluorescence is proposed, which is characterized by the following steps: the first step is to obtain the observed value SIF of canopy sunlight-induced chlorophyll fluorescence, and convert it into the fluorescence excitation value SIF of photosystem II. PSII ; The second step is to convert the fluorescence excitation value SIF of photosystem II into the fluorescence excitation value SIF of photosystem II based on the photosynthetic physiological process of rice and the incident photosynthetic active radiation I. PSII Convert to electron transfer rate J and estimate the maximum electron transfer rate J max ; The third step is to calculate the maximum carboxylation rate V based on the principle of evolutionary optimality through the electron transfer rate J cmax ; Step 4, based on the above maximum electron transfer rate J max and the maximum carboxylation rate V cmax Calculate the photosynthetic nitrogen content N allocated to the carboxylation system cb and the photosynthetic nitrogen content of the electron transport system et , and superimpose the two to obtain the estimated value of leaf photosynthetic nitrogen content PN: .

[0007] Optionally, in any of the above methods for estimating photosynthetic nitrogen content of rice leaves based on sunlight-induced chlorophyll fluorescence, in the first step, the observed value SIF of canopy sunlight-induced chlorophyll fluorescence is converted into the fluorescence excitation value SIF of photosystem II. PSII The specific steps include: based on the photosynthetic physiological process of rice, first calculate the ratio of the fluorescence excitation value of photosystem II to the canopy fluorescence observation value. ; Multiplying this ratio by the observed value of canopy sunlight-induced chlorophyll fluorescence SIF gives the fluorescence excitation value of photosystem II: ; where m1 and m2 are 0.00561 and 0.00917 respectively; ε is the fluorescence yield in photosystem II under steady-state conditions ( F) and minimum fluorescence yield ( F0), F is obtained through field observation. The F0 value is 0.02.

[0008] Optionally, in any of the above methods for estimating photosynthetic nitrogen content in rice leaves based on sunlight-induced chlorophyll fluorescence, in the second step, the fluorescence excitation value SIF of photosystem II is converted to PSII The specific steps for converting to the electron transfer rate J include:

[0009] :

[0010]

[0011]

[0012]

[0013] calculate and , and then the estimated value of the electron transfer rate J is calculated to be ;

[0014] The maximum electron transfer rate was calculated based on the estimated value of the electron transfer rate J. ;

[0015] Among them, qL is the open ratio of photosystem II, which is obtained by observing the active fluorescence instrument in the field; is equal to 0.257, I is the incident photosynthetically active radiation, is the curvature of the light response curve ( =0.85); rNIR, rRED, and RE are the reflectances of the near-infrared band, infrared band, and red-edge band, respectively.

[0016] Optionally, in any of the above methods for estimating photosynthetic nitrogen content of rice leaves based on sunlight-induced chlorophyll fluorescence, in the third step, based on the optimality principle of evolution theory, the following is obtained:

[0017] ;

[0018] Then, the maximum electron transfer rate J is calculated max The corresponding maximum carboxylation rate is ;

[0019] In the formula, A c and A j are the photosynthesis rates limited by carboxylation rate and electron transport rate, m and m c is the parameter calculated by the above formula; C a is the atmospheric CO2 concentration, which is obtained from meteorological observation data; X is the ratio of intercellular and atmospheric CO2 concentrations, which is 0.7; is the CO2 compensation point, usually 6Pa; K m It is a constant whose value is 129.

[0020] Optionally, in any of the above methods for estimating photosynthetic nitrogen content of rice leaves based on sunlight-induced chlorophyll fluorescence, in the fourth step, based on the maximum carboxylation rate V cmax The photosynthetic nitrogen content allocated to the carboxylation system is calculated as , where V cr It represents the CO2 carboxylation activity of Rubisco enzyme at 25℃, and its value is 20.78μmol .

[0021] Optionally, in any of the above methods for estimating photosynthetic nitrogen content in rice leaves based on sunlight-induced chlorophyll fluorescence, in the fourth step, based on the maximum electron transfer rate J max The photosynthetic nitrogen content allocated to the electron transport system is calculated as , where J mc It represents the number of electrons transferred by cytochrome per second at 25°C, and its value is 155.65 μmol electrons .

[0022] Optionally, a method for estimating the photosynthetic nitrogen content of rice leaves based on sunlight-induced chlorophyll fluorescence as described above, wherein the reflectances rNIR, rRED, RE of the near-infrared band, infrared band and red-edge band are respectively collected by a field multi-spectrometer or a multi-spectrometer carried by an unmanned aerial vehicle, and specific values ​​are obtained by calibrating the multi-spectral data collected at the field or regional scale.

[0023] At the same time, to achieve the above purpose, the present application also provides an application of the aforementioned method, including: re-observing the open ratio (qL) of photosystem II according to the crop type, keeping other steps unchanged, for estimating the photosynthetic nitrogen content of the crop leaves.

[0024] Beneficial Effects

[0025] The present application provides a method for estimating the photosynthetic nitrogen content of rice leaves based on sunlight-induced chlorophyll fluorescence. The present application is based on the observation value SIF of canopy sunlight-induced chlorophyll fluorescence acquired by the sensing device, which is first converted into the fluorescence excitation value SIF of photosystem II. PSII Based on the photosynthetic physiological process of rice and incident photosynthetically active radiation I, the fluorescence excitation value SIF of photosystem II PSIIThe electron transfer rate J is calculated, and the maximum electron transfer rate Jmax is calculated; finally, the maximum carboxylation rate Vcmax is calculated based on the electron transfer rate J, so as to calculate the photosynthetic nitrogen content Ncb allocated to the carboxylation system and the photosynthetic nitrogen content Net of the electron transfer system respectively, and the two are superimposed to obtain the estimated value PN of the photosynthetic nitrogen content of the leaves. The present invention relies on the mechanism connection between sunlight-induced chlorophyll fluorescence and the photosynthesis process of rice to achieve accurate estimation of the photosynthetic nitrogen content of rice leaves, and can achieve accurate estimation of the photosynthetic nitrogen content of rice at field and regional scales.

[0026] Other features and advantages of the present application will be set forth in the following description, and in part will become apparent from the description, or may be understood by practicing the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings are used to provide a further understanding of the present application and constitute a part of the specification. Together with the embodiments of the present application, they are used to explain the present application and do not constitute a limitation of the present application. In the accompanying drawings:

[0028] Figure 1 It is a schematic flow chart of the steps of the method for estimating leaf photosynthetic nitrogen allocation based on SIF provided in this application.

[0029] Figure 2 The J calculation results based on the present invention (line graph), where the X-axis is different treatments, and the Y-axis is J and SIF PSII a and b are the results from two different years.

[0030] Figure 3 V based on the present invention cmax Calculation results (line graph), where the X-axis is different treatments and the Y-axis is V cmax With SIF PSII a and b are the results from two different years.

[0031] Figure 4 The calculation results of leaf photosynthetic nitrogen content based on the traditional method (scatter plot), where the X-axis is the observed leaf photosynthetic nitrogen content, the Y-axis is the leaf photosynthetic nitrogen content estimated based on the traditional method, and the straight line in the figure represents the linear fitting relationship between the estimated photosynthetic nitrogen content and the observed photosynthetic nitrogen content.

[0032] Figure 5 It is the calculation result of leaf photosynthetic nitrogen content based on the method of the present invention (scatter plot), wherein the X-axis is the observed leaf photosynthetic nitrogen content, the Y-axis is the leaf photosynthetic nitrogen content estimated based on the method of the present invention, and the straight line in the figure represents the linear fitting relationship between the estimated photosynthetic nitrogen content and the observed photosynthetic nitrogen content. DETAILED DESCRIPTION

[0033] In order to make the purpose and technical solution of the embodiment of the present application clearer, the technical solution of the embodiment of the present application will be clearly and completely described in conjunction with the drawings of the embodiment of the present application. Obviously, the described embodiment is a part of the embodiment of the present application, not all of the embodiments. Based on the described embodiment of the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0034] It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as generally understood by those skilled in the art to which this application belongs. It should also be understood that terms such as those defined in common dictionaries should be understood to have meanings consistent with the meanings in the context of the prior art, and will not be interpreted with idealized or overly formal meanings unless defined as herein.

[0035] Currently, the estimation of nitrogen content in rice leaves mainly uses methods such as field sampling, which is unable to separate the photosynthetic and non-photosynthetic parts of the leaf nitrogen distribution process, resulting in great uncertainty in the prediction results of rice yield at field and regional scales.

[0036] In order to overcome the inaccuracy of photosynthetic nitrogen calculation in the prior art, the present application provides a method based on sunlight-induced chlorophyll fluorescence (SIF) and V cmax and J max This application is based on the nitrogen distribution of photosynthetic components in rice leaves (nitrogen distribution in the carboxylation system and nitrogen distribution in the electron transfer system), and can be widely used in fields and regional scales to achieve high-precision estimation of photosynthetic nitrogen content in rice leaves based on SIF and mechanism processes.

[0037] Specifically, based on the photosynthetic physiological process of rice, the SIF observation value at the canopy scale is converted into the total fluorescence excitation value (SIF) of photosystem II. PSII On this basis, relying on the mechanistic relationship between SIF and electron transfer rate and maximum carboxylation rate, and according to the photosynthetic physiological process of rice, SIF was constructed. PSII and electron transfer rate (J) and V cmax The mechanistic connection between them realizes the nitrogen distribution of rice leaves, that is, rice leaves J max and V cmax On this basis, the photosynthetic nitrogen content components allocated to the electron transfer system and the carboxylation system were further calculated, and the two were added together to obtain the total value of the photosynthetic nitrogen content of rice leaves.

[0038] In order to solve the problem of how to quantitatively calculate V in the above rice photosynthetic nitrogen allocation estimation method cmax and Jmax The core issue of this application can be specifically adopted Figure 1 The following scheme is shown:

[0039] First, the SIF data are inverted based on the hyperspectral instrument of satellite, UAV or near-ground platform to obtain the observation value SIF of canopy sunlight-induced chlorophyll fluorescence, and the SIF observation value at the canopy scale is converted into the total fluorescence excitation value of photosystem II (SIF PSII );

[0040] Then, based on SIF PSII The electron transfer rate (J) and the maximum carboxylation rate (V cmax ) is based on the photosynthetic physiological process of rice and the incident photosynthetically active radiation I, and the fluorescence excitation value SIF of photosystem II is converted to PSII Convert to electron transfer rate J and estimate the maximum electron transfer rate J max , and then based on the optimality principle of evolution, calculate the maximum electron transfer rate J max The corresponding maximum carboxylation rate V cmax . Achieving the maximum electron transfer rate in rice leaves (J max ) and the maximum carboxylation rate (V cmax ) to accurately estimate;

[0041] Finally, based on this, the maximum electron transfer rate J max and the maximum carboxylation rate V cmax Calculate the content of photosynthetic nitrogen components allocated to the electron transport system and the carboxylation system, and convert the photosynthetic nitrogen content N allocated to the carboxylation system cb and the photosynthetic nitrogen content of the electron transport system et The estimated value of leaf photosynthetic nitrogen content PN is obtained by accumulating , and the estimation accuracy of this method is verified.

[0042] The detailed construction and calculation process of the above model are described as follows:

[0043] 1) Based on the hyperspectral observation data in the near-infrared band, the sunlight-induced chlorophyll fluorescence (SIF) observation values ​​of rice leaves were inverted and then converted into the fluorescence excitation value of photosystem II (SIF PSII );

[0044] Based on the photosynthetic physiological process of rice, the fluorescence excitation process of rice leaves will be generated in both photosystem I and photosystem II, and only the fluorescence value of photosystem II is closely related to the electron transfer rate. Therefore, this method only focuses on the fluorescence excitation value of photosystem II. First, calculate the ratio of the fluorescence excitation value of photosystem II to the canopy fluorescence observation value (fpsII), and the formula is as follows:

[0045]

[0046] Where fpsII is the ratio of the fluorescence excitation value of photosystem II to the canopy fluorescence observation value, m1 and m2 are 0.00561 and 0.00917 respectively; ε is the fluorescence yield in photosystem II under steady-state conditions ( F) and minimum fluorescence yield ( F0), F can be obtained through field observation. F0 is usually taken as 0.02.

[0047] On this basis, the total fluorescence excitation value of photosystem II (SIF) can be obtained by multiplying this ratio with the value of canopy sunlight-induced chlorophyll fluorescence. PSII ):

[0048]

[0049] 2) Based on the mechanism of photosynthesis and field observation data verification, the total fluorescence excitation value (SIF) of photosystem II was derived. PSII ) and the electron transfer rate (J), and an accurate estimate of J can be achieved, namely:

[0050] ,

[0051] in,

[0052]

[0053]

[0054] In the formula, SIF PSII is the fluorescence excitation value of photosystem II; qL is the open ratio of photosystem II, which can be observed by field active fluorescence instruments. rNIR, rRED, and RE are the reflectances of the near-infrared band, infrared band, and red-edge band, respectively. Multispectral data can be collected at the field or regional scale by field multispectrometers or multispectrometers carried by drones, and then the obtained data can be calibrated to obtain the specific values ​​of rNIR, rRED, and RE.

[0055] On this basis, according to the relationship between J and the maximum electron transfer rate (J max ) between the two mechanisms, max Make an estimate:

[0056] ,

[0057] in, is equal to 0.257, I is the incident photosynthetically active radiation, is the curvature of the light response curve ( =0.85).

[0058] 3) Based on the optimality principle of evolution, we can get:

[0059]

[0060] In the formula, A c and A j are the photosynthesis rates limited by carboxylation rate and electron transport rate, m and m c is the parameter; C a is the atmospheric CO2 concentration, which can be obtained from meteorological observation data; X is the ratio of intercellular and atmospheric CO2 concentrations (about 0.7); is the CO2 compensation point, usually 6Pa; K m is a constant (approximately 129). According to the above formula, V cmax :

[0061]

[0062] 4) Calculate the photosynthetic nitrogen components allocated to the electron transport system and the carboxylation system respectively, and add the two together to obtain the total value of photosynthetic nitrogen content in rice leaves;

[0063] Based on the above electron transfer rate and maximum carboxylation rate, the photosynthetic nitrogen content N allocated to the electron transfer system was calculated. et and photosynthetic nitrogen content of the carboxylation system cb , and finally achieve accurate estimation of rice leaf photosynthetic nitrogen content (PN), the specific calculation formula is as follows:

[0064]

[0065]

[0066]

[0067] Where V cr It represents the CO2 carboxylation activity of Rubisco enzyme at 25℃, and its value is 20.78μmol , J mc It represents the number of electrons transferred by cytochrome per second at 25°C, and its value is 155.65 μmol electrons .

[0068] The calculation results of the traditional method are compared with the calculation results of the method provided by the present invention.

[0069] Based on the traditional method and the method of the present invention, the estimated results of photosynthetic nitrogen content in rice leaves were obtained, and the accuracy was compared. The square of the correlation coefficient (R 2 ), mean absolute error (MAE), and root mean square error (RMSE) can be compared as the evaluation criteria to obtain the following table:

[0070] Table 1 Comparison of the accuracy of the calculation results of the traditional method and the calculation results of the method of the present invention

[0071] It can be seen from Table (1) that, compared with the calculation results of the traditional method, the method of the present invention can greatly improve the estimation accuracy of the photosynthetic nitrogen content of rice leaves, and its root mean square error is improved by 35.59% compared with the traditional method.

[0072] In summary, this application achieves high-precision estimation of nitrogen distribution of photosynthetic components of rice leaves (nitrogen distribution of carboxylation system and nitrogen distribution of electron transfer system) based on SIF observation. Compared with the traditional linear model method, the new method of the present invention can effectively improve the estimation accuracy of nitrogen distribution of carboxylation system and nitrogen distribution of electron transfer system, and can provide basic support for accurate quantification and prediction of rice photosynthesis and yield.

[0073] The present invention firstly transforms the canopy-scale sunlight-induced chlorophyll fluorescence (SIF) observation value into the total fluorescence excitation value (SIF) of photosystem II based on the photosynthetic physiological process of rice. PSII ); Secondly, based on the total fluorescence excitation value of photosystem II (SIF PSII ) and the electron transfer rate (J), achieving J and the maximum electron transfer rate (J max ) and then combine J with the maximum carboxylation rate V cmax The mechanism of V cmax Make an estimate; finally, based on the J calculated above max and V cmax , calculate the photosynthetic nitrogen components allocated to the electron transfer system and the carboxylation system respectively, and add the two together to obtain the total value of the photosynthetic nitrogen content of rice leaves. The present invention relies on the mechanistic connection between sunlight-induced chlorophyll fluorescence and the rice photosynthesis process to achieve accurate estimation of the photosynthetic nitrogen content of rice leaves, which can provide a new method for estimating the photosynthetic nitrogen content of rice at the field and regional scales.

[0074] In addition, the method is not only applicable to the estimation of photosynthetic nitrogen content of rice leaves, but also can be used to estimate the photosynthetic nitrogen content of leaves of other crops by re-observing the open ratio (qL) of photosystem II according to the crop type. The other steps of the estimation are all consistent with the above embodiment, and only the open ratio (qL) of the corresponding photosystem II is updated.

[0075] The above is only an implementation method of the present application, and its description is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present application. It should be pointed out that for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present application, which all belong to the protection scope of the present application.

Claims

1. A method for estimating photosynthetic nitrogen content of rice leaves based on sunlight-induced chlorophyll fluorescence, characterized in that the steps include: The first step is to obtain the observed value SIF of canopy sunlight-induced chlorophyll fluorescence and convert it into the fluorescence excitation value SIF of photosystem II PSII ; The second step is to convert the fluorescence excitation value SIF of photosystem II into the fluorescence intensity of the photosystem II based on the photosynthetic physiological process of rice and the incident photosynthetically active radiation I. PSII Convert to electron transfer rate J and estimate the maximum electron transfer rate J max ; The third step is to calculate the maximum carboxylation rate V based on the principle of evolutionary optimality through the electron transfer rate J. cmax ; The fourth step is based on the maximum electron transfer rate J max and the maximum carboxylation rate V cmax Calculate the photosynthetic nitrogen content N allocated to the carboxylation system cb and the photosynthetic nitrogen content of the electron transport system et The estimated value of leaf photosynthetic nitrogen content PN is obtained by superimposing the two as PN = N cb +N et .

2. The method for estimating photosynthetic nitrogen content of rice leaves based on sunlight-induced chlorophyll fluorescence according to claim 1, characterized in that: In the first step, the observed value of canopy sunlight-induced chlorophyll fluorescence (SIF) is converted into the fluorescence excitation value of photosystem II (SIF). PSII The specific steps include: Based on the photosynthetic physiological process of rice, the ratio of the fluorescence excitation value of photosystem II to the canopy fluorescence observation value is first calculated as follows: Multiplying this ratio by the observed value of canopy sunlight-induced chlorophyll fluorescence SIF gives the fluorescence excitation value of photosystem II: SIF PSII =f psII ·SIF; Among them, m1 and m2 are 0.00561 and 0.00917 respectively; ε is the ratio of the fluorescence yield (φF) in photosystem II under steady-state conditions to the minimum fluorescence yield (φF0), φF is obtained through field observations, and φF0 is taken as 0.

02.

3. The method for estimating photosynthetic nitrogen content of rice leaves based on sunlight-induced chlorophyll fluorescence according to claim 1, characterized in that: In the second step, the fluorescence excitation value SIF of photosystem II is PSII The specific steps for converting to the electron transfer rate J include: fPAR=1.37×NDVI rededge -0.17: NDVI rededge =(rNIR-RE) / (rNIR+RE) NIRv=NDVI×rNIR NDVI=(rNIR-rRED) / (rNIR+rRED) Calculate NIRv and fPAR, and then calculate the estimated value of the electron transport rate J as The maximum electron transfer rate was calculated based on the estimated value of the electron transfer rate J. Among them, qL is the open ratio of photosystem II, which is obtained by observing the active fluorescence instrument in the field; is equal to 0.257, I is the incident photosynthetically active radiation, θ is the curvature of the light response curve (θ=0.85); rNIR, rRED, and RE are the reflectances of the near-infrared band, infrared band, and red-edge band, respectively.

4. The method for estimating photosynthetic nitrogen content of rice leaves based on sunlight-induced chlorophyll fluorescence according to claim 1, characterized in that: In the third step, based on the optimality principle of evolution, we get: Then, the maximum electron transfer rate J is calculated max The corresponding maximum carboxylation rate is In the formula, A c and A j are the photosynthesis rates limited by carboxylation rate and electron transport rate, m and m c is the parameter calculated by the above formula; C a is the atmospheric CO2 concentration, which is obtained from meteorological observation data; X is the ratio of the intercellular and atmospheric CO2 concentrations, which is 0.7; Γ - is the CO2 compensation point, usually 6Pa; K m It is a constant whose value is 129.

5. The method for estimating photosynthetic nitrogen content of rice leaves based on sunlight-induced chlorophyll fluorescence according to claim 1, characterized in that: In the fourth step, based on the maximum carboxylation rate V cmax The photosynthetic nitrogen content allocated to the carboxylation system is calculated as Among them, V cr It represents the CO2 carboxylation activity of Rubisco enzyme at 25℃, and its value is 20.78μmolCO2(gRubisco) -1 s -1 .

6. The method for estimating photosynthetic nitrogen content of rice leaves based on sunlight-induced chlorophyll fluorescence according to claim 1, characterized in that: In the fourth step, based on the maximum electron transfer rate J max The photosynthetic nitrogen content allocated to the electron transport system is calculated as Among them, J mc Indicates the number of electrons transferred by cytochrome per second at 25°C, and its value is 155.65 μmol electrons (μmol Cyt f) -1 s -1 .

7. The method for estimating photosynthetic nitrogen content of rice leaves based on sunlight-induced chlorophyll fluorescence according to claim 3, characterized in that: The reflectances rNIR, rRED and RE of the near-infrared band, infrared band and red-edge band are respectively collected by a field multi-spectrometer or a multi-spectrometer carried by an unmanned aerial vehicle. The specific values ​​are obtained by calibrating the multi-spectral data collected at the field or regional scale.

8. The use of the method according to any one of claims 1 to 7, characterized in that: The open proportion of photosystem II (qL) was re-observed according to the crop type, and other steps were kept unchanged to estimate the photosynthetic nitrogen content of the leaves of the crop.

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