Plant "Fluorescence": Understanding Plant Health Beyond the Naked Eye

在(zài)日常農業生(shēng)產(chǎn)與(yǔ)生態環(huán)境(jìng)監測(cè)中
，農(nóng)作(zuò)物(wù)或植(zhí)被的(dí)健康狀(zhuàng)況常常(cháng)出現一些(xiē)表麵上難以察(chá)覺的變化
。想(xiǎng)象這樣一(yī)個(gè)場景：肉眼(yǎn)觀察並發(fā)現(xiàn)沒有明顯(xiǎn)的病蟲(chóng)害或營(yíng)養(yǎng)缺陷
，但田間產(chǎn)量卻出現(xiàn)了下滑(huá)
。傳(chuán)統的植(zhí)被(bèi)指數（例如NDVI）在此類情況下有(yǒu)時難(nán)以(yǐ)及時捕(bǔ)捉到植物內部的光合(hé)作(zuò)用(yòng)變(biàn)化
，從而導(dǎo)致(zhì)對(duì)產量乃(nǎi)至(zhì)生(shēng)態係(xì)統健康狀態的錯誤判(pàn)斷(duàn)
。

正是(shì)在這種背景(jǐng)下(xià)
，日光誘導葉(yè)綠素(sù)熒光（SIF）技(jì)術應運而(ér)生
，並(bìng)迅速成為(wéi)科(kē)學(xué)界(jiè)和(hé)產業(yè)界(jiè)關注的焦點
。這項(xiàng)技術(shù)直接(jiē)反(fǎn)映(yìng)了(liǎo)植物(wù)光(guāng)合作(zuò)用的(dí)真(zhēn)實動態(tài)
，為檢(jiǎn)測(cè)植(zhí)物壓(yā)力(lì)，預測作物生(shēng)產(chǎn)力以及評估(gū)生態係(xì)統功能(néng)提(tí)供(gōng)了(liǎo)一種全新的，精確的監測(cè)手段
。SIF技術作為(wéi)一種(zhǒng)“植(zhí)物的(dí)心電圖(tú)"
，能(néng)夠(gòu)捕捉到(dào)植物(wù)在(zài)光合(hé)作(zuò)用(yòng)過程(chéng)中釋放出(chū)的(dí)微弱熒(yíng)光(guāng)信號
。這種信(xìn)號與傳(chuán)統(tǒng)通(tōng)過反(fǎn)射獲得的植(zhí)被指(zhǐ)數存(cún)在本(běn)質(zhì)不(bù)同
，其優勢在於(yú)能(néng)直(zhí)接反映植(zhí)物內(nèi)在生(shēng)理(lǐ)活動
，而非僅(jǐn)僅(jǐn)依(yī)賴葉(yè)麵積，綠度等表(biǎo)麵特(tè)征
。

In daily agricultural production and ecological environment monitoring, crops and vegetation often exhibit subtle changes in their health status that are difficult to detect with the naked eye. Imagine a scenario: you observe a field with no obvious signs of pests, diseases, or nutrient deficiencies, yet the yield is declining. Traditional vegetation indices, such as NDVI, sometimes fail to capture the underlying photosynthetic changes in plants in such cases, leading to incorrect assessments of yield and even ecosystem health.

It is against this backdrop that Solar-Induced Chlorophyll Fluorescence (SIF) technology has emerged and rapidly become a focal point in the scientific and industrial communities. This technology directly reflects the true dynamics of plant photosynthesis, providing a novel and precise monitoring tool for detecting plant stress, predicting crop productivity, and evaluating ecosystem function. SIF technology, acting as a "plant electrocardiogram", captures the faint fluorescence signals emitted by plants during photosynthesis. This signal is fundamentally different from traditional vegetation indices derived from reflection, as its advantage lies in directly reflecting the plant's intrinsic physiological activity, rather than merely relying on surface characteristics like leaf area or greenness.

土壤-植(zhí)被(bèi)-大氣(qì)連續(xù)統中植被(bèi)尺度的(dí)生(shēng)態過(guò)程(chéng)和(hé)水勢梯度

Ecological Processes and Water Potential Gradients at the Vegetation Scale within the Soil-Vegetation-Atmosphere Continuum

什(shí)麼是日光誘(yòu)導(dǎo)葉綠(lǜ)素(sù)熒光（SIF）？

What is Solar-Induced Chlorophyll Fluorescence (SIF)?

日(rì)光(guāng)誘(yòu)導(dǎo)葉(yè)綠素(sù)熒光(guāng)（Solar-induced chlorophyll fluorescence, SIF）
，是(shì)一種直接(jiē)反(fǎn)映植物光合(hé)作(zuò)用效率的(dí)信號(hào)
，其產生(shēng)過程與光(guāng)合(hé)作(zuò)用(yòng)密切(qiē)相關(guān)
。簡(jiǎn)而言之
，植物(wù)在(zài)吸(xī)收(shōu)太(tài)陽光(guāng)能後
，一(yī)部分能(néng)量(liáng)用(yòng)於光合作用(yòng)
，而另(lìng)一部(bù)分能量則通過熱(rè)散發(fā)或以(yǐ)葉(yè)綠(lǜ)素熒光形式(shì)輻射出來(lái)
。SIF技術通(tōng)過傳(chuán)感器(qì)對這些熒光信(xìn)號(hào)進(jìn)行捕捉和解(jiě)析
，從而(ér)直接(jiē)衡(héng)量光(guāng)合(hé)活動的強弱及其(qí)隨時(shí)間和環境條件(jiàn)的動態變(biàn)化(huà)
。

Solar-Induced Chlorophyll Fluorescence (SIF) is a signal that directly reflects the efficiency of plant photosynthesis. Its generation process is closely linked to photosynthesis. Simply put, after plants absorb solar energy, a portion of this energy is used for photosynthesis, while another portion is dissipated as heat or re-emitted as chlorophyll fluorescence. SIF technology captures and analyzes these fluorescence signals using sensors, thereby directly measuring the intensity of photosynthetic activity and its dynamic changes over time and under varying environmental conditions.

(A) 農田麵積上(shàng)基(jī)於(yú) SIF 的(dí)年(nián)度作物(wù) GPP 估計的空間詳(xiáng)細(xì)信息，(B) 每個網(wǎng)格框(kuàng)的農(nóng)田(tián)麵(miàn)積(jī)比(bǐ)例(lì)

(A) Spatially explicit estimates of annual crop GPP based on SIF over agricultural areas, and (B) the proportion of agricultural area in each grid box

1.1 SIF信號(hào)的形成與檢測(cè)機(jī)製(zhì)

Formation and Detection Mechanism of SIF Signals

在光合(hé)作用過程中(zhōng)
，植被(bèi)吸(xī)收(shōu)了大量太陽(yáng)能後
，為維(wéi)持(chí)光合(hé)平衡(héng)並防(fáng)止能量過剩引起(qǐ)的光損(sǔn)傷(shāng)
，葉綠(lǜ)素會(huì)釋(shì)放(fàng)出(chū)非(fēi)常(cháng)微(wēi)弱的熒光(guāng)信號
。這一熒光信號主要(yào)集中(zhōng)在紅(hóng)光（約(yuē)680nm）和(hé)遠(yuǎn)紅光(guāng)（約740nm）波段
，正是這一(yī)特性使(shǐ)得(dé)SIF成(chéng)為捕捉(zhuō)植物內(nèi)部光合作用活動的重要(yào)手(shǒu)段
。而且(qiě)
，不(bù)同類型的作(zuò)物和自(zì)然(rán)植(zhí)被(bèi)
，其SIF信號(hào)強(qiáng)度(dù)和(hé)動(dòng)態(tài)響應存(cún)在區域性差(chà)異
，如同植物體內(nèi)生(shēng)理(lǐ)狀(zhuàng)態的實時(shí)反饋
。

During photosynthesis, after absorbing a large amount of solar energy, vegetation releases very faint fluorescence signals to maintain photosynthetic balance and prevent photoinhibition caused by excess energy. This fluorescence signal is primarily concentrated in the red light (around 680nm) and far-red light (around 740nm) spectral bands. This specific characteristic makes SIF a crucial means of capturing the internal photosynthetic activity of plants. Furthermore, different types of crops and natural vegetation exhibit regional variations in SIF signal intensity and dynamic response, serving as a real-time feedback of the plant's internal physiological state.

1.2 夫琅禾費暗綫的“井"填充效(xiào)應(yīng)

The "Filling" Effect of Fraunhofer Lines

在(zài)自(zì)然光照條件下
，植被反(fǎn)射的(dí)光譜(pǔ)實際上(shàng)包(bāo)含(hán)了(liǎo)兩個部(bù)分(fēn)：一部(bù)分是葉片對(duì)入(rù)射(shè)太(tài)陽光的反(fǎn)射
，另一部分(fēn)則是植(zhí)被(bèi)自身發射(shè)的日光(guāng)誘(yòu)導(dǎo)葉(yè)綠素熒光(guāng)（SIF）
。雖(suī)然SIF的信(xìn)號非常(cháng)微(wēi)弱
，通(tōng)常不(bù)到(dào)太陽入(rù)射能(néng)量的(dí)1%
，遠(yuǎn)弱於植被的反(fǎn)射(shè)光
，但在特定(dìng)的波(bō)段(duàn)
，我們(mén)可以巧(qiǎo)妙地利(lì)用(yòng)一(yī)個自(zì)然(rán)現(xiàn)象來提(tí)取(qǔ)SIF信號
。這個自(zì)然現象就是(shì)“夫琅(láng)禾(hé)費暗綫(xiàn)"
。由於(yú)太陽和(hé)地球(qiú)大(dà)氣層的(dí)吸(xī)收作(zuò)用
，太(tài)陽光譜(pǔ)中存在一(yī)些非(fēi)常(cháng)狹(xiá)窄(zhǎi)且強度較(jiào)低的(dí)“暗(àn)綫"（寬度為0.1~10nm）
，這些(xiē)就(jiù)是夫琅(láng)禾費(fèi)暗(àn)綫(xiàn)
。在這些暗(àn)綫位置
，太陽光的能量(liáng)顯著(zhù)低於(yú)周圍(wéi)波段
。

葉(yè)綠素(sù)熒光的光譜(pǔ)輻射恰(qià)好會(huì)填(tián)充這(zhè)些(xiē)暗(àn)綫區(qū)域(yù)
，使得在(zài)這(zhè)些暗綫位(wèi)置(zhì)
，SIF的(dí)相(xiāng)對(duì)比例顯著增大
。因此(cǐ)
，將(jiāng)太陽(yáng)輻(fú)射和植被反射光(guāng)譜中(zhōng)某(mǒu)個(gè)波(bō)段(duàn)的夫琅禾費(fèi)暗(àn)綫(xiàn)與(yǔ)相鄰的波(bō)譜之(zhī)間(jiān)的相(xiāng)對強(qiáng)度進行比較
，二者(zhě)之間(jiān)的(dí)差(chà)異就可(kě)以用來(lái)反演出SIF的強度(dù)
。這(zhè)就像(xiàng)在太陽光譜(pǔ)的“凹陷(xiàn)處"找(zhǎo)到了SIF留下的(dí)“填(tián)補(bǔ)"痕(hén)跡
，通(tōng)過測量這種填補(bǔ)的程度(dù)
，我們(mén)就能估(gū)算出SIF的(dí)強度
。

Under natural illumination, the spectrum reflected by vegetation actually comprises two components: one is the reflection of incident solar light by the leaves, and the other is the Solar-Induced Chlorophyll Fluorescence (SIF) emitted by the vegetation itself. Although the SIF signal is very weak, typically less than 1% of the incoming solar energy and much weaker than reflected light, we can cleverly utilize a natural phenomenon to extract the SIF signal at specific wavelengths. This phenomenon is known as "Fraunhofer Lines". Due to the absorption by the sun and the Earth's atmosphere, the solar spectrum contains very narrow and less intense "dark lines" (with widths ranging from 0.1 to 10nm). These are the Fraunhofer lines. At these dark line positions, the solar energy is significantly lower than in the surrounding spectral regions.

The spectral radiation of chlorophyll fluorescence happens to "fill in" these dark line regions, causing the relative proportion of SIF to significantly increase at these Fraunhofer line positions. Therefore, by comparing the relative intensity between a Fraunhofer line and its adjacent spectral region in both the incoming solar radiation and the vegetation's reflected radiance spectra, the difference can be used to retrieve the intensity of SIF. This is akin to finding the "filling" trace left by SIF in the "dips" of the solar spectrum. By measuring the extent of this filling, we can estimate the intensity of SIF.

葉(yè)綠素熒光(guāng)（SIF）對夫琅(láng)和費(fèi)暗(àn)綫的(dí)“井(jǐng)"填(tián)充效應(yīng)

The "In-filling" Effect of Chlorophyll Fluorescence (SIF) on Fraunhofer Lines

SIF：植(zhí)物(wù)的心電(diàn)圖(tú)

SIF: The Plant's Electrocardiogram

從(cóng)前(qián)麵(miàn)的介紹(shào)可知
，SIF能夠更直接，更(gēng)敏感(gǎn)地(dì)反(fǎn)映植物(wù)光合作(zuò)用的(dí)效率和(hé)健康(kāng)狀(zhuàng)況
。SIF可以(yǐ)看(kàn)作(zuò)是植(zhí)物的“心(xīn)電(diàn)圖(tú)"
，用來(lái)監(jiān)測(cè)植物生(shēng)理(lǐ)活(huó)動(dòng)的“脈(mài)搏(bó)"
。憑借這(zhè)個特性
，SIF在(zài)眾(zhòng)多領(lǐng)域展現出*的(dí)應(yīng)用潛力
，以(yǐ)下是(shì)它的(dí)主(zhǔ)要(yào)應(yīng)用方(fāng)向(xiàng)：

As discussed, SIF provides a more direct and sensitive reflection of plant photosynthetic efficiency and health status. SIF can be considered the plant's "electrocardiogram," used to monitor the "pulse" of its physiological activity. With this characteristic, SIF demonstrates powerful application potential in numerous fields. Here are its main application areas:

農業(yè)領(lǐng)域

• 監測作(zuò)物生長：SIF能夠實時反(fǎn)映作物的生長活力
，幫助了解作物的生(shēng)長狀(zhuàng)態(tài)
，及時調(tiáo)整管理(lǐ)措(cuò)施(shī)
。

• 診斷病蟲(chóng)害和(hé)脅迫(pò)：在(zài)作物表現(xiàn)出肉眼可(kě)見(jiàn)的病(bìng)蟲(chóng)害或水分(fēn)脅(xié)迫症(zhèng)狀之(zhī)前
，SIF信號可能已(yǐ)經發(fā)生(shēng)變(biàn)化
，為早期預(yù)警和(hé)精準(zhǔn)施(shī)策提供依據
。

• 優(yōu)化施肥(féi)灌(guàn)溉：根(gēn)據(jù)SIF數據(jù)評估作(zuò)物對(duì)養(yǎng)分和(hé)水(shuǐ)分的(dí)需(xū)求
，實現(xiàn)精準施(shī)肥和(hé)灌溉(gài)
，提高(gāo)資源(yuán)利(lì)用(yòng)效率
，降(jiàng)低生產成(chéng)本
。

• 產量預(yù)估： SIF與作物最終產量(liáng)之間存在(zài)良好的相關性(xìng)
，利(lì)用(yòng)SIF數據可以更(gēng)準(zhǔn)確地(dì)預估(gū)作(zuò)物產量(liáng)
，為(wéi)農業生(shēng)產(chǎn)決策提(tí)供(gōng)支持(chí)
。

Agricultural

• Monitoring Crop Growth: SIF can reflect crop growth vitality in real-time, helping to understand the growth status of crops and adjust management measures promptly.

• Diagnosing Pests, Diseases, and Stress: Before crops exhibit visible symptoms of pests, diseases, or water stress, the SIF signal may have already changed, providing a basis for early warning and precise intervention strategies.

• Optimizing Fertilization and Irrigation: SIF data can be used to assess crop demand for nutrients and water, enabling precise fertilization and irrigation, improving resource utilization efficiency, and reducing production costs.

• Yield Prediction: There is a good correlation between SIF and final crop yield. Utilizing SIF data can lead to more accurate crop yield predictions, supporting agricultural production decisions.

林業(yè)領域(yù)

• 評(píng)估森林(lín)健康(kāng)：通(tōng)過監測(cè)SIF
，可以評估(gū)森林的光(guāng)合(hé)能(néng)力(lì)和健(jiàn)康狀況
，及時發現森林(lín)退化或(huò)病蟲(chóng)害侵襲的區域
。

• 監(jiān)測(cè)森(sēn)林火災風險：幹(gān)旱(hàn)和高溫(wēn)會導(dǎo)致(zhì)森林植被水分(fēn)含量降低(dī)
，光合(hé)作(zuò)用下降(jiàng)
，SIF信號隨之(zhī)減(jiǎn)弱
。利用SIF數(shù)據可(kě)以評估(gū)森(sēn)林的幹(gān)旱程度
，輔(fǔ)助(zhù)進行(háng)森(sēn)林火(huǒ)險預警
。

Forestry

• Assessing Forest Health: By monitoring SIF, the photosynthetic capacity and health status of forests can be evaluated, allowing for the timely identification of areas experiencing degradation or pest and disease outbreaks.

• Monitoring Forest Fire Risk: Drought and high temperatures lead to reduced water content in forest vegetation and decreased photosynthesis, resulting in a weakening of the SIF signal. SIF data can be used to assess the severity of drought in forests and assist in forest fire risk warning.

生(shēng)態研究(jiū)

• 監測(cè)植被(bèi)生產力(lì)：SIF數據可(kě)以用(yòng)於(yú)估算(suàn)區(qū)域(yù)和全球(qiú)尺度(dù)的植被(bèi)總(zǒng)初級(jí)生產力（GPP）
，幫助科學家理(lǐ)解(jiě)陸地(dì)生(shēng)態(tài)係統碳(tàn)循環
，評估(gū)氣(qì)候變化(huà)對植被(bèi)的影(yǐng)響
。

• 研(yán)究生(shēng)態(tài)係統對環(huán)境變化的(dí)響應(yīng)： 利用SIF監測氣(qì)候事(shì)件（如幹旱(hàn)，熱(rè)浪）對(duì)不同(tóng)生態(tài)係(xì)統的(dí)影響
，深入了(liǎo)解生(shēng)態係統的(dí)脆弱(ruò)性和恢(huī)復(fù)能力
。

Ecological

• Monitoring Vegetation Productivity: SIF data can be used to estimate Gross Primary Production (GPP) at regional and global scales, helping scientists understand terrestrial ecosystem carbon cycling and evaluate the impact of climate change on vegetation.

• Studying Ecosystem Responses to Environmental Changes: SIF can be used to monitor the impact of extreme climate events (such as drought and heatwaves) on different ecosystems, providing deeper insights into ecosystem vulnerability and resilience.

預(yù)告 Preview

我們(mén)了解(jiě)了SIF是什(shí)麼(mó)
，它如何產生
。SIF微弱卻(què)蘊(yùn)含(hán)著(zhuó)巨(jù)大(dà)的(dí)信息(xī)量
，它是植物(wù)與我們“對話(huà)"的(dí)一(yī)種特殊(shū)方式(shì)
。這些(xiē)數據能在實際(jì)中發揮哪(nǎ)些(xiē)作用(yòng)呢(ní)？在接下(xià)來的文(wén)章中
，我(wǒ)們將通過具體(tǐ)的應(yīng)用案例(lì)
，展(zhǎn)示(shì)SIF在(zài)農業，林業，生(shēng)態研究(jiū)等領(lǐng)域的巨大(dà)潛(qián)力
。敬請期(qī)待！

We have learned what SIF is and how it is produced. Despite being weak, SIF carries a wealth of information. It is a special way for plants to "communicate" with us. How can this data be applied in practice? In the following articles, we will showcase the immense potential of SIF in agriculture, forestry, ecological research, and other fields through specific application examples. Stay tuned!

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。

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參考論(lùn)文 / Articals

1. Ni. Zhuoya.L. et al., A Review of Retrieving in Sun-Induced Chlorophyll Fluorescence, Advances in Meteorological Science and Technology (2021).

2. L.Guanter,Y.et al., Global and time-resolved monitoring of crop photosynthesis with chlorophyll fluorescence, Proc. Natl. Acad. Sci. U.S.A. 111 (14) E1327-E1333.