The divergence of micrometeorology sensitivity leads to changes in GPP/SIF between cork oak and poplar

Abstract

The observation of solar-induced chlorophyll fluorescence (SIF) signals on a spaceborne platform provides a new idea for estimating and monitoring the gross primary production (GPP) of terrestrial ecosystems at the regional scale. To improve the accuracy of remote sensing SIF signals to estimate GPP, the combination of ground tower-based continuous SIF signals with GPP to explore the mechanical connection in different ecosystems is needed. Based on continuous ground observations, the discrepancy of the links between SIF and GPP and the response to micrometeorology factors of two temperate deciduous broadleaf plantations was explored. The nonlinear relationship of SIF and GPP on the 30 min timescale transformed into a linear correlation with aggregation. With the increase in SIF, GPP gradually saturates and even declines in cork oak. We found SIF “promotion” by using intense incident radiation in cork oak and GPP “depression” or saturation in both species. GPP is more sensitive to instantaneous stresses such as intense radiation imposed high air temperature (Ta) in the midday/afternoon, and the stress threshold of cork oak is lower. We used GPP/SIF as a metric for the relationship, which is significantly higher in poplar, and found GPP/SIF of both species decrease with increasing photosynthetically active radiation (PAR). Since the difference in the amplitude of SIF between tree species was not prominent, the diversity of GPP/SIF performance was mainly caused by the divergence of GPP. The GPP/SIF of cork oak continues to decrease with increasing vapor pressure deficit (VPD), indicating that the relationship between SIF and GPP has a strong daily pattern in the constraint of micrometeorology factors. Our results show that characterizing the impact of micrometeorological conditions on the SIF-GPP relationship in a specific ecosystem is of great significance for the reliable estimation of GPP from remote sensing.