Publication Date:
2024-03-18
Description:
Various environmental variables drive gross primary productivity (GPP) and light use efficiency (LUE) of forest ecosystems. However, due to their intertwined nature and the complexity of measuring absorbed photosynthetically active radiation (APAR) of forest canopies, the assessment of LUE and the importance of its environmental drivers are difficult. Here, we present a unique combination of measurements during the 2021 growing season including eddy covariance derived GPP, sap flow, Sentinel‐2 derived canopy chlorophyll content and in situ measured APAR. The importance of environmental variables for GPP models is quantified with state‐of‐the‐art machine learning techniques. A special focus is put on photosynthesis‐limiting conditions, which are identified by a comparison of GPP and sap flow hysteretic responses to Vapor pressure deficit (VPD) and APAR. Results demonstrate that (a) LUE of the canopy's green part was on average 4.0% ± 2.3%, (b) canopy chlorophyll content as a seasonal variable for photosynthetic capacity was important for GPP predictions, and (c) on days with high VPD, tree‐scale sap flow and ecosystem‐scale GPP both shift to a clockwise hysteretic response to APAR. We demonstrate that the onset of such a clockwise hysteretic pattern of sap flow to APAR is a good indicator of stomatal closure related to water‐limiting conditions at the ecosystem‐scale.
Description:
Plain Language Summary:
The efficiency by which a forest uses sunlight to perform photosynthesis is an important feature for climate and ecosystem modeling. However, the light that is actually captured by forests and is useable for photosynthesis is difficult to assess. Here, we show a sophisticated approach to estimate the light use efficiency of a spruce forest in Germany and analyze environmental influences on it and on photosynthesis. Our results indicate that about 4% of the light useable for photosynthesis was actually used by the forest during the 2021 growing season and that seasonal variations of chlorophyll in the canopy are a good indicator for carbon capture.
Description:
Key Points:
A seasonal variable such as canopy chlorophyll content was useful to predict gross primary productivity with machine learning models.
A clockwise hysteretic pattern of sap flow to radiation is a good indicator of water‐related stomatal closure.
The light use efficiency of green parts of a spruce forest was 4.0% with a standard deviation of 2.3% during the 2021 growing season.
Description:
RWTH Aachen University
http://dx.doi.org/10.13039/501100007210
Description:
University of Alberta
http://dx.doi.org/10.13039/501100000190
Description:
Excellence Strategy of the Federal Government and the Länder
Description:
Waldklimafonds
http://dx.doi.org/10.13039/501100010297
Description:
German Federal Ministry of Food and Agriculture
Description:
German Federal Ministry for the Environment, Nature Conservation, Nuclear Safety and Consumer Protection
Description:
TERENO project
Description:
Helmholtz research infrastructure Modular Observation Solutions for Earth Systems
Description:
http://doi.org/10.5281/zenodo.7014604
Description:
https://www.opengeodata.nrw.de/produkte/geobasis/hm/3dm_l_las/3dm_l_las/
Description:
https://scihub.copernicus.eu/
Keywords:
ddc:634.9
;
photosynthetically active radiation
;
canopy chlorophyll content
;
hysteresis
;
sap flow
;
variable importance
;
Picea abies
Language:
English
Type:
doc-type:article
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