Method for monitoring net primary productivity of mangrove plant community based on trunk flow

Abstract

The invention discloses a mangrove plant community net primary productivity monitoring method based on trunk flow, and relates to ecology and botany. General regulations of mangrove plant community net primary productivity monitoring based on trunk stem flow, mangrove plant stem flow monitoring content and method, plant leaf and crown atmospheric stability isotope monitoring, mangrove plant community net primary productivity calculation method and other basic contents and requirements are given. The method comprises the following steps: monitoring the stem flow density of a sample tree by adopting a plant stem liquid flow monitoring system, obtaining the composition condition of plant leaf juice and 13C in the canopy atmosphere by adopting an isotope analyzer, and obtaining the canopy leaf area index by adopting a fisheye lens and related software; and calculating the real-time net primary productivity of the mangrove plant community according to the monitored data. The method can be applied to monitoring of net primary productivity of various mangrove forests or land forests. The method is accurate in monitoring, high in popularization degree and good in real-time performance, and solves the problems of poor continuity, high operation difficulty and the like in current mangrove plant community net primary productivity measurement and calculation.

Description

Technical Field

[0001] The present invention relates to the fields of ecology and botany, particularly to the carbon fixation ability during the growth process of plants, specifically to a method for monitoring the net primary productivity of a mangrove plant community based on stem flow, which is used for monitoring the net primary productivity (NPP) of mangrove plants with high frequency and high precision. Background Art

[0002] As one of the plant communities with the strongest carbon sequestration ability in the global tropical and subtropical regions, mangroves have attracted the attention of ecologists from various countries due to their extremely high net primary productivity. Net primary productivity is the basis of the carbon sequestration ability of a community, which can not only reflect the growth status of the community but also serve as an important indicator of the community's carbon sequestration ability. Currently, net primary productivity has been widely used to estimate the carbon stock in mangroves.

[0003] In the measurement of the net primary productivity of a mangrove community, the fixed plot method is usually combined with the litterfall amount and the increment growth amount (LG) and the light attenuation / gas exchange method (LA) for determination. The LG method is the most widely used, but it has problems such as low monitoring continuity, high cost, and great difficulty in field operation; the LA method is relatively simple to operate, but it still has the limitations of low monitoring continuity and the requirement of a uniform and simple canopy structure during measurement. Whether it is the LG method or the LA method, real-time monitoring of net primary productivity cannot be completed. Therefore, seeking a method that can dynamically monitor net primary productivity with high frequency and high precision can greatly simplify field monitoring operations and enrich the mangrove carbon sink database. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for monitoring the net primary productivity of a mangrove plant community based on stem flow, which has accurate monitoring, high promotion degree, strong operability, low monitoring difficulty, and high continuity, aiming at the problems existing in the prior art such as great difficulty and low continuity in the field monitoring of the net primary productivity of mangroves.

[0005] The present invention includes the formulation of a monitoring plan, monitoring content and methods, monitoring process steps and operation specifications, and a method for calculating net primary productivity. Specifically, it includes the following steps:

[0006] 1) Formulate a monitoring plan for the increment of the carbon pool in coastal wetland sediments, and determine the monitoring scope and zoning; including the reasonable determination of the monitoring area boundary, the subdivision of the monitoring area, the layout of quadrats and the selection of monitoring sample trees, the layout of monitoring stations, the analysis and determination of the carbon pool composition, the determination of the quadrat type, quantity and location, the determination of monitoring indicators, monitoring time and frequency;

[0007] In step 1), the reasonable determination of the monitoring area boundary includes:

[0008] (1) Determine the survey scope according to the survey purpose and objects to ensure that the scope of the monitoring area can fully represent the distribution and growth of typical mangrove plant community trees;

[0009] (2) The boundary of the survey scope is the boundary of the mangrove area under investigation, which is determined through maps, nautical charts, topographic maps, land use type maps, soil and vegetation distribution maps, aerial or satellite remote sensing images, as well as literature and historical survey data; for survey objects lacking data, determine the survey boundary based on on-site reconnaissance and preliminary surveys. After determining the survey boundary, draw a map of the survey scope and mark the coordinates;

[0010] The subdivision of the monitoring area can be based on the following order:

[0011] a) Differences in plant species and plant growth conditions;

[0012] b) Differences in environmental factors such as light and temperature;

[0013] The specific steps for sample plot layout and selection of monitored sample trees are as follows:

[0014] (1) Determine the location of the monitored sample plots: Based on the differences in the community structure and environmental factors (such as light, temperature, soil salinity, etc.) in the monitoring area, set up random sample plots for monitoring;

[0015] (2) According to the monitoring purpose and scope, determine the quantity and density of the monitoring station layouts:

[0016] a) Determine the environmental conditions of the monitoring object area: Observe the environmental characteristics of the monitoring object and determine important environmental elements as monitoring indicators; for example, conduct monitoring based on different light and different soil salinities;

[0017] b) Estimate the number of sample plots: If considering mangrove plant species as monitoring elements, at least 3 replicates should be set up for each species; if monitoring the net primary productivity of two mangroves of the same species with different forest ages, at least 6 replicates should be set up;

[0018] (3) Set up monitoring stations: On the basis of meeting the requirements of survey accuracy, select the sample plots with the smallest area;

[0019] (4) Select monitored sample trees:

[0020] a) Requirements for sample tree traits: Observe the growth of trees in the sample plot, and select individuals that are healthy without diseases, have no shading in the canopy, and whose sapwood thickness is greater than the length of the heat-dissipation type sap flow monitoring probe as sample trees;

[0021] b) Determine the number of sample trees: At least three trees of each species should be selected in each sample plot as sample trees;

[0022] 2) Monitoring of the net primary productivity of mangrove plant communities; using a plant stem sap flow monitoring system to monitor the stem flow rate of sample trees in real time, and using an isotope analyzer to obtain the 13 C isotope compositions of plant leaves and canopy atmosphere within the quadrat respectively. Using a fisheye camera to photograph the canopy, and then using Sidelook 1.1 (an ecological application software in the United States) and GAL (China) software to analyze and calculate the leaf area index; using an increment borer method to measure the sapwood thickness of trees; using a small weather station to record the air temperature and saturation vapor pressure deficit within the quadrat; specifically:

[0023] (1) Monitoring indicators: including the stem flow rate of sample trees, the canopy leaf area index LAI, the 13 C isotope compositions of plant leaves and canopy atmosphere, the sapwood area SA of trees, the environmental temperature T a and the saturation vapor pressure deficit VPD;

[0024] (2) Monitoring time: The stem flow monitoring time is continuous and uninterrupted, and the total monitoring duration depends on the research purpose; the monitoring frequency of the leaf area index and stable isotopes is twice a year, that is, once in the growing season and once in the non-growing season; if the monitoring cannot be carried out as planned due to irresistible factors, it is necessary to make up the measurement as soon as possible after the conditions permit to avoid too long a monitoring interval, which may affect the monitoring results; the environmental conditions should be as consistent as possible each time of monitoring.

[0025] 3) According to the data obtained from the monitoring, calculate the net primary production of the mangrove community. The specific calculation method is as follows:

[0026] (1) According to the temperature difference change between the heating end and the reference end of the heat-dissipation sap flow probe, calculate the volume of liquid flowing through the trunk per unit area per unit time:

[0027]

[0028] Among them, F d represents the stem flow density of the sample tree; ΔT is the temperature difference between the heating end and the reference end of the sensor; ΔT max is the maximum temperature difference between the heating end and the reference end of the sensor, and at this time the stem flow can be regarded as zero;

[0029] (2) Calculate the water consumption at the stand level of mangrove plants:

[0030]

[0031] Among them, SWU represents the stand water consumption of the monitored species; SA represents the sapwood area of the tree; i represents the sample tree; is the density of water (0.998 g / cm 3 ); A is the area of the monitored quadrat;

[0032] (3) Convert the water consumption of the forest stand into the transpiration of the forest stand per unit leaf area:

[0033]

[0034] where LAI is the leaf area index and A is the area of the monitoring plot;

[0035] (4) Calculate the average canopy stomatal conductance of the studied forest stand:

[0036]

[0037] where, is the density of water (0.998 g·cm -3 ); G v is the universal gas constant adjusted for water vapor; T a is the air temperature and D is the vapor pressure deficit;

[0038] (5) Calculate the stomatal carbon dioxide conductance according to the equivalent relationship;

[0039]

[0040]

[0041] where gH2O is the stomatal water vapor conductance;

[0042] (6) Use isotope fractionation to represent the fractionation of 13 C by plants:

[0043]

[0044] where δ 13 C a is the 13 C isotope composition in the atmosphere; δ 13 C p is the 13 C isotope composition in the leaf sap;

[0045] (7) Estimate the intercellular carbon dioxide concentration in the leaf using Δ:

[0046]

[0047] where 4.4 represents the fractionation (4.4%) that occurs when carbon dioxide diffuses through the stomata, C i represents the intercellular CO2 concentration, and C a represents the atmospheric CO2 concentration;

[0048] (8) Calculate the net primary productivity of the monitored mangroves:

[0049]

[0050] Among them, 33.1% represents the proportion of the net primary production of mangroves in the total primary production.

[0051] Furthermore, the layout of the monitoring quadrats shall follow the following principles:

[0052] a) The sample trees for stem flow monitoring should be arranged in the vegetation monitoring quadrats, and the area of the monitoring quadrats shall not be less than 10 m × 10 m; installing benchmark poles at the four corners of the quadrat is conducive to clearly marking the boundaries;

[0053] b) Record the name of the administrative division and the specific geographical location where the monitoring quadrat is located, as well as the detailed information of the quadrat and the sample trees, including the number, geographical location, vegetation type, environmental characteristics, tree diameter at breast height, height, and crown width.

[0054] The following points need to be noted during the measurement:

[0055] a) The length of the heat dissipation type stem flow probe should be selected according to the sapwood thickness of the monitored sample tree, and the probe length shall not exceed the sapwood thickness of the sample tree;

[0056] b) When installing the probe, it should be ensured that it is inserted firmly. After installation, the area where the probe is installed should be wrapped with a radiation-proof film and a waterproof film to reduce the influence of environmental factors such as sunlight and precipitation on the monitoring results;

[0057] c) When installing the probe, the heating end should be kept on top and the reference end should be at the bottom; after installation, the temperature difference between the heating end and the reference end of the probe needs to be adjusted through the monitoring system host so that the maximum temperature difference at the minimum stem flow (at night) does not exceed 7°C.

[0058] When collecting samples, for plant leaf samples, four sunny branches should be randomly selected for each species, and the second or third pair of mature leaves should be collected from top to bottom of the branches. After the leaves are washed with ultrapure water, they are dried to a constant weight at 60°C, ground into powder, and passed through a 60-mesh sieve for stable isotope determination.

[0059] For atmospheric samples, four points should be randomly selected as repeated samples in the canopy of each species, with a distance of about 8 meters between each point. A gas pump connected to a silica gel tube about 10 m long is used for collection. From sunrise to sunset (6:00 - 18:00), the gas is collected into the sample bottle every 2 h. The atmospheric samples should be measured immediately after being collected for one day to avoid inaccurate measurement results.

[0060] When measuring the canopy leaf area index, when obtaining the canopy photos using a fisheye camera, an area with consistent vegetation growth and no obstruction within the quadrat should be selected, and a camera equipped with a fisheye lens should be installed 1 meter above the ground to obtain the photos of the forest canopy.

[0061] When measuring the sapwood thickness of trees using an increment borer, at about 1.3 m above the ground (breast height position) on the tree trunk, the increment borer is drilled perpendicular to the tree trunk surface until it penetrates through the sapwood and enters the heartwood to a certain depth. Then, the wood core is taken out, and the boundary between the sapwood and the heartwood is distinguished according to characteristics such as color and texture. Tools such as a ruler or a microscope are used to measure the width of the sapwood on the wood core. If the monitored object is a diffuse-porous tree species, the breast-height cross-sectional area can be used to replace the sapwood area.

[0062] This method is not only applicable to the monitoring of the net primary productivity of mangrove communities but also equally applicable to the monitoring of the net primary productivity of terrestrial woody plant communities.

[0063] Except that the proportion of community net primary production in total primary production needs to be determined according to the specific situation of different communities, the method applied is the same as the increment monitoring method.

[0064] As an important part of the blue carbon ecosystem, mangroves have strong carbon sequestration potential and make important contributions to mitigating global warming. Estimating the net primary productivity of mangroves is of great significance for evaluating their contributions to the global carbon budget and addressing climate change. Mangroves are widely distributed with a large latitude span. Because they grow in the intertidal zone, mangroves face environmental conditions of high salinity, periodic flooding, and frequent wind and waves. This environmental characteristic makes the dynamic monitoring of net primary productivity with high precision and continuity in the field a technical problem. The monitoring of the present invention has good real-time performance and high credibility. Compared with traditional methods such as the fixed plot method combined with litterfall amount, increment growth amount, and light attenuation / gas exchange method, the present invention is more efficient and convenient and can conduct long-term continuous monitoring. The present invention is suitable for the monitoring work of the net primary productivity of mangrove communities and can better solve the technical problems of the net primary productivity of mangrove communities. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] Figure 1 It is a schematic diagram of the overall framework of an embodiment of the present invention.

[0066] Figure 2 It is an example diagram of the instrument layout and sampling method in an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0067] In order to make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0068] As Figure 1 shown, the embodiment of the present invention gives the general regulations, the stem flow rate of sample trees, the canopy leaf area index LAI, and the 13Basic contents and requirements such as C isotope composition, sapwood area SA of sample trees, and calculation method of net primary productivity. The implementation of the present invention includes steps such as formulation of monitoring plan, monitoring contents and methods, steps and operation specifications of monitoring process, and calculation method of net primary productivity. As Figure 2 Arrange instruments for sampling as shown.

[0069] I. Principles and technical design for monitoring net primary productivity of mangrove plant communities based on stemflow:

[0070] 1) The monitoring of net primary productivity of mangrove plant communities based on stemflow should follow the following principles:

[0071] a) Scientificity: The technical methods adopted in the monitoring should be scientific and rigorous, making full use of the carbohydrate relationship and photosynthesis characteristics of mangrove plants;

[0072] b) Systematicness: The monitoring should start from the integrity of the mangrove plant community, fully considering the interactions among various elements within the system, the interactions and organic connections between the system and the environment;

[0073] c) Representativeness: The sample plots set in the monitoring should have good representativeness, and the development status of the monitoring sample trees should be good, which can reflect the basic conditions of the monitored species;

[0074] d) Accuracy: The acquisition of data such as relevant monitoring indicators and environmental indicators of the monitoring area should be accurate and reliable, which can objectively reflect the current situation.

[0075] 2) From the perspective of technical design, clear project objectives will directly affect the design and implementation of the process. The technical design includes the following considerations:

[0076] a) Fully understand the expected objectives of the project;

[0077] b) Compile a reasonable field monitoring plan according to the objectives;

[0078] c) Design a field sampling plan for the required samples;

[0079] d) Design laboratory analysis methods for the samples;

[0080] II. Compilation of monitoring plan, monitoring scope and zoning for net primary productivity of mangrove plant communities based on stemflow:

[0081] 1) The monitoring plan for community net primary productivity should be continuous and reasonable, mainly including the following five steps:

[0082] a) Reasonable determination of the boundary of the monitoring area;

[0083] b) Subdivision of the monitoring area;

[0084] c) Analysis and determination of species composition;

[0085] d) Determination of quadrat type, quantity, and location;

[0086] e) Determination of monitoring frequency.

[0087] 2) The delimitation of the monitoring area boundary is determined by the scope and objectives of the monitoring, mainly based on:

[0088] a) Determine the survey scope according to the survey purpose and object to ensure that the monitoring area can fully represent the distribution and growth of typical mangrove plant community trees;

[0089] b) The boundary of the survey scope is the boundary of the surveyed mangrove area, which is determined through maps, nautical charts, topographic maps, land use type maps, soil and vegetation distribution maps, aerial or satellite remote sensing images, as well as literature and historical survey data; for survey objects lacking data, determine the survey boundary based on on-site investigation and preliminary survey. After determining the survey boundary, draw a map of the survey scope and mark the coordinates;

[0090] 3) The monitoring sub - areas are based on the following order:

[0091] a) Differences in plant species and plant growth conditions;

[0092] b) Differences in environmental factors such as light and temperature;

[0093] c) Other factors that may affect the monitoring results;

[0094] 4) The layout of monitoring quadrats should adopt the random quadrat method. Within the monitoring area, randomly select areas where plant individuals are evenly distributed and in good growth conditions to set up monitoring quadrats. The density of survey quadrats is related to the purpose and scope of the monitoring and should meet the following requirements:

[0095] a) Determine the environmental conditions of the monitoring object area: Observe the environmental characteristics of the monitoring object area and determine important environmental elements as monitoring indicators; for example, monitor according to different light and different soil salinities;

[0096] b) Estimate the number of quadrats: The number of monitoring quadrats depends on the monitoring purpose;

[0097] Example: If considering mangrove plant species as monitoring elements, at least 3 replicates should be set up for each species; if monitoring the net primary productivity of two mangroves of the same species but different forest ages, at least 6 replicates should be set up;

[0098] 5) Requirements for setting up monitoring stations:

[0099] a) On the basis of meeting the requirements of survey accuracy, select the quadrats with the smallest area;

[0100] b) The monitored quadrat area shall not be less than 10 m × 10 m;

[0101] c) It shall meet the requirements of ecological environment protection and minimize the interference and damage to mangroves.

[0102] III. Contents, methods and time frequencies for monitoring the net primary productivity of mangrove plant communities based on stem flow:

[0103] 1) Monitoring contents and methods:

[0104] The monitoring contents and methods for the net primary productivity of mangrove plant communities based on stem flow are shown in Table 1.

[0105] Table 1

[0106]

[0107] Monitoring the net primary productivity of mangrove plant communities based on stem flow requires measuring the real-time stem flow rate of sample trees, canopy leaf area index (LAI), the 13 C isotope composition of plant leaves and canopy atmosphere, sapwood area (SA) of trees, environmental temperature (T a ), vapor pressure deficit (VPD), etc.

[0108] 2) Monitoring time and frequency:

[0109] Stem flow monitoring is continuous and uninterrupted, and the total monitoring duration depends on the research purpose; the monitoring frequency of leaf area index and stable isotopes is twice a year (both change little in a short period), that is, once in the growing season and once in the non-growing season; if the monitoring cannot be carried out as planned due to irresistible factors, it is necessary to make up the measurement as soon as possible after the conditions permit to avoid too long a monitoring interval, which may affect the monitoring results; the environmental conditions should be as consistent as possible during each monitoring.

[0110] IV. Calculation method for the net primary productivity of mangrove plant communities based on stem flow:

[0111] The calculation of the net primary productivity of mangrove plant communities based on stem flow is mainly divided into 3 steps. In the first step, the stem flow density (F d ) of sample trees is calculated through the monitoring data of the heat dissipation type stem flow measurement probe; in the second step, the stomatal CO2 conductance (gCO2) is deduced by using the sapwood area (SA) of sample trees and the stand leaf area index (LAI); in the third step, the intercellular carbon dioxide concentration (C i ) in leaves is deduced by using isotope analysis; in the fourth step, the net primary productivity (NPP) of mangrove plant communities is calculated through the formula.

[0112] 1) Stem flow density (F d )

[0113] The thermal dissipation probe (TDP) consists of two probes, a heating end and a reference end. According to its working principle, the heating end uses voltage to heat the probe, while the reference end is not heated. When the two probes are inserted into the sample tree, there is a correlation between the sap flow rate of the sample tree and the temperature difference between the two probes. According to the relevant formula, the sap flow density (F d ) of the sample tree can be calculated.

[0114] (1)

[0115] In the formula:

[0116] F d ——Sap flow density of the sample tree (m·s -1 );

[0117] ΔT——Temperature difference between the heating end and the reference end of the sensor (°C);

[0118] ΔTmax——Maximum temperature difference between the heating end and the reference end of the sensor, at this time the sap flow rate can be regarded as zero (°C);

[0119] 2) Estimate the average canopy stomatal conductance (G s );

[0120] The specific estimation steps are as follows:

[0121] a) Calculate the water consumption at the stand level of mangrove plants:

[0122] (2)

[0123] In the formula:

[0124] SWU——Water consumption at the stand level of the monitored species (g·s -1 ·m -2 );

[0125] SA——Cross-sectional area of the tree sapwood (cm 2 );

[0126] i——Sample tree;

[0127] ——Density of water (0.998 g·cm -3 );

[0128] A——Area of the monitored sample plot (m 2 );

[0129] b) Convert the stand water consumption to the stand transpiration per unit leaf area (E L ):

[0130] (3)

[0131] In the formula:

[0132] EL——stand transpiration (mm·s -1 );

[0133] LAI——leaf area index of forest canopy;

[0134] c) Calculate the average forest canopy stomatal conductance of the study stand:

[0135] (4)

[0136] In the formula:

[0137] G s ——average forest canopy stomatal conductance (mmol·H2O·m -2 ·s -1 );

[0138] ——density of water (0.998 g·cm -3 );

[0139] G v ——universal gas constant adjusted for water vapor (462 cm 3 ·kPa·K -1 ·g - 1 );

[0140] T a ——air temperature (°C);

[0141] D——vapor pressure deficit (KPa);

[0142] d) Calculate the stomatal carbon dioxide conductance (gCO2) according to the equivalent relationship:

[0143] (5)

[0144] (6)

[0145] In the formula:

[0146] gH2O——stomatal water vapor conductance (mol·m⁻²·s⁻¹);

[0147] gCO2——stomatal carbon dioxide conductance (mol·m⁻²·s⁻¹);

[0148] 3) Use the isotope analysis method to estimate the intercellular carbon dioxide concentration in leaves (C i )

[0149] Samples of plant leaves and canopy atmosphere were collected once each in the growing season and the non-growing season. When collecting samples, for plant leaf samples, four sunny branches should be randomly selected for each species, and the second or third pair of mature leaves should be collected from the top of the branch downwards. After being washed with ultrapure water, the leaves were dried to a constant weight at 60 °C, ground into powder, and passed through a 60-mesh sieve for stable isotope determination;

[0150] For atmospheric samples, four points should be randomly selected as replicate samples in the canopy of each species, with a distance of about 8 meters between each point. A gas pump connected to a silica gel tube about 10 meters long was used for collection. From sunrise to sunset (6:00 - 18:00), gas was collected into the sample bottle every 2 hours. The atmospheric samples should be immediately subjected to isotope determination one day after collection to avoid inaccurate measurement results;

[0151] a) The measurement results were calculated using the following formula:

[0152] (7)

[0153] In the formula:

[0154] Δ——Isotope fractionation;

[0155] δ 13 C a ——In the atmosphere 13 C isotope composition;

[0156] δ 13 C p ——In the leaf sap 13 C isotope composition;

[0157] b) Estimate the intercellular carbon dioxide concentration in the leaves using Δ:

[0158] (8)

[0159] In the formula:

[0160] 4.4——Indicates the fractionation (4.4%) that occurs when carbon dioxide diffuses through the stomata;

[0161] C i ——Indicates the intercellular CO2 concentration;

[0162] C a ——Indicates the atmospheric CO2 concentration;

[0163] 4) Calculate the net primary productivity (NPP) of the mangrove plant community:

[0164] (9)

[0165] In the formula:

[0166] NPP——Net Primary Productivity;

[0167] 33.1%——The proportion of mangrove net primary production in total primary production;

[0168] When monitoring the net primary productivity of a mangrove plant community based on stem flow, the following principles should be followed when monitoring the stem flow rate of sample trees:

[0169] a) The length of the heat dissipation type stem flow probe should be selected according to the thickness of the sapwood of the sample tree to be monitored, and the probe length shall not exceed the thickness of the sapwood of the sample tree;

[0170] b) When installing the probe, ensure that it is inserted firmly. After installation, use a radiation-proof film and a waterproof film to wrap and cover the area where the probe is installed to reduce the influence of environmental factors such as sunlight and precipitation on the monitoring results;

[0171] c) When installing the probe, keep the heating end on top and the reference end at the bottom; after installation, adjust the temperature difference between the heating end and the reference end of the probe through the monitoring system host so that the maximum temperature difference at the minimum stem flow (at night) does not exceed 7°C;

[0172] The following gives a specific example to further elaborate the main steps of applying the present invention:

[0173] 1. Select trees: Assume that Sonneratia apetala is used as the research object, and 6 healthy and straight-trunked trees are randomly selected in each quadrat for a one-year sap flow monitoring.

[0174] 2. Measure parameters: Monitor using a heat dissipation probe (TDP30) and measure at 15 mm below the cambium and 1.5 m in height of the tree trunk. Assume that the axial sap flow density (F d ) of the 6 Sonneratia apetala trees are respectively: 1.2×10 -6 , 1.3×10 -6 , 1.15×10 -6 , 1.25×10 -6 , 1.35×10 -6 , 1.22×10 -6 (m·s -1 ).

[0175] 3. Sapwood area (SA): Assume that the average sapwood area of the Sonneratia apetala sample trees is 250 cm 2 .

[0176] 4. Leaf area index (LAI): Assume that the LAI of Sonneratia apetala is 1.6 m²·m -2 .

[0177] 5. Stable isotope determination

[0178] Leaf sample collection: In October and May, randomly select four sun-facing branches from each species, and collect the second pair of mature leaves from the branch tips. After washing with ultrapure water, dry the leaves at 60 °C until constant weight, then grind them into powder and pass through a 60-mesh sieve. The carbon isotope value (δ¹³C p ) of Sonneratia apetala leaves was measured to be -29‰.

[0179] Air sample collection: Randomly select four points from the tree canopies of each species as replicate samples, with each point spaced approximately 8 meters apart. Use a diaphragm pump connected to a silicone tube approximately 10 meters long to collect air samples, and collect samples every two hours from sunrise to sunset (6:00 - 18:00). The atmospheric carbon isotope value (δ¹³C a ) of the Sonneratia apetala area was measured to be 9‰.

[0180] 6. Environmental parameter measurement

[0181] Air temperature (T a ) The average air temperature during the measurement period was 28 °C.

[0182] Vapor pressure deficit (D): The average vapor pressure deficit was 1.8 kPa.

[0183] Ambient carbon dioxide concentration (C a ) The ambient carbon dioxide concentration was 410 μmol·mol -1 .

[0184] Density of water (ρ): The density of water was 0.998 g·cm -3 .

[0185] 7. Calculation of stand water use (SWU):

[0186] For Sonneratia apetala, according to the formula , where n = 6, A = 100 m², ρ = 0.998 g·cm -3 . First, calculate (1.2×10 -6 ×0.025 + 1.3×10 -6 ×0.025 + 1.15×10 -6 ×0.025 + 1.25×10 -6 ×0.025 + 1.35×10 -6 ×0.025 + 1.22×10 -6 ×0.025) = 1.8675×10 -7 m 3 ·s -1 .

[0187] Then the calculated value of SWU ≈ 1.87×10 -6 g·s -1 ·m -2 。

[0188] 8. Calculation of stand transpiration (EL):

[0189] According to the formula ,then EL = ≈ 1.17×10 -8 m s -1 ,that is, 1.17×10 -5 mm·s -1 。

[0190] 9. Calculation of average canopy stomatal conductance (Gs):

[0191] According to the formula ,

[0192] We get: G s = ≈ 88.4 mmol·H2O m -2 ·s -1 。

[0193] 10. Calculation of isotope fractionation (Δ)

[0194] According to the formula ,we get Δ = ≈ 20.63%.

[0195] 11. Calculation of intercellular carbon dioxide concentration (C i ):

[0196] According to the formula Δ = 4.4 + (27.5 - 4.4) × ,we get: 20.63 = 4.4 + (27.5 - 4.4) × ,C i ≈ 283.7 umol·mol -1 。

[0197] 12. Calculation of net primary productivity (NPP)

[0198] According to the formula ,it can be calculated that in this case, NPP = 82.4 g·m -2 ·a -1 。

[0199] This invention provides the general provisions of the monitoring method for the net primary productivity of mangrove plant communities based on stem flow, the monitoring content and methods of mangrove stem flow, the monitoring of stable isotopes of plant leaves and canopy atmosphere, the calculation method of the net primary productivity of mangrove plant communities, and other basic contents and requirements. Compared with other current calculation methods for the net primary productivity of mangrove plant communities, this invention is more efficient and convenient, and can conduct long-term monitoring. It has the characteristics of accurate monitoring, high promotion rate, good real-time performance, etc., and better solves the problems of poor continuity and high operation difficulty existing in the prior art.

[0200] The above embodiments are only preferred embodiments of the present invention and cannot be considered as limiting the scope of implementation of the present invention. All equivalent changes and improvements made in accordance with the scope of the present invention application shall still fall within the scope covered by the patent of the present invention.

Claims

1. A method for monitoring the net primary productivity of mangrove communities based on stemflow of tree trunks, characterized in that It includes the following steps: 1) Formulate a monitoring plan to determine the monitoring scope and zoning; including the reasonable determination of the boundaries of the monitoring area, the subdivision of the monitoring area, the layout of quadrats and the selection of monitored sample trees, and the determination of monitoring indicators, monitoring time and frequency; 2) Monitor the net primary productivity of mangrove plant communities: Use a plant stem sap flow monitoring system to monitor the stem flow rate of sample trees in real time, and use an isotope analyzer to obtain the 13 C isotope composition of plant leaves and canopy atmosphere in the quadrat, use a fish-eye camera to photograph the canopy, and analyze and calculate the leaf area index; Use the increment borer method to measure the sapwood thickness of trees; use a small weather station to record the air temperature and vapor pressure deficit within the quadrat; 3) Based on the data obtained from the monitoring, calculate the net primary production of the mangrove community, including: (1) According to the temperature difference change between the heating end and the reference end of the heat-dissipation sap flow probe, calculate the volume of liquid flowing through the trunk per unit area per unit time: Among them, F d represents the sap flow density of the sample tree; ΔT is the temperature difference between the heating end and the reference end of the sensor; ΔT max is the maximum value of the temperature difference between the heating end and the reference end of the sensor, at this time the sap flow rate is regarded as zero; (2) Calculate the water consumption of the mangrove stand at the stand level: Among them, SWU represents the stand water consumption of the monitored species; SA represents the sapwood area of the tree; i represents the sample tree; is the density of water (0.998 g·cm -3 ); A is the area of the monitored sample plot; (3) Convert the stand water consumption to the stand transpiration per unit leaf area: where LAI is the leaf area index and A is the area of the monitored quadrat; (4) Calculate the average canopy stomatal conductance of the studied stand: Wherein, is the density of water (0.998 g·cm -3 ); G v is the universal gas constant adjusted for water vapor; T a is the air temperature, and D is the vapor pressure deficit; (5) Calculate the stomatal carbon dioxide conductance according to the equivalent relationship; where gH2O is the stomatal water vapor conductance; (6) Using isotope fractionation to represent the fractionation effect of plants on 13 the fractionation of Among them, δ 13 C a is the 13 C isotope composition in the atmosphere; δ 13 C p is the 13 C isotope composition in the leaf sap; (7) Use Δ to estimate the intercellular carbon dioxide concentration in the leaves: Among them, 4.4 represents the fractionation (4.4%) that occurs when carbon dioxide diffuses through stomata, C i represents the intercellular CO2 concentration, C a represents the atmospheric CO2 concentration; (8) Calculate the net primary productivity of the monitored mangrove: where 33.1% represents the proportion of mangrove net primary production in the total primary production.

2. The method for monitoring the net primary productivity of a mangrove plant community based on trunk sap flow according to claim 1, characterized in that In step 1), the reasonable determination of the boundaries of the monitoring area includes: (1) Determine the survey scope according to the survey purpose and object to ensure that the monitoring area can fully represent the distribution and growth of typical mangrove plants; (2) The boundary of the survey scope is the boundary of the surveyed mangrove area, which is determined by maps, nautical charts, topographic maps, land use type maps, soil and vegetation distribution maps, aerial or satellite remote sensing images, as well as literature and historical survey data; for survey objects lacking data, determine the survey boundary based on on-site reconnaissance and preliminary surveys. After the survey boundary is determined, draw a map of the survey scope and mark the coordinates.

3. The method for monitoring the net primary productivity of a mangrove plant community based on trunk sap flow as claimed in claim 1, wherein In step 1), the subdivision of the monitoring area is based on the following order: a) Differences in plant species and plant growth conditions; b) Differences in environmental factors such as light and air temperature.

4. The method for monitoring the net primary productivity of mangrove communities based on stem flow as claimed in claim 1, wherein In step 1), the specific steps for the layout of quadrats and the selection of monitored sample trees are as follows: (1) Determine the location of the monitored quadrats: Based on the differences in the community structure and environmental factors of the monitoring area, set up random quadrats for monitoring; environmental factors include light, air temperature, and soil salinity; (2) According to the monitoring purpose and scope, determine the number and density of the monitoring station layouts: a) Determine the environmental characteristics of the monitored object area: Observe the environmental characteristics of the area where the monitored object is located and determine important environmental elements as monitoring indicators; For example: Monitor according to different light and different soil salinities; b) Estimate the number of quadrats: If considering mangrove plant species as monitoring elements, at least 3 replicates should be set up for each species; if monitoring the net primary productivity of two mangroves of the same species with different forest ages, at least 6 replicates should be set up; (3) Set up the monitored quadrats: Based on meeting the requirements of the survey accuracy, select the quadrats with the smallest area; (4) Select the monitored sample trees: a) Requirements for sample tree traits: Observe the growth of trees in the quadrat, and select individuals that are healthy without diseases, have no shading in the canopy, and whose sapwood thickness is greater than the length of the heat-dissipation sap flow monitoring probe as sample trees; b) Determine the number of sample trees: At least three trees of each species in each quadrat should be selected as sample trees.

5. The method for monitoring the net primary productivity of a mangrove plant community based on stem flow as described in claim 1, wherein In step 1), the monitoring indicators include the sap flow rate of the sample tree, the canopy leaf area index LAI, the 13 C isotope composition of the plant leaves and the canopy atmosphere, the sapwood area SA of the sample tree, the environmental temperature T a and the vapor pressure deficit VPD; The monitoring of sap flow is continuous and uninterrupted, and the total monitoring duration depends on the research purpose; the monitoring frequency of leaf area index and stable isotopes is twice a year, that is, once in the growing season and once in the non-growing season; if the monitoring cannot be carried out as planned due to irresistible factors, it is necessary to make up the measurement as soon as possible after the conditions permit to avoid too long a monitoring interval and affecting the monitoring results; the environmental conditions during each monitoring should be as consistent as possible.

6. The method for monitoring the net primary productivity of mangrove communities based on stemflow as claimed in claim 4, wherein The layout of the monitoring quadrats follows the following principles: a) The sample trees for sap flow monitoring should be arranged in the vegetation monitoring quadrats, and the area of the monitoring quadrat should not be less than 10 m × 10 m; installing benchmark poles at the four corners of the quadrat is conducive to clearly marking the boundaries; b) Record the administrative division name and specific geographical location name where the monitoring quadrat is located, as well as the detailed information of the quadrat and sample trees, including number, geographical location, vegetation type, environmental characteristics, tree diameter at breast height, height and crown width; c) When setting up the quadrat, the ecological protection requirements should be considered to reduce the interference and damage to the mangrove ecological environment.

7. The method for monitoring the net primary productivity of a mangrove plant community based on stem flow as claimed in claim 1, wherein In step 2), the sap flow rate of the sample trees is monitored in real time using the plant stem sap flow monitoring system. During the monitoring: a) The length of the heat-dissipation sap flow probe should be selected according to the sapwood thickness of the sample tree being monitored, and the probe length should not exceed the sapwood thickness of the sample tree; b) When installing the probe, it should be ensured that it is inserted firmly. After installation, the area where the probe is installed should be wrapped with anti-radiation film and waterproof film to reduce the influence of environmental factors on the monitoring results; c) When installing the probe, the heating end should be kept on top and the reference end should be at the bottom; after installation, the temperature difference between the heating end and the reference end of the probe should be adjusted through the monitoring system host so that the maximum temperature difference when the sap flow is the smallest does not exceed 7°C.

8. The method for monitoring the net primary productivity of a mangrove plant community based on trunk sap flow as claimed in claim 1, wherein In step 2), the carbon isotope compositions of plant leaves and canopy air within the quadrat are respectively obtained by using an isotope analyzer. During the growing season and the non-growing season, it is necessary to measure the carbon isotope composition of plant leaves and the canopy air within the monitored quadrat. 13 During the growing season and the non-growing season, it is necessary to measure the carbon isotope composition of plant leaves and the canopy air within the monitored quadrat. 13 carbon isotope composition situation; When collecting samples, for plant leaf samples, four sunny branches should be randomly selected for each species, and the second or third pair of mature leaves should be collected from the top to the bottom of the branches. After the leaves are washed with ultrapure water, they are dried to a constant weight at 60°C, ground into powder and passed through a 60-mesh sieve for stable isotope determination; For atmospheric samples, four points should be randomly selected in the canopy of each species as duplicate samples, with a distance of about 8 meters between each point. A gas pump connected to a silica gel tube about 10 meters long is used for collection. From sunrise to 6:00 - 18:00 at sunset, the gas is collected into the sample bottle every 2 hours. The atmospheric sample should be measured immediately after being collected for one day to avoid inaccurate measurement results.

9. The method for monitoring the net primary productivity of a mangrove plant community based on stem flow as claimed in claim 1, wherein In step 2), when using a fish-eye camera to photograph the canopy, when obtaining the canopy photos using the fish-eye camera, select an area in the quadrat where the vegetation growth conditions are consistent and there is no obstruction, and set up a camera equipped with a fish-eye lens 1 meter above the ground to obtain the canopy photos; When measuring the sapwood thickness of trees using an increment borer, follow these steps: At a height of about 1.3 meters from the ground on the tree trunk, drill the increment borer perpendicular to the tree trunk surface until it penetrates through the sapwood and into the heartwood to a certain depth; then remove the wood core, distinguish the boundary between the sapwood and the heartwood based on color and texture, and use tools such as a ruler or microscope to measure the width of the sapwood on the wood core. If the monitored object is a diffuse-porous tree species, then use the basal area at breast height to replace the sapwood area.

10. When the method for monitoring the net primary productivity of a mangrove plant community based on stem flow as described in claim 1 is applied to a terrestrial woody plant community, except that the proportion of community net primary production in total primary production needs to be determined according to the specific situation of different communities, the applied method is the same as the increment monitoring method.

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