A New Perspective on Drought Monitoring: Application of Solar-Induced Chlorophyll Fluorescence (SIF) in Drought Stress Response

幹旱是(shì)一(yī)種(zhǒng)嚴重(zhòng)的環(huán)境(jìng)壓力(lì)，會(huì)削(xiāo)弱植(zhí)物(wù)的(dí)生(shēng)長和(hé)光(guāng)合(hé)作用(yòng)，進而(ér)影(yǐng)響生(shēng)態係(xì)統(tǒng)和(hé)糧(liáng)食安(ān)全。有(yǒu)沒有一種工具(jù)能提前捕(bǔ)捉到(dào)植(zhí)物缺水(shuǐ)時(shí)的微(wēi)妙(miào)變化，幫(bāng)助(zhù)及時監測(cè)幹旱狀況(kuàng)，減輕其(qí)影響呢？

答案是有的，這就是日(rì)光誘(yòu)導葉綠素熒(yíng)光（簡(jiǎn)稱SIF）。可以形象(xiàng)地說(shuō)，SIF是植物釋(shì)放(fàng)的(dí)光(guāng)合作(zuò)用信號，通過(guò)捕捉這(zhè)束微(wēi)弱(ruò)的(dí)熒(yíng)光，我們能實時感(gǎn)知作物(wù)的(dí)健康(kāng)狀(zhuàng)態和幹旱脅迫響應。

Drought is a severe environmental stress that impairs plant growth and photosynthesis, thereby affecting ecosystems and food security. Is there a tool that can detect subtle changes in plants during water deficits early, enabling timely drought monitoring and mitigation?

The answer lies in solar-induced chlorophyll fluorescence (SIF), a signal emitted by plants during photosynthesis. By capturing this faint fluorescence, we can monitor crop health and drought stress responses in real time.

簡單(dān)說說(shuō)SIF

我們(mén)之前(qián)的文章(zhāng)已(yǐ)經(jīng)詳(xiáng)細介紹過(guò)，SIF是在光合作用過程中，葉綠(lǜ)素(sù)被激(jī)發後釋放出的(dí)熒光信號(hào)。它能直接反(fǎn)映光合(hé)作(zuò)用(yòng)的(dí)活躍(yuè)度，是(shì)監測植(zhí)物生理(lǐ)狀態的黃金指標(biāo)。

那(nà)麼，怎麼捕捉(zhuō)這種(zhǒng)幾(jī)乎肉(ròu)眼(yǎn)不可見的熒(yíng)光(guāng)呢？研究人員開發了多種技術手段，從地麵(miàn)光譜儀(yí)到高空遙感(gǎn)衛星(xīng)，都(dū)能(néng)測(cè)量SIF。傳統(tǒng)的衛星雖(suī)然(rán)覆(fù)蓋廣，但(dàn)空間和時間(jiān)分(fēn)辨率有(yǒu)限。愛(ài)博能(néng)推出(chū)了在綫(xiàn)式(shì)和無人(rén)機載(zǎi)的日光誘(yòu)導葉綠(lǜ)素(sù)熒光(guāng)(SIF)觀(guān)測係統，實現(xiàn)多尺(chǐ)度觀測，可(kě)直接獲(huò)得日光誘(yòu)導葉(yè)綠(lǜ)素熒光，光(guāng)合作(zuò)用速(sù)率，歸(guī)一化(huà)植被(bèi)指(zhǐ)數(shù)，增(zēng)強(qiáng)植被(bèi)指數等參數。

To briefly explain SIF, it is the fluorescent signal released when chlorophyll molecules are excited during photosynthesis. Because SIF directly reflects photosynthetic activity, it serves as a valuable indicator for assessing plant physiological status.

How do we capture this nearly invisible fluorescence? Researchers have developed various technologies ranging from ground-based spectrometers to airborne and satellite remote sensing platforms capable of measuring SIF. Conventional satellites offer broad coverage but are limited in spatial and temporal resolution. The company EXPONENT (愛博(bó)能(néng)) has developed both online and drone-mounted SIF Monitoring systems that enable multi-scale monitoring and provide real-time measurements of SIF, photosynthetic rate, normalized vegetation index (NDVI), enhanced vegetation index (EVI), and other parameters.

愛博能SIF係列產品(pǐn) / EXPONENT SIF Product Series

SIF如何幫我(wǒ)們(mén)監(jiān)測(cè)幹旱？ / How does SIF help monitor drought?

研(yán)究人員(yuán)為了認識SIF與幹(gān)旱(hàn)脅迫(pò)之(zhī)間(jiān)的(dí)關(guān)係，可謂(wèi)使出(chū)了渾身解(jiě)數。其(qí)中(zhōng)，一個(gè)中國團(tuán)隊(duì)搭(dā)建(jiàn)了一個實驗田和智能(néng)灌(guàn)溉控製(zhì)係統(tǒng)，結合地麵(miàn)實測與(yǔ)SIF觀測，來動態(tài)監控作物水(shuǐ)分狀況。

他(tā)們(mén)讓(ràng)冬小(xiǎo)麥經(jīng)歷(lì)4種(zhǒng)程(chéng)度(dù)的幹旱脅迫，實時采(cǎi)集SIF信號，同(tóng)時監測光(guāng)合(hé)速(sù)率和其(qí)他(tā)生(shēng)理(lǐ)指(zhǐ)標。結果發現(xiàn)，SIF與(yǔ)光合速率(shuài)呈高度(dù)正相(xiāng)關(guān)。更重要(yào)的是(shì)，SIF對(duì)輕度幹旱的響(xiǎng)應(yīng)比(bǐ)傳統(tǒng)土(tǔ)壤水(shuǐ)分測(cè)量(liáng)更早更敏感(gǎn)，提前(qián)預警能力(lì)較(jiào)強(qiáng)。這(zhè)項研究(jiū)不僅驗(yàn)證了SIF作(zuò)為幹旱監測指(zhǐ)標(biāo)的(dí)科學(xué)性(xìng)，還(huán)為(wéi)智能(néng)農(nóng)業灌(guàn)溉提供了數據支持，具有(yǒu)很(hěn)高(gāo)的(dí)應(yīng)用價值(zhí)。

To better understand the relationship between SIF and drought stress, researchers have employed comprehensive methods. One Chinese team established an experimental field with an intelligent irrigation control system, combining in-situ measurements with SIF observations to dynamically monitor crop water status.

They subjected winter wheat to four levels of drought stress, collecting real-time SIF data along with photosynthetic rate and other physiological metrics. The results showed a strong positive correlation between SIF and photosynthetic rate. Importantly, SIF responded earlier and more sensitively to mild drought than traditional soil moisture measurements, providing effective early warning capability. This study confirmed the scientific validity of SIF as a drought monitoring indicator and provided valuable data support for precision irrigation in smart agriculture.

實驗(yàn)田示意圖(tú) / Experimental Field Diagram

不(bù)同幹(gān)旱(hàn)脅(xié)迫下(xià)的(dí)響應(yīng)（T1，T2，T3和T4分別代(dài)表：澆水充足(zú)，輕(qīng)度(dù)幹旱(hàn)，中(zhōng)度幹旱(hàn)和重度幹旱）。不同字母(mǔ)的(dí)值表(biǎo)示(shì)在(zài) p < 0.05 處(chǔ)存在顯(xiǎn)著差異。圖中的空(kōng)心(xīn)塊(kuài)代(dài)表平(píng)均值，使用(yòng)從種植後(hòu)177~223天收集的數據計算得(dé)到(dào)。可以看出SIF對T2輕(qīng)度幹(gān)旱(hàn)的響應更加敏(mǐn)感。

Responses under Different Drought Stress Levels (T1, T2, T3, and T4 represent well-watered, mild drought, moderate drought, and severe drought, respectively). Different letters indicate significant differences at p < 0.05. Hollow squares in the figure represent the mean values, calculated from data collected between 177 and 223 days after planting. It can be observed that SIF shows greater sensitivity to mild drought (T2).

不(bù)同(tóng)水分脅(xié)迫下，不(bù)同(tóng)參數(shù)的季(jì)節變化。T1，T2，T3和(hé)T4分別(bié)代(dài)表(biǎo)：澆(jiāo)水充足，輕(qīng)度(dù)幹旱(hàn)，中度幹旱和(hé)重度幹(gān)旱。所(suǒ)有(yǒu)值均從9點到16點的平(píng)均值(zhí)。橫坐標(biāo)DAP是(shì)指種植後的(dí)天(tiān)數。可以(yǐ)看出(chū)SIF則呈現波(bō)動變(biàn)化，對土壤水分(fēn)更敏(mǐn)感。

Seasonal Variation of Different Parameters under Various Water Stress Conditions. T1, T2, T3, and T4 represent well-watered, mild drought, moderate drought, and severe drought, respectively. All values are averages from 9 a.m. to 4 p.m. The x-axis DAP refers to Days After Planting. SIF exhibits fluctuations and is more sensitive to soil moisture changes.

而另一個(gè)團隊(duì)，將(jiāng)新疆(jiāng)地區(qū)作為(wéi)研究對象(xiàng)，由於新(xīn)疆屬於大(dà)陸(lù)性(xìng)幹旱(hàn)和(hé)半幹(gān)旱氣(qì)候區(qū)域，年降(jiàng)水(shuǐ)稀少，蒸(zhēng)發量(liáng)大(dà)，且農業(yè)高(gāo)度依(yī)賴灌溉(gài)，因此幹旱對作物生長的(dí)影響尤為顯(xiǎn)著。科研人員結合(hé)2001年至(zhì)2020年長達(dá)20年的(dí)遙(yáo)感(gǎn)SIF數(shù)據(jù)與當地實地氣象(xiàng)及植(zhí)被監(jiān)測(cè)數(shù)據(jù)，利用時間序(xù)列分(fēn)析(xī)，空間(jiān)疊加和Mann-Kendall趨勢檢(jiǎn)驗(yàn)等統(tǒng)計(jì)方(fāng)法(fǎ)，深入剖(pōu)析SIF信號在不同(tóng)時(shí)空(kōng)尺(chǐ)度(dù)上的(dí)變化規(guī)律。

研究(jiū)發現SIF值在(zài)幹(gān)旱初期即(jí)顯著(zhù)下(xià)降，其響應速度(dù)快於(yú)傳(chuán)統(tǒng)植被指(zhǐ)數，能(néng)夠第(dì)一時(shí)間(jiān)反映出植(zhí)物光合作用(yòng)的受損(sǔn)程度(dù)；此外(wài)，不(bù)同(tóng)幹旱類(lèi)型(xíng)對(duì)SIF的(dí)影響(xiǎng)存在顯(xiǎn)著差(chà)異，尤其(qí)是土壤水(shuǐ)分(fēn)脅(xié)迫對(duì)SIF的抑(yì)製(zhì)最(zuì)為明(míng)顯。從空(kōng)間視角來(lái)看，幹(gān)旱(hàn)核心區(qū)的SIF波(bō)動更(gēng)為(wéi)劇(jù)烈，表現出顯著(zhù)的區(qū)域差異。

Another research group focused on Xinjiang, a region characterized by a continental arid and semi-arid climate with low annual precipitation, high evaporation, and heavy agricultural reliance on irrigation. Using 20 years (2001–2020) of remote sensing SIF data combined with local meteorological and vegetation monitoring records, they applied time series analysis, spatial overlay, and Mann-Kendall trend tests to examine SIF variations across different spatial and temporal scales.

They found that SIF values declined significantly early in drought events, with a faster response than traditional vegetation indices, thereby promptly indicating reductions in photosynthesis. Different drought types had distinct effects on SIF, with soil moisture stress showing the strongest suppression. Spatially, the drought core areas exhibited greater SIF variability, reflecting pronounced regional differences.

技(jì)術框架(jià) / Technical Framework

類(lèi)似(sì)地，美國的研究人(rén)員(yuán)通(tōng)過衛(wèi)星(xīng)數(shù)據分析(xī)2011年德(dé)克薩(sà)斯(sī)州(zhōu)幹旱和(hé)2012年中部大平(píng)原幹旱，發(fā)現(xiàn)SIF信號(hào)都(dū)在(zài)幹旱(hàn)期(qī)間明顯(xiǎn)減(jiǎn)弱，有效(xiào)反映(yìng)了幹(gān)旱對(duì)植(zhí)被(bèi)光合活(huó)性(xìng)帶來的(dí)抑(yì)製(zhì)作用。

總的來說，這(zhè)些(xiē)研(yán)究(jiū)讓(ràng)我們(mén)看到(dào)SIF不(bù)僅是“植(zhí)物光合(hé)作用(yòng)的即時屏幕"，更是監測(cè)幹旱脅迫的“靈(líng)敏(mǐn)雷達(dá)"，賦(fù)能(néng)智慧農業(yè)提(tí)前(qián)采(cǎi)取(qǔ)措施，保(bǎo)障作(zuò)物(wù)健(jiàn)康(kāng)成長。

Similarly, researchers in the United States analyzed satellite data from the 2011 Texas drought and the 2012 Central Great Plains drought, observing notable SIF declines during these events that effectively represented drought-induced reductions in vegetation photosynthetic activity.

Overall, these studies demonstrate that SIF serves not only as an “instantaneous screen" of plant photosynthesis but also as a highly sensitive “radar" for detecting drought stress, empowering smart agriculture to take proactive measures to safeguard crop health.

愛(ài)博(bó)能(néng)的SIF觀測(cè)係(xì)統 — 農(nóng)業“幹旱預(yù)警(jǐng)專(zhuān)家"

麵對(duì)日益(yì)嚴峻(jùn)的氣候(hòu)挑戰，愛博能(néng)研(yán)發的(dí)日(rì)光(guāng)誘(yòu)導葉(yè)綠素熒(yíng)光(SIF)監測係(xì)統(tǒng)具備(bèi)諸多優(yōu)勢(shì)：

• 高精(jīng)度數(shù)據(jù)捕獲(huò)，采(cǎi)用高分(fēn)辨，高(gāo)靈敏(mǐn)度，高穩定(dìng)性(xìng)溫(wēn)漂的國產(chǎn)化光譜(pǔ)儀(yí)；

• 多(duō)尺度監測，提供在綫式(shì)和無(wú)人(rén)機(jī)載(zǎi)式監測係統(tǒng)；

• 全天候監測能力(lì)，在綫(xiàn)式監測係(xì)統(tǒng)打(dǎ)破時(shí)間(jiān)和地(dì)理限製，實現連續(xù)動(dòng)態觀察；

• 定(dìng)製(zhì)服(fú)務，滿足不(bù)同作物(wù)和(hé)區域需求(qiú)。

EXPONENT’s SIF Monitoring System — An Agricultural “Drought Early Warning Expert"

In response to increasing climate challenges, EXPONENT has developed a solar-induced chlorophyll fluorescence (SIF) monitoring system featuring:

• high-precision data acquisition using domestically produced spectrometers with high resolution, sensitivity, and stable temperature drift;

• multi-scale monitoring with both online and drone-mounted systems;

• all-weather continuous monitoring that overcomes temporal and geographical constraints;

• customizable solutions to meet diverse crop and regional needs.

未來(lái)展(zhǎn)望(wàng)

隨(suí)著人(rén)工(gōng)智能技術的發展，未來(lái)將實現更(gēng)精準(zhǔn)的(dí)作物生理(lǐ)狀(zhuàng)態診斷和產量預估。

如果你也想(xiǎng)了解(jiě)更多關於SIF技術(shù)和愛博(bó)能的日(rì)光(guāng)誘導(dǎo)葉綠素(sù)熒(yíng)光(SIF)監測係(xì)統(tǒng)，歡迎聯(lián)係(xì)我(wǒ)們(mén)，開(kāi)啟智慧農(nóng)業的新篇章(zhāng)！

Future Outlook

With advances in artificial intelligence, future developments will enable even more accurate diagnosis of crop physiological states and yield prediction.

If you want to learn more about SIF technology and EXPONENT’s SIF monitoring system, feel free to contact us and join the new era of smart agriculture!

案例來(lái)源 / Source

1. Zhao et al., Exploring the Ability of Solar-Induced Chlorophyll Fluorescence for Drought Monitoring Based on an Intelligent Irrigation Control System. Remote Sens. 2022, 14, 6157.

2. Xue et al., 2024. Response of solar-induced chlorophyll fluorescence-based spatial and temporal evolution of vegetation in Xinjiang to multiscale drought. Front. Plant Sci. 15:1418396.

3. Sun et al., 2015, Drought onset mechanisms revealed by satellite solar-induced chlorophyll fluorescence: Insights from two contrasting extreme events, J. Geophys. Res. Biogeosci., 120, 2427–2440.