Estimation of photosynthetic dynamics in forests from daily measured fluorescence and PRI data with adjustment for canopy shadow fraction
Kováč, Daniel (Czech Academy of Sciences. Global Change Research Institute)
Novotný, Jan (Czech Academy of Sciences. Global Change Research Institute)
Šigut, Ladislav (Czech Academy of Sciences. Global Change Research Institute)
Ač, Alexander (Czech Academy of Sciences. Global Change Research Institute)
Peñuelas, Josep (Centre de Recerca Ecològica i d'Aplicacions Forestals)
Grace, John (University of Edinburgh. School of GeoSciences)
Urban, Otmar (Czech Academy of Sciences. Global Change Research Institute)

Date:	2023
Abstract:	We conducted year-long measurements of the photochemical reflectance index (PRI) and solar-induced fluorescence in the O2A oxygen band (SIFA) at a Norway spruce forest and a European beech forest to study relationships of these remote sensing variables to photosynthesis by trees in grown forest stands. Measured PRI and SIFA values were linked to changes in forest gross primary productivity (GPP) and light-use efficiency (LUE). Changes in the shadow fraction (αS) within tree crowns influenced PRI and fluorescence signals. In the spruce forest, the quantum yield of SIFA (FYSIFA) decreased around midday together with photosynthesis and GPP. Such decreases in FYSIFA were accompanied by an increase in the αS. In the beech forest, we detected an increase in FYSIFA together with a decrease in αS in the afternoon hours. The overall sensitivity of PRI to LUE was variable according to the season, presumably influenced by complex changes in photosynthetic pigments. PRI and FYSIFA showed weak correlations with canopy LUE; however, when considered together, the correlation was strengthened (R2 was 0. 63 and 0. 34 in spruce and beech forest, respectively). Our model predicting LUE dynamics includes a diurnal minimum of PRI and canopy αS to make allowances for seasonal changes in photosynthetic pigments and for diurnal variability of the shadow fraction in forests. The incorporation of these correcting factors allowed us to estimate LUE at R2 = 0. 68 (spruce) and 0. 53 (beech). The modeling equations appeared sensitive to the absorbed photosynthetically active radiation (APAR), but less sensitive to the GPP of these forests. Substituting pigments correction with introducing differential PRI (ΔPRI) into the model did not significantly improve the LUE estimation across the season. Our results show that the joint use of PRI and fluorescence improves LUE and GPP estimation accuracy in both daily and seasonal observations.
Grants:	Agencia Estatal de Investigación PID2019-110521GB-I00
Rights:	Aquest document està subjecte a una llicència d'ús Creative Commons. Es permet la reproducció total o parcial, la distribució, i la comunicació pública de l'obra, sempre que no sigui amb finalitats comercials, i sempre que es reconegui l'autoria de l'obra original. No es permet la creació d'obres derivades.
Language:	Anglès
Document:	Article ; recerca ; Versió acceptada per publicar
Subject:	3-FLD ; Daily dynamics ; Fluorescence ; LiDAR ; Photochemical reflectance index ; Shadow fraction
Published in:	Science of the total environment, Vol. 898 (Nov. 2023) , art. 166386, ISSN 1879-1026

DOI: 10.1016/j.scitotenv.2023.166386

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Research literature > UAB research groups literature > Research Centres and Groups (research output) > Experimental sciences > CREAF (Centre de Recerca Ecològica i d'Aplicacions Forestals)
Articles > Research articles
Articles > Published articles