Disconnect between SIF and tree-level physiology: Limitations of SIF as a proxy for GPP?
Abstract
The terrestrial biosphere is a crucial sink for anthropogenic carbon (C) emissions to the atmosphere, but is also the source of the largest uncertainties in estimated global C budgets. In 2017, the Forested Optical Reference for Evaluating Sensor Technology (FOREST) site was established in suburban Maryland, at the National Institute of Standards and Technology (NIST), as a test-bed for developing a suite of complementary instrumentation for characterizing above- and belowground C fluxes. Among these, we have refined a spectrometer deployment for measuring solar-induced fluorescence (SIF), which, as a proxy for photosynthesis, shows promise for constraining global estimates of gross primary productivity. Nonetheless, published SIF retrievals span two orders of magnitude, illustrating an opportunity for improved characterization of instrument noise, detector calibrations and limitations, and signal sensitivity to light conditions, fill factor, viewing geometry, and atmospheric effects. On time scales of hours to days, we do not observe strong correlations between SIF and either leaf-level metrics of photosynthesis or whole-tree integrated C assimilation using sap flux sensors. For example, in tulip poplar we experimentally reducedstomatal conductance (-87.1 ± 0.02%) and C assimilation (-80.1 ± 0.90%)and saw no concurrent changes in SIF. Further work toward directly linking SIF retrievals to C exchange is being performed using leaf-level gas exchange measurements, high performance liquid chromatography quantification of leaf pigment concentrations, an extensive suite of ground measurements, and integration with remote sensing driven models.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.A53I..19H
- Keywords:
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- 3322 Land/atmosphere interactions;
- ATMOSPHERIC PROCESSES;
- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCES;
- 0428 Carbon cycling;
- BIOGEOSCIENCES;
- 0480 Remote sensing;
- BIOGEOSCIENCES