Abstract
Solar-induced chlorophyll fluorescence (SIF) is a hopeful indicator, which along with remote sensing, is used to measure the photosynthetic efficiency and gross primary production (GPP) of vegetation in regional terrestrial ecosystems. Studies have found a significant linear correlation between SIF and GPP in a variety of ecosystems. However, this relationship has mainly been established using SIF and GPP data derived from satellite remote sensing and continuous ground-based observations, respectively, which are difficult to accurately match. To overcome this, some studies have begun to use tower-based automatic observation instruments to study the changes of near-surface SIF and GPP. This study conducts continuous simultaneous observation of SIF, carbon flux, and meteorological factors on the forest canopy of a cork oak plantation during the growing season to explore how meteorological factors impact on canopy SIF and its relationship with GPP. This research found that the canopy SIF has obvious diurnal and day-to-day variations during the growing season but overall is relatively stable. Furthermore, SIF is greatly affected by incident radiation in different weather conditions and can change daily. Meteorological factors have a major role in the relationship between SIF and GPP; overall, the relationship shows a significant linear regression on the 30 min scale, but weakens when aggregating to the diurnal scale. Photosynthetically active radiation (PAR) drives SIF on a daily basis and changes the relationship between SIF and GPP on a seasonal timescale. As PAR increases, the daily slopes of the linear regressions between SIF and GPP decrease. On the 30 min timescale, both SIF and GPP increase with PAR until it reaches 1250 μmol·m−2·s−1; subsequently, SIF continues to increase while GPP decreases and they show opposite trends. Soil moisture and vapor pressure deficit influence SIF and GPP, respectively. Our findings demonstrate that meteorological factors affect the relationship between SIF and GPP, thereby enhancing the understanding of the mechanistic link between chlorophyll fluorescence and photosynthesis.
Highlights
Photosynthesis is one of the most important physiological activities in the existence of plant life; it is the source of all biological energy and is an important promoter of terrestrial ecosystem circulation [1,2]
Solar-induced chlorophyll fluorescence (SIF) captured on the plant canopy scale in the natural state through instruments mixed with a reflectance signal can be retrieved based on the Fraunhofer lines discriminator (FLD) method [9,10] and is used for estimating gross primary production (GPP)
We found that another part of the reason for the weakening of the correlation is that SIF and GPP have different responses to different meteorological factors
Summary
Photosynthesis is one of the most important physiological activities in the existence of plant life; it is the source of all biological energy and is an important promoter of terrestrial ecosystem circulation [1,2]. Light energy absorbed by chlorophyll pigments in photosystem II (PSII) in leaves dissipates by three main pathways: photochemistry (photochemical quenching, PQ), nonradioactively as heat (non-photochemical quenching, NPQ), and re-emitted as fluorescence [5]. It is the theoretical foundation of a unique relationship between ChlF and photochemistry efficiency as long as the NPQ is considered constant during the growing season while the pigment pool only varies slightly. SIF captured on the plant canopy scale in the natural state through instruments mixed with a reflectance signal can be retrieved based on the Fraunhofer lines discriminator (FLD) method [9,10] and is used for estimating GPP of terrestrial ecosystems, which provides favorable conditions for studying the spatial–
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