{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,16]],"date-time":"2026-03-16T23:01:40Z","timestamp":1773702100133,"version":"3.50.1"},"reference-count":46,"publisher":"MDPI AG","issue":"6","license":[{"start":{"date-parts":[[2025,3,9]],"date-time":"2025-03-09T00:00:00Z","timestamp":1741478400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"National Natural Science Foundation of China","award":["42071328"],"award-info":[{"award-number":["42071328"]}]},{"name":"National Natural Science Foundation of China","award":["41901293"],"award-info":[{"award-number":["41901293"]}]},{"name":"National Natural Science Foundation of China","award":["24520212452021125"],"award-info":[{"award-number":["24520212452021125"]}]},{"name":"Chinese Universities Scientific Fund","award":["42071328"],"award-info":[{"award-number":["42071328"]}]},{"name":"Chinese Universities Scientific Fund","award":["41901293"],"award-info":[{"award-number":["41901293"]}]},{"name":"Chinese Universities Scientific Fund","award":["24520212452021125"],"award-info":[{"award-number":["24520212452021125"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>The fraction of open Photosystem II (PSII) reaction centers (qL) is critical for connecting broadband PSII fluorescence (ChlFPSII) with the actual electron transport from PSII to Photosystem I. Accurately estimating qL is fundamental for determining ChlFPSII, which, in turn, is vital for mechanistically estimating the actual electron transport rate and photosynthetic CO2 assimilation. Chlorophyll fluorescence provides direct physiological insights, offering a robust foundation for qL estimation. However, uncertainties in the ChlFPSII\u2013qL relationship across different plant functional types (PFTs) limit its broader application at large spatial scales. To address this issue, we developed a leaf-level instrument capable of simultaneously measuring actively and passively induced chlorophyll fluorescence. Using this system, we measured light response, CO2 response, and temperature response curves across 52 species representing seven PFTs. Our findings reveal the following: (1) a strong linear correlation between ChlFPSII derived from passively induced fluorescence and that from actively induced fluorescence (R2 = 0.85), and (2) while the parameters of the ChlFPSII\u2013qL relationship varied among PFTs, ChlFPSII reliably modeled qL within each PFT, with the R2 ranging from 0.85 to 0.96. This study establishes quantitative ChlFPSII\u2013qL relationships for various PFTs by utilizing passively induced fluorescence to calculate ChlFPSII. The results demonstrate the potential for remotely sensed chlorophyll fluorescence data to estimate qL and strengthen the use of fluorescence-based approaches for mechanistic GPP estimation at large spatial scales.<\/jats:p>","DOI":"10.3390\/s25061700","type":"journal-article","created":{"date-parts":[[2025,3,10]],"date-time":"2025-03-10T05:46:52Z","timestamp":1741585612000},"page":"1700","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":3,"title":["Application of Simultaneous Active and Passive Fluorescence Observations: Extending a Fluorescence-Based qL Estimation Model"],"prefix":"10.3390","volume":"25","author":[{"given":"Chenhui","family":"Guo","sequence":"first","affiliation":[{"name":"College of Natural Resources and Environment, Northwest A&F University, Yangling 712100, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-5902-6043","authenticated-orcid":false,"given":"Zhunqiao","family":"Liu","sequence":"additional","affiliation":[{"name":"State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Northwest A&F University, Yangling 712100, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Xiaoliang","family":"Lu","sequence":"additional","affiliation":[{"name":"State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Northwest A&F University, Yangling 712100, China"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2025,3,9]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"4065","DOI":"10.1093\/jxb\/eru191","article-title":"Linking chlorophyll a fluorescence to photosynthesis for remote sensing applications: Mechanisms and challenges","volume":"65","author":"Atherton","year":"2014","journal-title":"J. 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