Solar-Induced Chlorophyll Fluorescence: Enabling Early Warning of Soil Salinization

土壤鹽漬化，是指土壤底層或地下水中的可溶性鹽分隨水分上升至地表，水分蒸發后，鹽分在表層土壤中積累的過程。這就像海水曬鹽一樣，水分被“曬干"了，鹽分卻留了下來。土壤鹽漬化是影響農業生產和生態健康的全球性問題。

Soil salinization refers to the process in which soluble salts from the soil subsurface or groundwater migrate upward with water to the soil surface. After the water evaporates, the salts accumulate in the topsoil. This is similar to sea salt production: the water is "dried out," but the salts remain. Soil salinization is a global issue affecting agricultural production and ecological health.

土壤鹽漬化 / Soil Salinization

鹽脅迫的負面影響主要體現在四個方面：

·水分虧缺與滲透脅迫：土壤鹽分升高導致水勢降低，阻礙根系吸水，引發滲透脅迫，造成植株生理缺水。

·離子毒害：過量鈉離子和氯離子侵入細胞，破壞膜結構和酶活性，干擾正常代謝。

·氧化脅迫：鹽誘導活性氧（ROS）大量產生，引發膜脂過氧化，細胞結構受損，丙二醛（MDA）含量上升。

·光合作用抑制：鹽脅迫降低葉綠素含量、改變色素組成，直接削弱光系統II（PSII）效率，抑制光合碳同化。

The negative impacts of salt stress are mainly manifested in four aspects:

·Water Deficit and Osmotic Stress: Increased soil salinity lowers water potential, hindering water uptake by roots and causing osmotic stress, which leads to physiological water deficiency in plants.

·on Toxicity: Excessive sodium and chloride ions enter cells, disrupting membrane structures and enzyme activity, thereby interfering with normal metabolic processes.

·Oxidative Stress: Salt stress induces the overproduction of reactive oxygen species (ROS), triggering membrane lipid peroxidation, damaging cell structures, and increasing malondialdehyde (MDA) content.

·Inhibition of Photosynthesis: Salt stress reduces chlorophyll content, alters pigment composition, directly impairs the efficiency of photosystem II (PSII), and suppresses photosynthetic carbon assimilation.

其中，光合作用的變化尤為關鍵。而日光誘導葉綠素熒光（SIF）作為光合作用的“副產物"，能夠靈敏地捕捉到鹽脅迫下光合機構的早期響應。

例如，受鹽脅迫的植物葉片往往出現葉綠素含量下降、光合活性會下降，SIF信號也隨之減弱，這種變化比傳統的植被指數（如NDVI）更早、更靈敏，因為植被指數通常反映的是冠層結構或色素含量的變化，而這些變化往往在脅迫發生一段時間后才顯現。

Among these, changes in photosynthesis are particularly critical. As a byproduct of photosynthesis, sun-induced chlorophyll fluorescence (SIF) can sensitively capture the early responses of the photosynthetic apparatus under salt stress.

For example, salt-stressed plants often exhibit decreased chlorophyll content and reduced photosynthetic activity, accompanied by a decline in SIF signals. These changes occur earlier and are more sensitive than traditional vegetation indices (such as NDVI), as vegetation indices typically reflect alterations in canopy structure or pigment content, which often become apparent only after the stress has persisted for some time.

日光誘導葉綠素熒光的產生 / Generation of Solar-Induced Chlorophyll Fluorescence

西北農林科技大學基于全球OCO-2的SIF產品（GOSIF）的SIF觀測時間序列（2000 ～ 2020）的標準化日致葉綠素流失指數（SIFI）來建立土壤鹽度模型。下圖是該課題組得出的SIF觀測對土壤鹽度估算的評價。

Using the standardized SIF-based loss index (SIFI) derived from the global OCO-2 SIF product (GOSIF) time series (2000–2020), researchers from Northwest A&F University developed a model for estimating soil salinity. The figure below shows the evaluation of SIF observations for soil salinity estimation by this research team.

(a)是典型區域和非典型區域的分布；(b)是SIF觀測對受鹽影響土壤的分類精度；(c)～(d)為SIF觀測的分類結果。

(a) Distribution of typical and atypical regions; (b) Classification accuracy of SIF observations for salt-affected soils; (c)?(d) Classification results based on SIF observations.

新疆的科研機構也利用日光誘導葉綠素熒光來捕捉新疆和中亞地區的植物對鹽脅迫的反應。

Research institutions in Xinjiang have also utilized sun-induced chlorophyll fluorescence to monitor plant responses to salt stress in Xinjiang and Central Asia.

標準化 SIFI 指標對八種代表性土地覆蓋類型的相對建模貢獻

Relative modeling contributions of the standardized SIFI indicator for eight representative land cover types.

SIF對早期脅迫的高度敏感性，使其成為監測鹽脅迫的有效工具，主要體現在以下方面：

·早期預警與精準管理：SIF可實現早期脅迫區域識別，幫助管理者及時調整灌溉、施用土壤改良劑或更換耐鹽品種，減輕產量損失。

·耐鹽品種選育：通過無損監測不同品種在鹽條件下的響應，可高效篩選出光合效率穩定的耐鹽材料，加速抗逆育種進程。

·科學研究與模型融合：SIF可與多源遙感數據及生態模型（如SCOPE、VISIT-SIF）結合，深化鹽脅迫下作物生理響應機制的認識，推動脅迫生理學發展。

The high sensitivity of SIF to early-stage stress makes it an effective tool for monitoring salt stress, mainly demonstrated in the following aspects:

·Early Warning and Precision Management: SIF enables the identification of stress-affected areas at an early stage, helping managers adjust irrigation, apply soil amendments, or switch to salt-tolerant varieties in a timely manner to mitigate yield losses.

·Breeding Salt-Tolerant Varieties: By non-destructively monitoring the responses of different varieties under saline conditions, photosynthetically efficient and salt-tolerant materials can be efficiently screened, accelerating the process of stress-resistant breeding.

·Scientific Research and Model Integration: SIF can be integrated with multi-source remote sensing data and ecological models (e.g., SCOPE, VISIT-SIF) to deepen the understanding of crop physiological responses under salt stress and advance stress physiology research.

目前，SIF的監測已從實驗室走向田間實際應用。

以我司推出的系列日光誘導葉綠素熒光監測系統為例，用戶無需自行搭建復雜模型與反演流程，即可直接獲取精準的SIF產額及光合作用效率數據。

我們提供多種部署形態：在線式監測系統可安裝于地面塔臺，實現無人值守、連續監測并自動回傳數據至云平臺；無人機載系統則支持靈活機動、高空間分辨率的田間巡測。無論哪種方式，都能幫助用戶快速、定量地評估鹽脅迫對植物光合功能的具體抑制程度，為精準農業提供穩定可靠的數據底層。

Currently, SIF monitoring has transitioned from the laboratory to practical field applications.

For instance, our company's series of sun-induced chlorophyll fluorescence monitoring systems allow users to directly obtain accurate SIF yield and photosynthetic efficiency data without the need to build complex models or inversion processes.

We offer multiple deployment options: online monitoring systems can be installed on ground-based towers for unattended, continuous monitoring with automatic data transmission to cloud platforms; UAV-mounted systems support flexible, high-spatial-resolution field surveys. Both approaches help users quickly and quantitatively assess the extent of salt stress-induced inhibition of plant photosynthetic function, providing a stable and reliable data foundation for precision agriculture.

ABN-SIF系列 / ABN-SIF Series

總之，日光誘導葉綠素熒光技術為鹽漬化監測與管理提供了強有力的工具。它早期、靈敏反映光合生理變化，支持精準農業、耐鹽育種與大尺度生態監測，為保障糧食安全提供重要科技支撐。

In summary, sun-induced chlorophyll fluorescence technology provides a powerful tool for monitoring and managing soil salinization. It offers early and sensitive detection of photosynthetic physiological changes, supports precision agriculture, salt-tolerant breeding, and large-scale ecological monitoring, and delivers crucial technological support for ensuring food security.

案例來源 / Sources ：

1. Du, R., Xiang, Y., Chen, J., Lu, X., Wu, Y., He, Y., Xiang, R., Zhang, Z., & Chen, Y. (2024). Potential of solar-induced chlorophyll fluorescence (SIF) to access long-term dynamics of soil salinity using OCO-2 satellite data and machine learning method. Geoderma, 444, 116855.

2. Cui, K., Ding, J., Wang, J., Tan, J., Han, L., & Li, J. (2025). Potential of solar-induced chlorophyll fluorescence for monitoring long-term dynamics of soil salinity in Central Asia the Xinjiang Region China. Frontiers in Plant Science, 16.