Study On The Correlation Mechanism Of Vegetation Chlorophyll Fluorescence And Photosynthesis

Gross Primary Productivity(GPP)is the amount of carbon absorbed by land plants through photosynthesis,which is the largest CO₂ flux between the terrestrial biosphere and the atmosphere and plays an important role in the global carbon cycle and climate change.Therefore,accurate quantification of regional GPP is essential for understanding the interaction between terrestrial ecosystems and the atmosphere.In the past ten years,due to the close physiological relationship between plant chlorophyll fluorescence and photosynthesis,Sun-Induced chlorophyll Fluorescence(SIF)based on satellite inversion has become a new method for estimating vegetation productivity in terrestrial ecosystems.However,the relationship between GPP and SIF is also affected by many factors,such as environmental conditions,canopy structure,sun-sensor geometry,and vegetation functional type.This study explored the correlation mechanism of plant chlorophyll fluorescence and photosynthesis as well as climate regulation at different scales.The main research contents and conclusions are as follows:(1)This research first explored the difference in energy distribution on the vertical gradient of subtropical evergreen coniferous forest and its response to environmental and physiological factors.It is found that there is significant vertical heterogeneity in energy distribution in the canopy,and the heat dissipation at the top of the canopy plays a dominant role in the energy distribution process,while more light energy at the bottom is used for photochemical reactions.The seasonal dynamics of energy distribution are not only regulated by photosynthetically active radiation,but also by leaf chlorophyll content and leaf nitrogen content.We also found that there is vertical heterogeneity in the negative correlation between fluorescence yield and photosynthetic yield at different canopy heights,which may be mainly regulated by the light gradient.There is a negative correlation between fluorescence yield and photosynthetic yield under low light conditions,while the increased heat dissipation under non-low light conditions destroys the balance between fluorescence yield and photosynthetic yield.Therefore,when exploring the relationship between fluorescence and photosynthesis in evergreen forests,it is necessary to consider the vertical difference of light environment and biochemical conditions.(2)Secondly,satellite-based GOME-2 SIF in the terrestrial ecosystem of china was used to explore the temporal and spatial patterns and climate control of GPP,SIF,and GPP/SIF in different climates zones.The study found that GPP and SIF have good temporal and spatial consistency.GPP/SIF has obvious spatial heterogeneity,with high values appearing in the southeast and southwest regions of China,and low values appearing in the North China Plain and the Qinghai-Tibet Plateau.We also found that SIF yield is regulated by the environment.The environmental conditions have similar control patterns and response trends for SIF yield and the light utilization efficiency of GPP,which proves the close connection between SIF and GPP and the potential of using SIF as a proxy for GPP.However,the minimum temperature,the absorption of photosynthetically active radiation by plants,and water conditions will also restrict the changes of GPP/SIF and affect the dynamic relationship between GPP and SIF.(3)Finally,GOME-2 SIF and FLUXCOM GPP and climate data were used to explore the spatial pattern of the global vegetation GPP-SIF relationship in response to climate.The slope(GPP/SIF)and coefficient of determination(R²)of the non-intercept linear regression were used to express the GPP-SIF relationship.The slope contains information about the light energy distribution of fluorescence and photosynthesis.The study found that the slope and R² of the GPP-SIF relationship are spatially heterogeneous.The high slope is mainly distributed in tropical and northern regions,while the high R² is mainly concentrated in the temperate ecosystems of the northern hemisphere.The spatial variation of the GPP-SIF relationship shows obvious climate dependence.The spatial response of the slope to the mean annual precipitation is almost positive linear,while the response to the mean annual photosynthetic active radiation and the mean annual temperature is non-linear.In the climate space,we also found that the GPP-SIF relationship is jointly constrained by environmental variables.In addition,the sensitivity of the GPP-SIF relationship to the self-calibrated Palmer Drought Severity Index(sc PDSI)indicates that the degree of soil dryness and wetness constrains the GPP-SIF relationship,and arid regions exhibit a low slope of R².This may be attributed to the fact that drought has restricted GPP more,and environmental stress will destroy the relationship between fluorescence and photosynthesis by increasing heat dissipation.In summary,our research studies the correlation mechanism of plant chlorophyll fluorescence and photosynthesis and climate regulation from three perspectives:energy distribution in the vertical gradient of the canopy,regional climate control,and climate response to spatial changes.The results show that environmental factors can regulate the relationship between fluorescence and photosynthesis.To accurately quantify the relationship between chlorophyll fluorescence and photosynthesis,the impact of environmental factors cannot be ignored.Our research provides theoretical support for further parameterizing climate factors to improve the accuracy of the SIF-based GPP model.