Photochemical Reflectance Index (PRI) captures the ecohydrological sensitivity of a semi-arid mixed conifer forest
Creators
- 1. University of Utah
- 2. University of Arizona
- 3. Agricultural Research Service
Description
The Photochemical Reflectance Index (PRI) corresponds to the de-epoxidation state of the xanthophyll cycle and is one of the few pigment-based vegetation indices sensitive to rapid plant physiological responses. As such, new remotely-sensed PRI products present opportunities to study diurnal and seasonal processes in evergreen conifer forests, where complex vegetation dynamics are not well reflected by the small annual changes in chlorophyll content or leaf structure. Because PRI is tied explicitly to short and long term changes in xanthophyll pigments which are responsible for regulatig stress, this study characterized PRI in a semi-arid, sub-alpine mixed conifer forest, in order to assess its potential as a proxy for water stress by extension of its association with photoprotection. To determine the sensitivity of PRI to seasonal changes in ecohydrological variability and gross primary productivity, canopy spectral measurements were combined with eddy covariance flux and sap flow methods. Seasonally, there was a significant relationship between PRI and sap flow velocity (R2=0.56), and multiple linear regression analysis demonstrated the PRI response to dynamic water and energy limitations in this system. Although PRI was an effective indicator of stomatal response to ecohydrological constraints on a seasonal time scale, top-of-canopy leaf-level gas exchange, chlorophyll fluorescence, and hyperspectral reflectance measurements suggest that diurnal PRI saturates under conditions of severe light stress. This research indicates that remotely-sensed PRI has potential to fill spatial and temporal gaps in the ability to distinguish how water availability influences carbon dynamics of forested ecosystems.
Notes
Sap flow: Bigelow_sap_2018.csv
Half hourly data from day of year 186 - 304. Each column contains sap flow velocity in cm hr-1 from one sensor. Column name indicates tree ID and north or south side of tree. P in tree ID indicates species Pinus ponderosa. M in tree ID indicates species Pinus strobiformis. All trees are mature healthy individuals ~12-14m tall & ~75-105cm DBH.
Canopy Spectral Reflectance: Bigelow_NDVI_PRI_raw.csv
10 min data. Time stamp in format month/day/year hour:min. Data are raw sensor output. For complete description of data output see http://manuals.decagon.com/Manuals/14597_SRS_Web.pdf.
Leaf Data: Bigelow_Leaf_ChlF_gas_Hyperspec.csv
Composite file with leaf gas exchange (excel columns E-AC), chlorophyll fluorescence (excel columns AD-BL), and hyperspectral reflectance (350-2500nm) (excel columns BQ-CGP). Leaf gas exchange and ChlF parameter names correspond to standard licor-6800 output - see manual for parameter names and calculations. Gas exchange data are already corrected for leaf area.
Species code: PP = Pinus ponderosa, WP = Pinus strobiformis. Branch_ID indicates measurments from different branches on one tree of each species.
Suggested to not use data from rows: 21,22,26,27,42,43,49,51,33,34. Though data could be used depending on application (see column Licor_Notes).
Hyperspectral data for each row is an average of 2-3 spectra taken on same needles immediately following gas exchange/ChlF measurments.
Funding provided by: National Science Foundation
Crossref Funder Registry ID: http://dx.doi.org/10.13039/100000001
Award Number: EAR 1417101
Funding provided by: National Science Foundation
Crossref Funder Registry ID: http://dx.doi.org/10.13039/100000001
Award Number: EAR 1331408
Funding provided by: National Science Foundation
Crossref Funder Registry ID: http://dx.doi.org/10.13039/100000001
Award Number: EAR 1331906