Multi-scale Correlation Mechanism Between Crop Chlorophyll Fluorescence And Photosynthesis And Its Response To Water

With the rise of solar-induced chlorophyll fluorescence（SIF）remote sensing,SIF has been widely used in vegetation productivity estimation,stress monitoring,ecosystem carbon sinks and simulation of key parameters of ecosystem models.The advantages is that chlorophyll fluorescence is closely related to the vegetation photosynthesis process.SIF is considered as a non-destructive probe for photosynthesis research.Studies have found that SIF and gross primary productivity（GPP）are statistically linearly correlated at site scale and regional scale.The relationship of SIF and GPP is affected by many factors such as species differences and environmental stress.At present,with the change of the global environment,frequent drought events have seriously affected agricultural production.Therefore,this paper takes two typical food crops,rice（Oryza sativa L.）and maize（Zea mays L.）as the research objects.We conducted field control experiments and establishes near-ground SIF and GPP observation sites.Chlorophyll fluorescence and photosynthesis parameters were measured at photosystem Ⅱ（PSⅡ）,leaf and canopy scales,respectively,to explore the multi-scale correlation mechanism between crop chlorophyll fluorescence and photosynthesis and their response to water.The main research conclusions are as follows:At PSⅡ level,the effects of soil water stress on the photosynthetic energy allocation mechanism of rice（C₃）and maize（C₄）crops were analyzed.The results indicated that the two crops had different regulatory mechanisms in response to soil water stress.Soil water stress led to a significant decrease in photochemical efficiency（Φp）both in rice and maize,but for different reasons.According to the competition model,the energy-related heat dissipation efficiency（Φn）of rice was increased resulting in a decrease inΦp,while the fluorescence efficiency（Φf）and basal heat dissipation efficiency（Φd）of maize were significantly increased by soil water stress.The relationship between chlorophyll fluorescence and photosynthesis in maize and rice on the PSⅡ scale（Φp-Φf）was a linear positive correlation,and the slope of the linear fit was not affected by soil drought and saturated vapor pressure deficit（VPD）.TheΦp/Φf of both crops were mainly regulated byΦp andΦn,while theΦp/Φf of maize was more affected by soil water content under stress.At the leaf scale,the gross photosynthetic rate（Ag）and leaf light utilization efficiency(LUE_leaf)of the two crops were significantly reduced by soil water stress.The response of maize leaf SIF to soil drought was significant in the red band(SIF₆₈₅).Maize leaf SIF yield（SIFy）was significantly changed by drought in both red(SIF₆₈₅y)and infrared(SIF₇₄₀y)bands,while rice SIF and SIFy were not affected by soil drought.The linear relationship between Ag and leaf SIF was stronger in rice than maize,with positive correlation in rice and negative correlation in maize.There was a positive linear correlation between LUE_leaf-SIFy in leaves of the two crops and soil water stress changed the relationship between the two in maize.In this paper,the effects of leaf physiological and environmental factors on leaf-scale chlorophyll fluorescence and photosynthesis were analyzed.The results showed that leaf chlorophyll fluorescence and photosynthesis were related to chlorophyll content（chlab）,leaf nitrogen content（leafN）,absorbed photosynthetically active radiation（APAR）,maximum carboxylation rate（Vcmax）,maximum electron transfer rate（Jmax）,VPD and other factors.There is a linear correlation.At higher VPD,LUEleaf and SIFy vary less and have lower values.At the canopy scale,we found a positive linear correlation between SIF-GPP.Moreover,the linear relationship between GPP,SIF,APAR and VPD were weak.But the linear relationship between GPP/SIF,LUE,SIFy_canopy and VPD was not significant.Canopy LUE,SIFy_canopy and APAR had a good linear relationship,and there also was a positive linear relationship between LUE and SIFy_canopy.This paper found that VPD did not change the linear relationship between GPP-SIF and LUE-SIFy_canopy.In this paper,the influence of environmental factors,physiological factors and canopy structure factors on GPP/SIF was analyzed using the structural variance model.VPD played an important role in limiting the canopy GPP/SIF ratio,and VPD indirectly affected GPP/SIF by affecting gsw,APAR and leafN on a seasonal scale.Overall,GPP/SIF was positively regulated by leafN,APAR and stomatal conductance（gsw）.In this paper,rice and maize were taken as the research objects,and the seasonal changes of chlorophyll fluorescence and photosynthesis parameters of crop leaves were monitored based on field experiments.The effects of water on photosystem-scale,leaf-scale and canopy-scale chlorophyll fluorescence and photosynthesis of two crops and their relationship were analyzed,which provided information for studying the correlation mechanism between SIF and GPP at regional and satellite scales and for SIF-based water research.theoretical support.