Nitrogen and Phosphorus Effect on Sun-Induced Fluorescence and Gross Primary Productivity in Mediterranean Grassland

Abstract

Sun-Induced fluorescence at 760 nm (F760) is increasingly being used to predict gross primary production (GPP) through light use efficiency (LUE) modeling, even though the mechanistic processes that link the two are not well understood. We analyzed the effect of nitrogen (N) and phosphorous (P) availability on the processes that link GPP and F760 in a Mediterranean grassland manipulated with nutrient addition. To do so, we used a combination of process-based modeling with Soil-Canopy Observation of Photosynthesis and Energy (SCOPE), and statistical analyses such as path modeling. With this study, we uncover the mechanisms that link the fertilization-driven changes in canopy nitrogen concentration (N%) to the observed changes in F760 and GPP. N addition changed plant community structure and increased canopy chlorophyll content, which jointly led to changes in photosynthetic active radiation (APAR), ultimately affecting both GPP and F760. Changes in the abundance of graminoids, (%graminoids) driven by N addition led to changes in structural properties of the canopy such as leaf angle distribution, that ultimately influenced observed F760 by controlling the escape probability of F760 (Fesc). In particular, we found a change in GPP–F760 relationship between the first and the second year of the experiment that was largely driven by the effect of plant type composition on Fesc, whose best predictor is %graminoids. The P addition led to a statistically significant increase on light use efficiency of fluorescence emission (LUEf), in particular in plots also with N addition, consistent with leaf level studies. The N addition induced changes in the biophysical properties of the canopy that led to a trade-off between surface temperature (Ts), which decreased, and F760 at leaf scale (F760leaf,fw), which increased. We found that Ts is an important predictor of the light use efficiency of photosynthesis, indicating the importance of Ts in LUE modeling approaches to predict GPP.

NIRvP: a robust structural proxy for sun-induced chlorophyll fluorescence and photosynthesis across scales

“…Site data. We used previously published data from a total of six sites located in South Korea (rice) 14 , China (corn 1) 65 , France (wheat) 66 , Spain (natural grassland) 16,67,68 resolutions. An overview of all site-level and larger scale SIF datasets including information on the retrieval algorithm used is given in Table M1 below.…”

Review of Top-of-Canopy Sun-Induced Fluorescence (SIF) Studies from Ground, UAV, Airborne to Spaceborne Observations

“…The outcome showed that nutrient implementation made changes in the abundance of plant forms and biochemistry of the canopy structure, which ultimately impacts the SIF 760 and GPP relationship. A similar kind of work was conducted by Martini et al [95] to show the SIF 760 and GPP relationship under nitrogen (N) and phosphorus (P) treatment conditions over the Mediterranean grassland. In another study, Wohlfahrt et al [96] investigated the SIF-GPP relationship under short-term intense heatwave conditions over the Mediterranean pine forest.…”

Analysis of designs used in monitoring crop growth based on remote sensing methods

“…Importantly, fluorescence ground measurements can be scaled up from the leaf to the canopy level (Moya et al, 2004), and the resulting measurements can be used to obtain chlorophyll fluorescence values and to correlate these with environmental conditions (for example, photosynthetic active radiation, or gas exchange) (Moya et al, 2006) as well as to detect plant stress. Several studies have established the existence of a significant relationship between SIF and various environmental stressors, including plant water stress (Evain et al, 2002), extreme temperature (Ac et al, 2015), nitrogen (N) and phosphorous (P) treatments (Kebanian et al, 1999;Martini et al, 2019;Migliavaca et al, 2017), ozone stress (Meroni et al, 2008), and stress induced by herbicide treatment (Van Rensen, 1989). Ground measurements are also able to estimate GPP (Yang et al, 2015;Wolfhart et al, 2018).…”