Vegetation

Mayer: "Nature has put itself the problem of how to catch in flight light streaming to the Earth and to store the most elusive of all powers in rigid form. The plants take in one form of power, light; and produce another power, chemical difference."

Three factors determine canopy reflectance 1. Spectral scattering/absorbing properties of canopy components. (leaves, stems, flowers, fruit, soil, etc.) 2. Canopy architecture. (above-ground biomass; leaf area index; arrangement of foliage in x,y,z,q,f space – for example, are all leaves vertical and located in one layer – or perhaps they are arranged in space like the area on a sphere; etc.) 3. Directions of illumination and view. (Is the sun the only significant source – or does aerosol- or Rayleigh-scattered light provide hemispherical illumination; is direction of view toward the hot spot or nadir or …)

Three factors determine canopy reflectance 1. Spectral scattering/absorbing properties of canopy components. (leaves, stems, flowers, fruit, soil, etc.) Reflection: Volume scattering from leaf interior (is diffuse & pigment absorption apparent) + Surface reflection (is often fairly specular & displays no evidence of pigments) The Leaf Transmission: Volume scattering from leaf interior (is diffuse & pigment absorption apparent)

The Leaf

Chloroplasts “sieve effect”

Chlorophyll

Carotenes

Light Harvesting Complex II The chlorophyll binding proteins are bound into the thylakoid membranes of the chloroplast and organised into photosystems I and II. These membrane bound supercomplexes of pigment binding proteins are further associated with electron transport components: Within the pigment binding proteins the chlorophylls and carotenoids are specifically bound in defined positions and orientations (remember the comments about the ’triplet valve’?); this organisation allows the excitation energy to move from chl b to chl a, and then between the chla s. The pigment-protein complexes asscociate with each other to form supercomplexes (photosystems I and II), and with the electron transport components within and around the thylakoid membrane. Functionally, this results in the Z-scheme light-driven energy transduction system. Chlorophyll A: green; Chlorophyll B: orange; Carotene: red; Structural proteins: yellow

Photosynthesis Reaction center e- donor e- acceptor light

Photosynthesis The Cornerstone of Life on this planet! 6CO2+6H2O = C6H12O6 + 6O2 The Cornerstone of Life on this planet!

Vegetation Spectra In this graph = 1.0 [hemispherical reflectance] + [absorption] [hemispherical transmittance] = 1.0 [hemispherical reflectance] is displayed upwards from 0.0; [hemispherical transmittance] is displayed downward from 1.0; Rearranging the equation shows that [absorption] is the dark grey area between the two curves.  Conclusion: absorption dominates in visible; scattering dominates in the NIR.

Light absorption by leaf varies directly with leaf pigment concentrations Very high absorption Light absorption decreases as chlorophyll concentration decreases Very low absorption Very low chlorophyll concentration, very low light absorption Very high light absorption, very high chlorophyll concentration This figure is based upon hemispherical measurements for which, from conservation of energy, 1.0 = [hemispherical reflectance] + [absorption] + [hemispherical transmittance] Displaying hemispherical reflectance up from the bottom of the plot and hemispherical reflectance down from the top allows us to immediately visualize the light absorbed by the chlorophyll as the dark grey region in the middle, which at each wavelength has a magnitude given by [absorption] = 1.0 – [hemispherical reflectance] – [hemispherical transmittance]

Absorption is dominant process in visible; Scattering is dominant process in near infrared; Water absorption is increasingly important with increasing wavelength in the infrared.

Pigment Absorption Absorption Spectra of Chlorophyll a and b Absorption Efficiency 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 a. v iolet b lue g reen y ellow red Wavelength, m m Pigment Absorption Phycocyanin Phycoerythrin b -carotene Absorption Efficiency 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 v iolet b lue g reen y ellow red b. Wavelength, m m

Cell Wall Constituents

Protein Constituents

Cellular Water

Leaf Biochemistry Leaf biochemistry pigments: chlorophyll a and b, a-carotene, and xanthophyll absorb in blue (& red for chlorophyll) Absorbed radiation converted into: heat energy, fluorescence, or carbohydrates through photosynthesis Stored carbon!

Three factors determine canopy reflectance 2. Canopy architecture. (above-ground biomass; leaf area index; arrangement of foliage in x,y,z,q,f space – for example, are all leaves vertical and located in one layer – or perhaps they are arranged in space like the area on a sphere; etc.)

Chlorophyll and Carbon Assimilation “The big picture” Potential carbon assimilation by canopy Amount of chlorophyll in canopy (Concentration x phytomass)

Chlorophyll Concentrations Red or blue wavelength radiance, reflectance chlorophyll concentration

Chlorophyll and Carbon Assimilation “The big picture” Monteith Equation: The sum at each point in time of the product of Apar, the photosynthetically active radiation absorbed by the canopy, multiplied by the conversion efficiency of photons to assimilated carbon Actual carbon assimilated by canopy each day = Satellite remote sensing can provide estimates for one time during the day of Aparand/or Fpar, the fraction of the PAR intercepted by the canopy.

Hemispherical Hemispherical