Solar-Induced Chlorophyll Fluorescence Trends and Mechanisms in Different Ecosystems in Northeastern China

Abstract

Solar-induced chlorophyll fluorescence (SIF), when used as a proxy for plant photosynthesis, can provide an indication of the photosynthesis rate and has the potential to improve our understanding of carbon exchange mechanisms within an ecosystem. However, the relationships between SIF and vegetation indices (VIs) operating within different ecological contexts and the effect of other environmental factors on SIF remain unclear. This study focused on three ecosystems (cropland, forest, and grassland), with different ecological characteristics, located in Northeast China. These areas provide case studies where numerous relationships can be explored, including the correlations between the Orbiting Carbon Observatory-2 (OCO-2) SIF and MODIS products, meteorological factors, and the differences in the relationships between the three different ecosystems. Some interesting results and conclusions were obtained. First, in different ecosystems, the relationships between SIF and MODIS products show different correlations, whereby the enhanced vegetation index (EVI) has a close relationship with SIF in all the three ecosystems of forest, cropland, and grassland. Second, forest-type ecosystems appear to be sensitive to changes in daily temperature, whereas cropland and grassland areas respond more closely to changes in previous 16-day daily minimum temperature. Compared with forest and cropland areas, grasslands were more sensitive to precipitation (although the R2 value was small). Third, different ecosystems have different mechanisms of photosynthesis. Hence, we suggest that it is better to use SIF in areas exhibiting different ecological characteristics, and different models should be employed while simulating SIF.

A Machine Learning Approach for Mapping Chlorophyll Fluorescence at Inland Wetlands

“…The research on a time series of combined optical Sentinel-2 and field remote sensing data led to providing maps of chlorophyll fluorescence over wetlands in a large area. So far, several studies have documented the potential of remote sensing data to map chlorophyll fluorescence [13,16,79]. Whilst Sinha et al [18] used medium-resolution remote sensing imagery for estimating seasonal fluorescence dynamics at deciduous forests, we mapped the areas difficult to access with high water-level fluctuations.…”

“…This serves as a proxy for plant photosynthesis [11,12]. Nevertheless, recent studies on conventional ChF retrieval methods in terrestrial ecosystems are challenged by vegetation heterogeneity, seasonal dynamics, and variations in the physical environment among different ecosystems [13][14][15][16]. Algorithms attempting to extract patterns from satellite data are still being developed for retrieving and mapping ChF [17][18][19].…”

Temporal Variation in Tower-Based Solar-Induced Chlorophyll Fluorescence and Its Environmental Response in a Chinese Cork Oak Plantation

“…Canopy structures, such as LAI and the leaf angle, not only determine the multiple scattering and absorption of radiation and fluorescence, they also affect the zenith and the azimuth angle [49]. According to previous studies on ecosystem water and the carbon flux constraints based on SIF, the simpler the canopy structure of vegetation, the higher the accuracy of the simulated value [50,51]. The canopies with complex structures are more likely to be affected by the sunlight observation geometry [52].…”