Ability of the Photochemical Reflectance Index to Track Light Use Efficiency for a Sub-Tropical Planted Coniferous Forest

Abstract

Light use efficiency (LUE) models are widely used to estimate gross primary productivity (GPP), a dominant component of the terrestrial carbon cycle. Their outputs are very sensitive to LUE. Proper determination of this parameter is a prerequisite for LUE models to simulate GPP at regional and global scales. This study was devoted to investigating the ability of the photochemical reflectance index (PRI) to track LUE variations for a sub-tropical planted coniferous forest in southern China using tower-based PRI and GPP measurements over the period from day 101 to 275 in 2013. Both half-hourly PRI and LUE exhibited detectable diurnal and seasonal variations, and decreased with increases of vapor pressure deficit (VPD), air temperature (Ta), and photosynthetically active radiation (PAR). Generally, PRI is able to capture diurnal and seasonal changes in LUE. However, correlations of PRI with LUE varied dramatically throughout the growing season. The correlation was the strongest (R 2 = 0.6427, p < 0.001) in July and the poorest in May. Over the entire growing season, PRI relates better to LUE under clear or partially cloudy skies (clearness index, CI > 0.3) with moderate to high VPD (>20 hPa) and high temperatures (>31˝C). Overall, we found that PRI is most sensitive to variations in LUE under stressed conditions, and the sensitivity decreases as the growing conditions become favorable when atmosphere water vapor, temperature and soil moisture are near the optimum conditions.

Linking In Situ Photochemical Reflectance Index Measurements With Mangrove Carbon Dynamics in a Subtropical Coastal Wetland

“…It is likely that the difference in daily PRI among seasons was partially caused by the seasonal changes in pigment pool size as frequently stated by previous studies (Gamon et al, 2016), but this long-term pigment regulatory mechanism may play a minor role in determining the seasonality of PRI in subtropical mangrove ecosystems. The weak seasonal PRI difference in mangrove forests is not in agreement with the hump-shaped seasonal patterns from previous studies in boreal evergreens (Soudani et al, 2014;Wong & Gamon, 2015), but it is comparable to other subtropical forest types (Zhang et al, 2015;Zhang et al, 2017). These contrasting findings are reasonable given that there was much smaller seasonal temperature difference in subtropical evergreens compared to boreal evergreens.…”

Potential of Photochemical Reflectance Index for Indicating Photochemistry and Light Use Efficiency in Leaves of European Beech and Norway Spruce Trees

“…Moreover, there are reports of difficulties with tracking LUE changes in drought-stressed vegetation that may originate from enhancement of respiration processes [74][75][76]. Probably due to interference with respiration we were also unable to distinguish between the effects of low temperature (HI-LT) versus the combined drought and high temperature stress (HI-HT3) using PRI in our dataset ( Figure 7A,B).…”

Relationship between Light Use Efficiency and Photochemical Reflectance Index Corrected Using a BRDF Model at a Subtropical Mixed Forest

“…Light use efficiency (LUE) is determined by environmental factors such as nutrients, moisture, and atmospheric temperature, resulting in differences in time and space in the photochemical reaction process. The photochemical reflectance index (PRI), based on remote sensing technology, provides the possibility to establish a link between changes in LUE and changes in the spectral characteristics of vegetation [9][10][11]. Some previous studies have shown that LUE is not a constant value in different ecosystems [12].…”

“…Using different fitting methods, the impact of VPD on the relationship between PRI and LUE was 34% and 38% [29]. Zhang et al research in subtropical coniferous forests showed that the correlation between PRI and LUE at half-hour and daily scales was 20% and 29%, respectively, and the correlation was small in suitable growth environments [10].The distribution of leaves in the vegetation canopy will affect the interception of solar radiation and the efficiency of light utilization. Lidar scans can more accurately retrieve vegetation canopy structural parameters [30].…”