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...ed by atmospheric watersvapor (1350–1480, 1780–2032 nm). Water vapor features preclude the use of these wavelength regionssin canopy chemical analyses.s2.6. Chemometric AnalysessWe used PLSR analysis =-=[26]-=- to characterize the strength of NSC expression in the spectroscopy ofsleaves, modeled canopies and actual canopies at the stand level. Leaf reflectance and transmittanceswere each tested using the fi...

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...ttance, and canopy reflectance, in the 400–2500 nm wavelength range.sSpectroscopy has an established history in the detection and analysis of leaf and canopy chemicalsRemote Sens. 2015, 7 3528straits =-=[12,13]-=-, but its use for NSC estimation is unproven. From both a theoretical and a laboratorysspectroscopy standpoint, remote sensing of foliar NSC should be possible based on the specificswavelength sensiti...

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...can besused as a general diagnostic for plant NSC, at least in a spatial or geographic context. Given thesobserved and predicted increases in drought frequency and severity in tropical forest regions =-=[7,8]-=-,sthere is a need for studies to determine foliar and whole-plant NSC concentrations as potentiallyspowerful predictors of drought tolerance [9]. This is particularly true in tropical forests, where l...

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...angle, both of whichsdo not vary as widely as tested here at spatial resolutions typical of airborne spectroscopy (>1 m).sHere, we selected extreme ranges compiled from the literature by Asner et al. =-=[23]-=- and Asner andsMartin [17] as a means to create possible worst-case scenarios of canopy structure overpowering leafsspectral-chemical variation. Our modeling also included a treatment of both random a...

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...can besused as a general diagnostic for plant NSC, at least in a spatial or geographic context. Given thesobserved and predicted increases in drought frequency and severity in tropical forest regions =-=[7,8]-=-,sthere is a need for studies to determine foliar and whole-plant NSC concentrations as potentiallyspowerful predictors of drought tolerance [9]. This is particularly true in tropical forests, where l...

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...ingsspectroscopy; soluble carbon; tropical forests1. IntroductionsNon-structural carbohydrates (NSC) are the mobile portion of a plant’s carbon stock, comprisedsprimarily of sugars, starch and pectin =-=[1,2]-=-. Also known as non-structural carbon or soluble carbon,splant NSC are produced and stored in leaves and can be transported to and stored in stems and roots.sPlant NSC stocks reflect a balance between...

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...ngsWe projected the mean leaf reflectance and transmittance spectra (n = 6136 pairs) to the canopyslevel using the 4SAIL2 (4-Stream Scattering by Arbitrarily Inclined Leaves) radiative transfersmodel =-=[20]-=-. This model simulates top-of-canopy spectral reflectance based on the measured leafshemispherical-directional reflectance and transmittance spectra, along with the variation of leaf areasindex (LAI),...

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...pressed in these spectra meets or exceedssthe variation reported for leaf optical properties in other biomes [29–34] and matches the reportedsvariability achieved in models of leaf optical properties =-=[19,35]-=-. This suggests that our leaf opticalsdatabase is globally relevant.sFigure 4. Leaf-level (a) reflectance and (b) transmittance spectra of fresh (live) samplesscollected from 6136 forest canopy growth...

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...anopy reflectance (n = 6136 simulated canopies) wasstested in a similar configuration, but with the 1330–1430-nm and 1760–2030-nm atmospheric watersvapor regions removed from the simulated VSWIR data =-=[27]-=-. Actual forest stand data (n = 79 fieldsplots) from the Amazon were treated the same way.sFor all PLSR analyses, we minimized statistical overfitting by utilizing the prediction residual errorssum of...

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... compounds, such as cellulose and lignin. As such, NSC measurements providesbiochemically-based insight into physiological performance (carbon “source”) relative to whole plantsgrowth (carbon “sink”) =-=[3,4]-=-.sNSC are important in trees and other perennial plants, because they provide chemical energy at timessof reduced resource availability, such as during dry periods or leaf-off periods in deciduous pla...

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...laboratorysspectroscopy standpoint, remote sensing of foliar NSC should be possible based on the specificswavelength sensitivities of sugars, starch and pectin in the shortwave region of the spectrum =-=[14,15]-=-.sSpectral features centered at 1450, 1490, 1510–1580, 1780, 1900, 1960, 2080–2100, and 2270–2280 nmsare particularly promising [14], but none or few wavelengths are likely to provide the informations...

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...pressed in these spectra meets or exceedssthe variation reported for leaf optical properties in other biomes [29–34] and matches the reportedsvariability achieved in models of leaf optical properties =-=[19,35]-=-. This suggests that our leaf opticalsdatabase is globally relevant.sFigure 4. Leaf-level (a) reflectance and (b) transmittance spectra of fresh (live) samplesscollected from 6136 forest canopy growth...

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...ize signal-to-noise performance; Analytical SpectrasDevices, Inc., Boulder, CO USA), an integrating sphere designed for high-resolution spectroscopicsmeasurements and a custom illumination collimator =-=[17]-=-. Twenty-five spectra per sample weresaveraged and then referenced to a calibration block within the integrating sphere (Spectralon,sLabsphere Inc., Durham, NH). An integrating sphere and collimated l...

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...ingsspectroscopy; soluble carbon; tropical forests1. IntroductionsNon-structural carbohydrates (NSC) are the mobile portion of a plant’s carbon stock, comprisedsprimarily of sugars, starch and pectin =-=[1,2]-=-. Also known as non-structural carbon or soluble carbon,splant NSC are produced and stored in leaves and can be transported to and stored in stems and roots.sPlant NSC stocks reflect a balance between...

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...ctra that did notsrequire smoothing or other filters commonly used in leaf optical studies.s2.3. Leaf NSC AssayssThe method for the chemical determination of leaf NSC was reported by Asner and Martin =-=[21]-=-, andsthe protocol is provided on the Spectranomics website (http://spectranomics.ciw.edu). Briefly, NSCsconcentration was determined in 0.5 g dry ground leaf tissue through using a neutral detergent ...

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...count spectral variation relative toschanging chemical concentration. In Figure 5, departures from zero indicate the increasing importancesof spectral features in determining a chemical concentration =-=[36]-=-. The most important features alignswith known centers of NSC expression in the spectrum, particularly from 1450 to 2270 nm, as detailedsby Curran [14].sTable 3. Calibration performances for non-struc...

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...laboratorysspectroscopy standpoint, remote sensing of foliar NSC should be possible based on the specificswavelength sensitivities of sugars, starch and pectin in the shortwave region of the spectrum =-=[14,15]-=-.sSpectral features centered at 1450, 1490, 1510–1580, 1780, 1900, 1960, 2080–2100, and 2270–2280 nmsare particularly promising [14], but none or few wavelengths are likely to provide the informations...

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...reme canopy structural variability compared to thesleaf-level analyses. This is important because, although past studies highlight the potential use ofsspectroscopy for canopy chemical trait analysis =-=[13,14,39]-=-, other studies have emphasized thespotentially dominant role of canopy structure over chemistry in determining canopy spectralsreflectance [40]. Here, we found insufficient evidence to suggest that s...

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...t is also far more variablesthan what is typically encountered in closed-canopy tropical forests [38]. Our leaf angle distributionssand other model parameters were also structurally very wide ranging =-=[18,20]-=-. Surprisingly, we foundsthat leaf NSC estimates from modeled canopy spectroscopy remained demonstrably good, althoughsprecision and accuracy did suffer under such extreme canopy structural variabilit...

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...re field plots distributedsRemote Sens. 2015, 7 3532sthroughout the Peruvian Amazon using the Carnegie Airborne Observatory (CAO) (Figure 3), whichsincludes a high-fidelity VSWIR imaging spectrometer =-=[24]-=-. In each field plot, multiple full-sunlightscanopies were selected for leaf collections (n = 3–38 per plot) as described in detail by Asner et al. [11].sFoliage from these canopies was assayed for NS...

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... LAI from 1.0 to 8.0 unitss(Table 2), which not only incorporates a global range of LAI values [23], but is also far more variablesthan what is typically encountered in closed-canopy tropical forests =-=[38]-=-. Our leaf angle distributionssand other model parameters were also structurally very wide ranging [18,20]. Surprisingly, we foundsthat leaf NSC estimates from modeled canopy spectroscopy remained dem...

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...fsspectroscopy for canopy chemical trait analysis [13,14,39], other studies have emphasized thespotentially dominant role of canopy structure over chemistry in determining canopy spectralsreflectance =-=[40]-=-. Here, we found insufficient evidence to suggest that structural variability in forestscanopies will critically impair NSC estimation from imaging spectroscopy.sAn additional finding was that the por...

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...l America, the Hawaiian Islands and Madagascar (Figure 2, Table 1). Thesglobal distribution of the samples, and their breakdown into plant families, genera and species, weresdescribed in Asner et al. =-=[16]-=-. Briefly, the dataset is comprised of the most common plant habits foundsin tropical forest canopies, including tree (n = 5233), liana (648), palm (74), hemi-epiphyte (109) andsvine (51). Across all ...

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...endale, CA USA). The reflectance imageryswas corrected for cross-track brightness gradients using a bidirectional reflectance distribution functions(BRDF) modeling approach described by Colgan et al. =-=[25]-=-. The sunlit portions of canopies in eachs1-ha plot were filtered and averaged based on the method described by Asner et al. (2015). Thissmethod removes pixels unsuitable for sunlit canopy spectroscop...

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...rea index; LAD = leaf angle distribution;sCv = crown covering the ground at nadir; Zeta = ratio of crown diameter to tree height. Thesmodeled LAI variation is considered extreme for tropical canopies =-=[22]-=-.sPlant Growth-form LAI LAD 1 Cv ZetasTrees 2.0–8.0s−0.4 to 0.4s−0.1 to 0.2 0.6–0.8 0.2–0.7sLianas 1.0–5.0s−0.1 to 0.3s0.3 to 0.6s0.7–0.9 0.1–0.3sPalms 1.0–5.0 −0.8 to −0.2 0.7–0.9 0.1–0.3sVines 1.0–3...

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...messof reduced resource availability, such as during dry periods or leaf-off periods in deciduous plants [5].sRecent work reveals that NSC are an important determinant of tree survival during drought =-=[6]-=-. In thatsstudy, tropical tree species with inherently low NSC stocks in foliage, stems, and roots were aboutstwice as likely to die in drought compared to those with naturally high NSC stocks. O’Brie...

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... compounds, such as cellulose and lignin. As such, NSC measurements providesbiochemically-based insight into physiological performance (carbon “source”) relative to whole plantsgrowth (carbon “sink”) =-=[3,4]-=-.sNSC are important in trees and other perennial plants, because they provide chemical energy at timessof reduced resource availability, such as during dry periods or leaf-off periods in deciduous pla...

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...(n = 79 fieldsplots) from the Amazon were treated the same way.sFor all PLSR analyses, we minimized statistical overfitting by utilizing the prediction residual errorssum of squares (PRESS) statistic =-=[28]-=-. The PRESS statistic was calculated through a cross-validationsprediction for each PLSR model. This cross-validation procedure iteratively generates regressionsmodels while reserving a portion of the...

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...with demonstrably high precisionsand accuracy compared to laboratory-based chemical assays. Laboratory wet-chemical assays of NSCstypically result in relative errors of about 9% on a per sample basis =-=[37]-=-, and our lab samplingsprotocols result in a similar error level. Leaf-level spectroscopy yielded relative errors ranging fromsjust 13%–14% (Table 3). When averaging samples and spectral signatures at...

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...ght frequency and severity in tropical forest regions [7,8],sthere is a need for studies to determine foliar and whole-plant NSC concentrations as potentiallyspowerful predictors of drought tolerance =-=[9]-=-. This is particularly true in tropical forests, where leafsNSC concentrations display strong phylogenetic and regional variation [10].sThe foliage of forest canopies is notoriously difficult to measu...

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...entrations as potentiallyspowerful predictors of drought tolerance [9]. This is particularly true in tropical forests, where leafsNSC concentrations display strong phylogenetic and regional variation =-=[10]-=-.sThe foliage of forest canopies is notoriously difficult to measure at any scale. Tall canopies andscomplex architectures preclude access and limit field collections to a few leaves or branches persc...

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...s perscrown. The data resulting from such approaches are challenging to interpret or to scale up and are notsoften random or systematic samples of an individual tree, a canopy of trees or a landscape =-=[11]-=-.sRemote measurement of foliar traits is the only way to accurately sample at stand and ecosystemslevels, but remote sensing approaches for NSC estimation have not been broadly developed. Twosscales o...

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...s consistency in thesexpression of foliar NSC in leaf and canopy reflectance spectra.sThe total carbon content of a leaf is approximately equal to the sum of NSC, cellulose,shemi-cellulose and lignin =-=[41]-=-. One might therefore predict that remote sensing of NSC is somehowsinversely related to remote estimation of the other carbon molecules, and indeed, lignin and celluloseshave long been a focus of ima...