Standardized methods for. canopies using a ceptometer.

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1 Standardized methods for measuring intercepted PAR in canopies using a ceptometer. Dr. Mari-Vaughn V. Johnson USDA-ARS - Grassland, Soil, and Water Research Lab Temple, Texas Collaborators: Dr. Jim Kiniry (USDA-ARS) Dr. Byron Burson (Texas A&M University)

2 Introduction Dr. Mari-Vaughn V. Johnson Ph.D., 2007: Texas A&M University Research Agronomist, 2007-present: USDA- ARS at Grassland, Soil, and Water Research Lab, Temple, Texas Ongoing Research: Quantifying and modeling plant physiological Qua y ga d ode gpa p ysoogca process in biofuel production systems and western rangeland systems.

3 Definitions PAR: photosynthetically active radiation fipar: fraction of intercepted PAR fapar: fraction of absorbed PAR

4 Leaf Area Index (LAI) LAI: one sided leaf area per unit ground area

5 Why measure LAI? LAI is related to photosynthesis and primary production (biomass) LAI influences how light moves through a canopy LAI influences microclimate LAI can be used as an indicator of canopy health or development

6 Who is interested in LAI? Extension Agents Range Scientists Agronomists Ecologists Producers Crop Breeders

7 An exemplary model: ALMANAC Radiation Use Efficiency (RUE) is the slope of above ground dry biomass as a function of cumulative FiPAR RUE allows prediction of plant growth and biomass production

8 Determining LAI Non-destructive methods: Satellite Sae eremote oesensing Hemispherical photography LAI 2000/ LAI 2200 Light bar/lp-80 Ceptometer

9 LAI Destructive Sampling Harvest leaves a given ground area, often 1 m 2 Physically measure surface area with optical meter

10 Advantages of Non-Destructive Sampling Less time consuming Less unwieldy Repeatable Less disturbance

11 AccuPAR LP-80 Ceptometer Measures Fraction of Intercepted Photosynthetically Active Radiation (FiPAR) Can calculate LAI

13 What parameters are needed to calculate LAI with the ceptometer? Zenith angle (ψ) Time and location latitude and longitude Canopy extinction coefficient (G) Calculate from leaf angle distribution (χ) = 1 for most canopies Canopy transmission coefficient (τ) Estimate from fisheye image Use ceptometer to measure directly

14 Accurate LAI and biomass predictions dependd on accurate FIPAR inputs Sources of bias: Time of day Self-shading Over/Under sampling Different ceptometer deployment methods

Experimental Design Field Site 1: Buffelgrass:

Gustine, TX 1 rhizomatous type: Miscanthus 1

15 Experimental Design Field Site 1: Buffelgrass: College Station, TX 2 rhizomatous types: Nueces and Llano 2 bunchgrass types: Common and Frio Field Site 2: Switchgrass and Miscanthus: Gustine, TX 1 rhizomatous type: Miscanthus 1 bunchgrass type: Alamo switchgrass 2 nutrient level treatments

16 Miscanthus rhizomes Switchgrass roots Buffelgrass invasion Buffelgrass forage

17 Field Site 1: Buffelgrass Field Site 2: Switchgrass and Miscanthus

18 Three methods of deployment 1 m 1 m Plant Method Transect Method Cross Method

19 Ground truthing FIPAR measurements

20 Comparing Mean FiPAR Results by Method LP-80 Deployment Method Species/Cultivar Plant Transect Cross Miscanthus Control Switchgrass Control Frio Llano Common Nueces Miscanthus Effluent Switchgrass Effluent

21 Buffelgrass Results: Repeated Measures ANOVA(PROC MIXED) Deployment Method Effect (F=21.42; P < ) Multiple l Comparisons Results Plant Method = Transect Method (P = 0.28) Plant Method < Cross Method (P = 0.01) Transect Method < Cross Method (P < 0.01)

22 Miscanthus and Switchgrass Effluent Treatment

23 Switchgrass/Miscanthus Results: Repeated Measures ANOVA(PROC MIXED) Main effects: Deployment Method (F = 22.20; P < 0.001) Effluent Effects (F = ; P < 0.001) Interaction effects: Species X Effluent (F = 11.07; P = 0.02) Method X Effluent (F = 6.32; P = 0.02)

24 Mean FiPAR and LAI Results by Method Leaf Area Index LP-80 Deployment Method Species/Cultivar Max Mean Plant Transect Cross Miscanthus Control Switchgrass Control Miscanthus Effluent Switchgrass Effluent

25 Bonferroni Adjustments to LSMs Insignificant interactions when comparing FIPAR: Plant Method VS Transect Method in control plots Plant Method VS Transect Method in effluent plots Plant Method VS Cross Method in effluent plots Transect Method VS Cross Method in effluent plots Conclusion: Plant and Transect Methods are comparable; Cross Method is only comparable at high LAI (effluent plots)

26 Modeling with FIPAR: FiPAR is a function of a canopy s LAI and light extinction coefficient (k) Using Beer s law, FiPAR = 1.0 exp(-k*lai)

27 Beer s Law to Predict k Plant Method Transect Method Cross Method Species/Cultivar Mean LAI fipar k fipar k fipar k Miscanthus Control Switch Control Frio Llano Common Nueces Miscanthus Effluent Switch Effluent

28 Conclusion: 1 m 1 m Plant Method Transect Method Cross Method Plant and transect FiPAR collection methods are comparable in these agronomic settings Cross method showed the highest tendency to bias predictions, particularly at low LAI

29 Future Directions: Determine minimum number of samples that make a method work Explore the precision and accuracy of the three methods under other plant canopies Determine if there is a minimum LAI, after which method is not a significant bias Devise another method to explore, perhaps a transect method with fewer points of measurement

30 Thank You.Any Questions?

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