Spectral Characteristics in Tulip Poplar Trees

1. Leaf-level variations in the bio-physical and high spectral resolution reflectance properties associated with light environment in tulip poplar trees Matthew Wiener Research & Discover August 7, 2009

2. Objectives • Compile data set for Smithsonian Environmental Research Center (May 2009) 2) Examine patterns in Light Use Efficiency (LUE) within a tulip poplar canopy -Hypothesis: LUE will be greater in sunlit upper portions of the canopy 3) Identify spectral and biophysical parameters that are useful in monitoring LUE -Hypothesis: The PRI, which is based upon xanthophyll activity, will be effective at monitoring LUE

3. Background • LUE Concept: Carbon assimilation by plants is a function of photosynthetically active radiation (PAR) • LUE=Amax/PAR • LUE is greatest in early morning when water is available • Stress increases over the course of a day • Exaggerates the degree to which excess light is harmful • Energy dissipation occurs through the xanthophyll cycle and chlorophyll fluorescence • LUE indices are generally based upon these forms of biochemical protection

4. Background • LUE has been successfully tracked using the photochemical reflectance index (PRI)

5. Background • The PRI employs a narrow spectral band centered at physiologically active response at 531 nm 531 nm

6. Background • The PRI employs a narrow spectral band centered at physiologically active response at 531 nm • And a reflectance band insensitive to the xanthophyll signal at 570 nm 531 nm 570 nm

7. Background • The PRI employs a narrow spectral band centered at physiologically active response at 531 nm • And a reflectance band insensitive to the xanthophyll signal at 570 nm 531 nm 570 nm Relationships between LUE and Fv/Fm (dark-adapted fluorescence) and other parameters have also been observed!

8. Methods/DataCollection Smithsonian Env. Research Center (SERC) site is located in Edgewater, MD. Contains a 2 km continuous mature poplar dominated mixed forest with a maximum height of 40 meters. Leaves collected from 4 locations on 2 mature Tulip Poplar trees. - Upper Canopy, Sunlit - Upper Canopy, Shaded - Lower Canopy, Sunlit - Lower Canopy, Shaded Leaves were analyzed in the man-basket with a spectroradiometer (Analytical Spectral Devices, Inc., Boulder, Colorado). Leaves were scanned in the SERC lab space using a Li-6400 photosynthesis system (Li-Cor Biosciences, Lincoln, Nebraska) to measure photosynthetic and fluorescence parameters Me

9. Site 1 (Tree #1) Site 2 (Tree #2)

10. Results: LUE – SERC May 2009 Significant differences in LUE due to TIME atSite 1(p<0.005) but notSite 2(p=0.898)

11. LUE – SERC May 2009 No differences in LUE due to LIGHT ENVIRONMENT atSite 1(p=0.564) orSite 2(p=0.170)

12. LUE - SERC May 2009 No differences in LUE due to CANOPY POSITION atSite 1(p=0.492)orSite 2(p=0.624)

13. Spectral Indices PRI 1 r=0.0224

14. Spectral Indices G035 r=0.2685

15. Fluorescence Parameters Fm r=0.3863

16. Conclusions Conclusions • LUE does not vary significantly within tulip poplar canopies by light environment (sun vs. shade) nor upper vs. lower location of the foliage • Time does have a significant effect • Spectral indices are less effective than photosynthetic parameters for tracking LUE • More work is needed so remote sensing tools can properly monitor LUE within forest canopies

17. NASA Relevance • With further research, NASA sponsored satellite imaging systems can be used to monitor LUE across forest landscapes • This will allow more accurate assessments of vegetation stress over temporal and geographic scales • It can also indicate “efficient” plant species which ideally will sequester carbon more rapidly and under a greater range of environmental conditions

18. Acknowledgements I would like to thank… Goddard Space Flight Center Betsy Middleton Petya Campbell Yen-Ben Cheng Larry Corp Fred Huemmrich - and - The Research & Discover Program George Hurt Clara Kustra Barry Rock