|Miao, Guofang - University Of Illinois|
|Guan, Kaiyu - University Of Illinois|
|Yang, Xi - University Of Virginia|
|Berry, Joseph - Carnegie Institute - Stanford|
|Delucia, Evan - University Of Illinois|
|Wu, Jin - Brookhaven National Laboratory|
|Moore, Caitlin - University Of Illinois|
|Meacham, Katharine - University Of Illinois|
|Cai, Yaping - University Of Illinois|
|Peng, Bin - University Of Illinois|
|Kimm, Hyungsuk - University Of Illinois|
|Masters, Michael - University Of Illinois|
Submitted to: Journal of Geophysical Research-Biogeosciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/29/2018
Publication Date: 3/14/2018
Citation: Miao, G., Guan, K., Yang, X., Bernacchi, C.J., Berry, J.A., DeLucia, E., Wu, J., Moore, C.E., Meacham, K., Cai, Y., Peng, B., Kimm, H., Masters, M.D. 2018. Sun-induced chlorophyll fluorescence, photosynthesis, and light use efficiency of a soybean field from seasonally continuous measurements. Journal of Geophysical Research-Biogeosciences. 123(2):610-623.
Interpretive Summary: Photosynthesis at a leaf scale is relatively easy to measure, but at the scale of a whole canopy there exist many challenges. The most direct means for measuring canopy photosynthesis include placing a section of a field into an enclosure or using very expensive, bulky, and time-consuming sensors. These techniques are very disruptive to plant functioning under normal field conditions. Newer techniques are being developed that rely on remote sensing. These methods are much preferred because they can be done from above a plant canopy ranging from slightly above the plants to satellite observation from space. One such technique, referred to as Solar Induced Fluorescence (SIF), is a measure of how efficient plants are at using light. While this method is becoming more popular, there is currently a lot of uncertainty regarding what is actually measured. To help understand how this technique works, we designed an experiment whereby we measured photosynthesis in soybean using a technique referred to as eddy covariance. This measurement technique is very accurate but requires significant investments of time and money to get an average measurement from a whole field. We coupled this measurement with SIF to better understand the relationship between the eddy covariance and SIF signals over multiple growth stages and environmental conditions over a whole growing season. The results provide new insights into how SIF can be used to measure canopy photosynthesis over very diverse conditions.
Technical Abstract: Recent development of sun-induced chlorophyll fluorescence (SIF) technology is stimulating studies to remotely approximate canopy photosynthesis (measured as gross primary production, GPP). While multiple applications have advanced the empirical relationship between GPP and SIF, mechanistic understanding of this relationship is still limited. GPP:SIF relationship, using the standard light use efficiency framework, is determined by absorbed photosynthetically active radiation (APAR) and the relationship between photosynthetic light use efficiency (LUE) and fluorescence yield (SIFy). While previous studies have found that APAR is the dominant factor of the GPP:SIF relationship, the LUE:SIFy relationship remains unclear. For a better understanding of the LUE:SIFy relationship, we deployed a ground-based system (FluoSpec2), with an eddy-covariance flux tower at a soybean field in the Midwestern U.S. during the 2016 growing season to collect SIF and GPP data simultaneously. With the measurements categorized by plant growth stages, light conditions, and time scales, we confirmed that a strong positive GPP:SIF relationship was dominated by an even stronger linear SIF:APAR relationship. By normalizing both GPP and SIF by APAR, we found that under sunny conditions our soybean field exhibited a clear positive SIFy:APAR relationship and a weak negative LUE:SIFy relationship, opposite to the positive LUE:SIFy relationship reported previously in other ecosystems. Our study provides a first continuous SIF record over multiple growth stages for agricultural systems and reveals a distinctive pattern related to the LUE:SIFy relationship compared with previous work. The observed positive relationship of SIFy:APAR at the soybean site provides new insights of the previous understanding on the SIF’s physiological implications.