Mechanistic insights on canopy photosynthesis estimation in a temperate evergreen needleleaf forest using sun-induced chlorophyll fluorescence and relevant vegetation indices
Abstract
Northern hemisphere evergreen needleleaf forests (ENF) assimilate a significant amount of global atmospheric CO2 but quantifying their gross primary production (GPP) remains a challenge. Recently, solar-induced chlorophyll fluorescence (SIF), chlorophyll/carotenoid index (CCI) and near-infrared reflectance of vegetation (NIRv) were reported to be useful tools to estimate GPP in ENF. However, the reported good performance of these approaches in ENF still have not been fully understood. Here, we present continuous in-situ observations of canopy-level SIF, GPP, CCI and NIRv in a temperate ENF across two growing season. Based on mechanistic considerations, we also propose CCI × NIRv × PAR as novel index for tracking GPP. We found that SIF showed overall good performance to track GPP (R2 = 0.80, rRMSE = 27 %, daily). The novel index had strong linear correlation with GPP at seasonal time scales (R2 = 0.83, rRMSE = 25 %). On the other hand, we found that NIRv × PAR could not track the seasonal dynamics of GPP well due to its poor performance during winter (R2 = 0.46, rRMSE = 35 %, daily). CCI only explained 53% of variance in GPP (rRMSE = 45 %, daily), but CCI × PAR had a much improved correlation with GPP (R2 = 0.8, rRMSE = 28%, daily). Our findings highlight that CCI could track LUE well and NIRv could improve the CCI-LUE relationship because NIRv is partially capturing the response of LUE to diffuse fraction. In addition, we confirmed that our novel index could track SIF well as CCI had a linear relationship with the physiological component of SIF, ΦF, and NIRv is known to correspond to the structure-radiation component of SIF. These results will be useful for improving remote sensing based GPP estimation in ENF.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMB006.0016K
- Keywords:
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- 0426 Biosphere/atmosphere interactions;
- BIOGEOSCIENCES;
- 0428 Carbon cycling;
- BIOGEOSCIENCES;
- 0452 Instruments and techniques;
- BIOGEOSCIENCES;
- 0476 Plant ecology;
- BIOGEOSCIENCES